Why is electricity so hard to understand? (1989)(amasci.com)
amasci.com
Why is electricity so hard to understand? (1989)
http://amasci.com/miscon/whyhard2.html
148 comments
Funny that you say frame of reference, since electricity does change when we change our frame of reference. For example, a moving charge generates a magnetic field, but if we move along with that charge it becomes a non-moving charge and suddenly it generates an electrostatic field instead.
Can someone explain wattage and voltage, how are they applicable, why are they useful and which one can hurt me?
I have watched many YouTube videos. I understand that electricity is electrons moving through a conductor from “+” to “-“ but am at a loss of why they move and why do we have two measurements for one thing.
I have watched many YouTube videos. I understand that electricity is electrons moving through a conductor from “+” to “-“ but am at a loss of why they move and why do we have two measurements for one thing.
Power (watts) and voltage (volts) are not the same thing.
The water analogy is most useful at this level (despite being wrong in most respects, it instils a basic working understanding good enough for the householder).
Think of a waterfall. Wait, think of two: a very high one with just a thin stream of water, and a low one, maybe a foot high with a torrent of water flowing over it (a weir).
Voltage is the height of the waterfall: a stream of water at the bottom of a very high waterfall will feel more painful than a stream from a much lower one.*
Current is analogous to the amount of water flowing over the waterfall - the river's current.
Multiplying voltage by current, you get power: the ability of the waterfall to do useful work.
(A very high waterfall with hardly any water flowing over it won't be able to turn a water wheel very quickly, and nor will a very low waterfall with a lot of water flowing over it. You need both voltage and current to do useful work.)
Re the movement of electrons: in fact they move very slowly on average under the influence of an electric field, but by their "bouncing against" their neighbours, the electric impulse is transmitted quickly through the conductor.
* An alternative analogue for voltage is water pressure, and indeed in some languages voltage is referred to as pressure.
The water analogy is most useful at this level (despite being wrong in most respects, it instils a basic working understanding good enough for the householder).
Think of a waterfall. Wait, think of two: a very high one with just a thin stream of water, and a low one, maybe a foot high with a torrent of water flowing over it (a weir).
Voltage is the height of the waterfall: a stream of water at the bottom of a very high waterfall will feel more painful than a stream from a much lower one.*
Current is analogous to the amount of water flowing over the waterfall - the river's current.
Multiplying voltage by current, you get power: the ability of the waterfall to do useful work.
(A very high waterfall with hardly any water flowing over it won't be able to turn a water wheel very quickly, and nor will a very low waterfall with a lot of water flowing over it. You need both voltage and current to do useful work.)
Re the movement of electrons: in fact they move very slowly on average under the influence of an electric field, but by their "bouncing against" their neighbours, the electric impulse is transmitted quickly through the conductor.
* An alternative analogue for voltage is water pressure, and indeed in some languages voltage is referred to as pressure.
In Turkish voltage is known both as voltaj and gerilim. Gerilim means tension, coming from the verb germek, which means to stretch. I think tension is a good analogy, and fits with the idea of potential and springs.
Tension is used in English to mean voltage sometimes too!
The most common place I can think of is in the HT (High Tension) leads leading to a car's spark plugs: https://en.wikipedia.org/wiki/High_tension_leads
The most common place I can think of is in the HT (High Tension) leads leading to a car's spark plugs: https://en.wikipedia.org/wiki/High_tension_leads
THAT is what high tension wires are?! I've always seen it in the context of the massive transmission lines, so I thought it meant that the wires themselves were under high tension from their weight.
Also "high tension power lines," which being heavy catenaries presumably are in high mechanical tension, but must surely have gotten that name from the voltage = tension thing.
German has this too: voltage = Spannung = tension.
This must go right back to the earliest writings on voltage as a concept.
German has this too: voltage = Spannung = tension.
This must go right back to the earliest writings on voltage as a concept.
French also has "tension" in this very sense.
https://fr.wikipedia.org/wiki/Tension_%C3%A9lectrique
https://fr.wikipedia.org/wiki/Tension_%C3%A9lectrique
In spanish "Voltage" (i.e. voltaje) is "tensión" (tension) or "diferencia de potencial" (potential difference).
A problem here is that "tension" communicates a concept, but "voltage" communicates nothing, it's only a derivation of the unit used, or perhaps something to do with Alessandro Volta, a gentleman most students these days hadn't the pleasure to meet.
A simmilar problem in spanish was "amperaje" (amperage) which is not much heard any more except very colloquially among electricians; the standard term is "corriente" (current).
However, the units and letters are somewhat confusing for the students:
V(oltage) = E(lectric field?), unit is Volt, is refered as tension of potential differece. A(mp) = I(ntensity), unit is Ampere, is refered as corriente. P(ower), unit Watt, is consistent, as is refered as potencia (power).
A simmilar problem in spanish was "amperaje" (amperage) which is not much heard any more except very colloquially among electricians; the standard term is "corriente" (current).
However, the units and letters are somewhat confusing for the students:
V(oltage) = E(lectric field?), unit is Volt, is refered as tension of potential differece. A(mp) = I(ntensity), unit is Ampere, is refered as corriente. P(ower), unit Watt, is consistent, as is refered as potencia (power).
In Russian it is напряжение. Which can be loosely translated as tension, but more in the sense of a feeling than of a characteristic of a rope or a spring (that's натяжение).
In some languages voltage is called "pressure". I think this is also a good analogy because just like how you get energy from a pneumatic system by exploiting a pressure difference, you get energy from an electrical system by exploiting a potential difference
That analogy would work. In that case voltage (volts) would be the tension on a rubber band, current (amps) would be the width of the rubber band, ad Power (watts) would be the product of tension times the diameter (or mass).
> they move very slowly on average
Each electron moves slowly, but they all move approximately in the same direction st the same time, so the net effect is to move charge berry quickly, right?
Like a bucket brigade where everyone passes water to the person on their left. You move a bucket 3 feet per second, but together everyone moves a bucket worth of water a hundred feet per second.
Each electron moves slowly, but they all move approximately in the same direction st the same time, so the net effect is to move charge berry quickly, right?
Like a bucket brigade where everyone passes water to the person on their left. You move a bucket 3 feet per second, but together everyone moves a bucket worth of water a hundred feet per second.
No, this is the whole "confusing the wave and the medium" problem. Drift velocity (the technical name for "how fast are electrons moving through this wire") has effectively nothing at all to do with the propagation of electrical properties through a circuit.
If electrical properties propagated at the drift velocity, there'd be an appreciable delay when you flipped your light switch.
If electrical properties propagated at the drift velocity, there'd be an appreciable delay when you flipped your light switch.
> Re the movement of electrons: in fact they move very slowly on average under the influence of an electric field, but by their "bouncing against" their neighbours, the electric impulse is transmitted quickly through the conductor.
When you apply a voltage across a conductor it generates an electric field, and the electric field propagates at the speed of light (it’s an EM wave). I could be wrong, but I think that is why the electric impulse transmits quickly even though the drift velocity is so slow.
When you apply a voltage across a conductor it generates an electric field, and the electric field propagates at the speed of light (it’s an EM wave). I could be wrong, but I think that is why the electric impulse transmits quickly even though the drift velocity is so slow.
Electrons move because you have an electric field. Like charges repel while opposites attract, so if you have a excess of protons at one point, an excess of electrons at another point, and a wire connecting the two points, then the electromotive force will push the electrons through the wire to try to balance out the charges (see Coulomb’s law [0]).
In the process, the electrons gain kinetic energy, and if you’re clever you can extract this energy to do useful work. Voltage [1] is defined as joules per coulumb, where joules is a measurement of energy, and coulomb is a measurement of electric charge — one coulomb is the charge carried by 6x10^18 electrons. A voltage is always between two points, so if the voltage difference between point A and point B is 1V, then moving 6e18 electrons from point A to point B will produce 1J of energy; or, conversely, it would require 1J of energy to move the electrons back “uphill” in the opposite direction. (Actually, that’s sort of backwards because electrons carry a negative charge and so flow from the negative side of a battery to the positive, but that’s not terribly important right now.)
Current [2] is the rate at which electrons are flowing, defined simply as coulombs per second. You can calculate the rate of energy flow by multiplying voltage (energy per unit charge) by current (charge per second) to get watts [3], which is defined as joules per second.
If you want to learn more, there’s lots of excellent resources online — but if you really want a solid understanding from first principles, you might be better off taking an introductory physics course at a community college.
[0]: https://en.m.wikipedia.org/wiki/Coulomb%27s_law
[1]: https://en.m.wikipedia.org/wiki/Voltage
[2]: https://en.m.wikipedia.org/wiki/Electric_current
[3]: https://en.m.wikipedia.org/wiki/Electric_power
In the process, the electrons gain kinetic energy, and if you’re clever you can extract this energy to do useful work. Voltage [1] is defined as joules per coulumb, where joules is a measurement of energy, and coulomb is a measurement of electric charge — one coulomb is the charge carried by 6x10^18 electrons. A voltage is always between two points, so if the voltage difference between point A and point B is 1V, then moving 6e18 electrons from point A to point B will produce 1J of energy; or, conversely, it would require 1J of energy to move the electrons back “uphill” in the opposite direction. (Actually, that’s sort of backwards because electrons carry a negative charge and so flow from the negative side of a battery to the positive, but that’s not terribly important right now.)
Current [2] is the rate at which electrons are flowing, defined simply as coulombs per second. You can calculate the rate of energy flow by multiplying voltage (energy per unit charge) by current (charge per second) to get watts [3], which is defined as joules per second.
If you want to learn more, there’s lots of excellent resources online — but if you really want a solid understanding from first principles, you might be better off taking an introductory physics course at a community college.
[0]: https://en.m.wikipedia.org/wiki/Coulomb%27s_law
[1]: https://en.m.wikipedia.org/wiki/Voltage
[2]: https://en.m.wikipedia.org/wiki/Electric_current
[3]: https://en.m.wikipedia.org/wiki/Electric_power
Another good word for voltage is potential.
In a battery, the energy moves through the external circuit because the internals of the battery have been arranged so that an energy releasing chemical reaction is completed when that happens.
In an alternator, a conductor is moved through a magnetic field, which induces a current (this arises out of the properties of magnetic fields; https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction ).
Voltage and power are related by current. Power = voltage x current.
The amount of current that flows through a circuit depends on the voltage potential and the properties of the circuit. Our bodies aren't particularly good circuits, so lower voltages won't push much current through a circuit that includes it. A car battery isn't a big electrocution risk, it is dangerous because it can release a lot of energy quickly (it has fairly high power). Somewhere around 50 volts, current does start to flow through our bodies, causing problems even at relatively low currents (and thus low power), heart disruption and such.
In a battery, the energy moves through the external circuit because the internals of the battery have been arranged so that an energy releasing chemical reaction is completed when that happens.
In an alternator, a conductor is moved through a magnetic field, which induces a current (this arises out of the properties of magnetic fields; https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction ).
Voltage and power are related by current. Power = voltage x current.
The amount of current that flows through a circuit depends on the voltage potential and the properties of the circuit. Our bodies aren't particularly good circuits, so lower voltages won't push much current through a circuit that includes it. A car battery isn't a big electrocution risk, it is dangerous because it can release a lot of energy quickly (it has fairly high power). Somewhere around 50 volts, current does start to flow through our bodies, causing problems even at relatively low currents (and thus low power), heart disruption and such.
Wattage is simply voltage x amperage. It's the law. Watt's Law.
Watts are a measure of energy, just different units than calories or BTU.
Voltage is a measure of difference in _potential_, and amperage is a measure of current being moved. So electrical energy depends on a bit of both.
Beyond a certain voltage, it can be somewhat shocking. High enough and it can jump out at you.
And it can be badly damaging.
Also depends on how conductive you are at the time, conductance is the opposite of resistance.
Also depends on how much amperage is available from the source, if the source is fused for 1 amp maximum it would be less risky than higher amperage fuses.
Like with household wiring, if you get shocked and are conductive enough for significant amperage to be passed through your body, the total wattage could be enough of a fraction of a space heater's dissipation to roast the tissues which are involved with conducting the current.
Simply because there's enough amperage available at that voltage to get a space heater red hot, and the circuit breaker will not trip unless you are conducting more than that.
OTOH, sensitive organs can be upset by much lower amperage if it passes along lines where the organs are nearby.
For instance if you work on an electrical box and take a shock from your right hand to your right elbow, it's mainly going to hurt that one arm.
But contact the same two points, one to each elbow, and the heart is at risk much more than before, since the current has to pass through your torso to complete the circuit.
Watts are a measure of energy, just different units than calories or BTU.
Voltage is a measure of difference in _potential_, and amperage is a measure of current being moved. So electrical energy depends on a bit of both.
Beyond a certain voltage, it can be somewhat shocking. High enough and it can jump out at you.
And it can be badly damaging.
Also depends on how conductive you are at the time, conductance is the opposite of resistance.
Also depends on how much amperage is available from the source, if the source is fused for 1 amp maximum it would be less risky than higher amperage fuses.
Like with household wiring, if you get shocked and are conductive enough for significant amperage to be passed through your body, the total wattage could be enough of a fraction of a space heater's dissipation to roast the tissues which are involved with conducting the current.
Simply because there's enough amperage available at that voltage to get a space heater red hot, and the circuit breaker will not trip unless you are conducting more than that.
OTOH, sensitive organs can be upset by much lower amperage if it passes along lines where the organs are nearby.
For instance if you work on an electrical box and take a shock from your right hand to your right elbow, it's mainly going to hurt that one arm.
But contact the same two points, one to each elbow, and the heart is at risk much more than before, since the current has to pass through your torso to complete the circuit.
> Watts are a measure of energy, just different units than calories or BTU.
Sorry to be pedantic, but watts are a unit of power, not energy. Power is energy divided by time. The unit of energy is a joule (or, more commonly in household terms, a Watt-hour).
Sorry to be pedantic, but watts are a unit of power, not energy. Power is energy divided by time. The unit of energy is a joule (or, more commonly in household terms, a Watt-hour).
Thanks for that, I wasn't being completely accurate with my terminology.
Wait, is that right? I thought that was one of those "lies to children". I mean, yes, the electrons move (er...drift), but I thought the important thing is that it's the charge that moves, not the electrons.
At least it's not just me that thinks the usual explanations are lacking.
At least it's not just me that thinks the usual explanations are lacking.
[deleted]
Right. This passage from TFA hits on that:
> ...mistaking the wave for the medium. Is "electricity" the electrons, or is it the wave of electron-flow, or is it energy that flows THROUGH a column of electrons. Think of how difficult it would be to understand sound waves and air pressure if we had just a single word that meant both "sound" and "wind" and "air."
> ...mistaking the wave for the medium. Is "electricity" the electrons, or is it the wave of electron-flow, or is it energy that flows THROUGH a column of electrons. Think of how difficult it would be to understand sound waves and air pressure if we had just a single word that meant both "sound" and "wind" and "air."
Sound : AC (maybe? Not sure.)
Wind : DC
Air : conductor
Wind : DC
Air : conductor
I think in this analogy, sound is more like voltage in the sense that voltage is like pressure: it’s a measure of potential per electron or force per air molecule. And when you push on the electrons at one end of a wire, that pressure change rapidly propagates to the other end of the wire even without the electrons moving. Like the way sound doesn’t involve air molecules flowing from place to place but is a pressure wave.
Wind is like electrical current in the sense that you set up a pressure difference between one point and another, and then you open up a little path for the electrons/air molecules to flow through, then they will move along that path, and the amount of air molecules/electrons flowing past a point per second is the current/wind. That’s the analogy.
Wind is like electrical current in the sense that you set up a pressure difference between one point and another, and then you open up a little path for the electrons/air molecules to flow through, then they will move along that path, and the amount of air molecules/electrons flowing past a point per second is the current/wind. That’s the analogy.
The charge and the electrons are the same thing (at least in a normal conductor). Both move very slowly. But energy moves through them very quickly (fluid analogy is helpful here: when you pump water into a full hose then water starts flowing out of the hose quickly even though it may take a long time for the water you just pumped in to exit. In electricity the difference is even more extreme).
Correct. In a related concept, I had a professor that explained it as a combination of electron flow in one direction, and "hole" [1] flow in the other. Either way of looking at it is valid.
[1] https://en.m.wikipedia.org/wiki/Electron_hole
edit: I'm not sure, on second thought, how far you can really go with that. Lightning clearly has directionality to it.
[1] https://en.m.wikipedia.org/wiki/Electron_hole
edit: I'm not sure, on second thought, how far you can really go with that. Lightning clearly has directionality to it.
But lightning is where the gas has broken down, turning into plasma. Lightning is a growing conductor, like a motorized antenna on an oldschool car radio.
The growth of lightning is much like a growing metal dendrite-crystal.
Also, when lightning leaps rapidly upwards, the electrons INSIDE the lightning are flowing slowly downwards. The extending tip of a lightning-streamer is not an electric current, it's more like the moving tip of a growing fracture.
The growth of lightning is much like a growing metal dendrite-crystal.
Also, when lightning leaps rapidly upwards, the electrons INSIDE the lightning are flowing slowly downwards. The extending tip of a lightning-streamer is not an electric current, it's more like the moving tip of a growing fracture.
Some of the physics videos by this guy may be helpful:
https://www.youtube.com/channel/UCJ0yBou72Lz9fqeMXh9mkog
https://www.youtube.com/channel/UCJ0yBou72Lz9fqeMXh9mkog
First, set aside wattage for a moment, it's a derived unit.
The key units are amps (current) and volts (voltage aka potential difference). In the commonly used water analogy voltage is water pressure, and current is amount of water that flows through per unit of time.
It's the current that kills you. But voltage and current are related, in many cases by Ohm's law: current is proportional to voltage, with coefficient called conductance (the inverse of which is resistance). That's why high voltage is more dangerous.
The key units are amps (current) and volts (voltage aka potential difference). In the commonly used water analogy voltage is water pressure, and current is amount of water that flows through per unit of time.
It's the current that kills you. But voltage and current are related, in many cases by Ohm's law: current is proportional to voltage, with coefficient called conductance (the inverse of which is resistance). That's why high voltage is more dangerous.
Even a question like this isn't so simple. There's at least a couple of ways electricity can hurt you. One is by interrupting the regular body regulation mechanisms, namely your heartbeat. Electricity passing across the heart can cause it to spasm. If it can't recover and find a regular heartbeat again you die. This is the most common way to get hurt and could happen from getting a shock from mains. The other is by electricity passing through you and burning you on the way through. This is common from lightning strikes as the electricity will pass through you to ground, rather than across the heart. It means you're less likely to die, but more likely to sustain injury.
In all cases, what hurts you is current. Current means electrons are flowing through you. As mentioned there are at least a couple of ways that current can affect you adversely. So it needs to be either a large enough current (so more electrons flowing), or a current going in the wrong place (across the heart).
So what makes current flow? Or, why do the electrons "want" to move? Voltage. A car battery has plenty of energy in it that could kill you in either of the two ways, but at 12V there's not enough voltage to get any current flowing through your body.
Voltage is the existence of an imbalance. Electrons "want" to be in a place where they are balanced with a positive charge. A battery represents a structure that is very imbalanced but the electrons are not able to move anywhere until the two ends of the battery are connected with a conductor. There are many ways that these imbalances arise but they are ultimately always the result of energy going in. When the imbalance is resolved the energy comes back out.
To hurt you a voltage also needs to be sustained long enough to pass enough current. A static shock is due to a very high voltage existing which it causes current to flow and why you can feel it, unlike the car battery. However, in an instant all the current has flowed and the voltage is gone.
So the answer is a high enough voltage and enough energy to sustain that voltage. Mains electricity can hurt you because it's high voltage (>50V) and can sustain that voltage all day long. Lightning can hurt you because it's very high voltage and can sustain it long enough (and that's only an instant) to cause serious injury.
In all cases, what hurts you is current. Current means electrons are flowing through you. As mentioned there are at least a couple of ways that current can affect you adversely. So it needs to be either a large enough current (so more electrons flowing), or a current going in the wrong place (across the heart).
So what makes current flow? Or, why do the electrons "want" to move? Voltage. A car battery has plenty of energy in it that could kill you in either of the two ways, but at 12V there's not enough voltage to get any current flowing through your body.
Voltage is the existence of an imbalance. Electrons "want" to be in a place where they are balanced with a positive charge. A battery represents a structure that is very imbalanced but the electrons are not able to move anywhere until the two ends of the battery are connected with a conductor. There are many ways that these imbalances arise but they are ultimately always the result of energy going in. When the imbalance is resolved the energy comes back out.
To hurt you a voltage also needs to be sustained long enough to pass enough current. A static shock is due to a very high voltage existing which it causes current to flow and why you can feel it, unlike the car battery. However, in an instant all the current has flowed and the voltage is gone.
So the answer is a high enough voltage and enough energy to sustain that voltage. Mains electricity can hurt you because it's high voltage (>50V) and can sustain that voltage all day long. Lightning can hurt you because it's very high voltage and can sustain it long enough (and that's only an instant) to cause serious injury.
A car battery can hurt you by generating a lot of resistive heat that burns your skin.
It won't kill you quickly, though.
It won't kill you quickly, though.
Just by holding the terminals with dry hands? No current will flow through you will it?
More like by grabbing something metal and using it to bridge across the two terminals. It will get very hot very quickly.
Wear your safety glasses and other PPE before vaporizing metal coathangers this way.
Right, so you can add that as a third way electricity can harm you.
Not nearly as much as in a marine environment with wet salty hands.
Not an expert here but there are not two measurements for one thing. You need to precisely understand basic physics mechanics concepts like force and work before any answers will make sense. BBC youtube series is a great intro.
> I understand that electricity is electrons moving through a conductor from “+” to “-“
Actually they move from "-" to "+" :)
Actually they move from "-" to "+" :)
Electrons are.. we don't really know what they are. What we do know is that they have a "charge" around them, an "electric potential", and that they repel each other.
"Electricity" is one of those terms that doesn't really have a specific meaning. From what i see, we use it to group all the electromagnetic things that.. i guess deal with "loose" electrons.
As for the actual question, first i'd have to explain "electric current". Current (in Amperes) is just the flow of electrons. As in how many electrons flow through some plane over time. In practical terms; how many electrons flow through a wire, where the "plane" is the diameter of wire.
Voltage is a force. Imagine that the electrons weren't points that repealed each other, but were instead balls. You fill up a pipe with balls and push on one side of it. The force you are pushing with is the "voltage". You can also imagine this with water, where the pressure is.. well it's all the same really when we get "low" enough. Note that electrons, unlike balls and water, don't really have mass.
Wattage is power. It is how much energy is.. transmitted over time. You pay your bills in Watt * Hours, but you might as well pay it in Joules. It shows you how much power you can expect from a machine. Wattage is calculated by multiplying Voltage and current, as in how hard you push and how many electrons you push per time. In water terms, it is the speed of the water multiplied by how big the river is (or pipe).
So they are useful units of measurement, just as any other metric unit of measurement. In fact Ampere is one of the seven basic units of measurement in the Systeme international d'unites (SI, often called "metric").
The one that actually hurts you is the current. The thing is that Voltage "pushes" the current, so one might rightfully think that "high" Voltage is the dangerus one. But again you can touch a 100000 Volt sphere on top of a Van de Graaff generator, because it doesn't have enough electrons in it to make a current "big" enough to kill you. The current across the heart, that is enough to stop your heart, is about 50mA (as far as i remember), and that is very little current. Your heart is in between your hands, so you would need to hold "+" in one hand and "-" in another for current to go through it. You can also die from poisoning if a large current burns your flesh, and other similar bad things. If you think there's a danger from electricity, use just one hand so that the current goes through your legs, missing the heart (also watch for the top of your head, because brain). If the voltage is really high, like a transmission line cable falls right beside you, put your feet together and hop away. Like 10 meters away should be fine, idk. To be clear, you can touch the leads on your 12 Volt car battery and nothing will happen to you, in spite of the car battery being easily capable of delivering a big(ish) current of a 100 Amperes (but if you connect the leads with a wire, it will melt and burn you).
For fun i measured my palm to palm resistance just now. It's ~2 mega Ohms currently. So saying i need 50 mili Amps through my heart to stop it, i'd need (V = 0.05 * 2000000) 100000 Volts minimum. But that is for "direct" current (DC, not AC), and it doesn't take a lot of other things in to account. In reality 220 Volts AC could be enough. On the other hand, i know many people survived grabbing the "hot" wire and ground with their other hand, and the only one i vaguely remember died has fallen of a ladder because of the shock.
So in short; Wattage is power, Voltage is.. force, they are used to calculate things involving a lot of stuff (and safety), and the current hurts you because Voltage told it to.
PS Feel free to ask if something is not clear, i misinterpreted your question, something else you want to know or expand upon, etc, etc
"Electricity" is one of those terms that doesn't really have a specific meaning. From what i see, we use it to group all the electromagnetic things that.. i guess deal with "loose" electrons.
As for the actual question, first i'd have to explain "electric current". Current (in Amperes) is just the flow of electrons. As in how many electrons flow through some plane over time. In practical terms; how many electrons flow through a wire, where the "plane" is the diameter of wire.
Voltage is a force. Imagine that the electrons weren't points that repealed each other, but were instead balls. You fill up a pipe with balls and push on one side of it. The force you are pushing with is the "voltage". You can also imagine this with water, where the pressure is.. well it's all the same really when we get "low" enough. Note that electrons, unlike balls and water, don't really have mass.
Wattage is power. It is how much energy is.. transmitted over time. You pay your bills in Watt * Hours, but you might as well pay it in Joules. It shows you how much power you can expect from a machine. Wattage is calculated by multiplying Voltage and current, as in how hard you push and how many electrons you push per time. In water terms, it is the speed of the water multiplied by how big the river is (or pipe).
So they are useful units of measurement, just as any other metric unit of measurement. In fact Ampere is one of the seven basic units of measurement in the Systeme international d'unites (SI, often called "metric").
The one that actually hurts you is the current. The thing is that Voltage "pushes" the current, so one might rightfully think that "high" Voltage is the dangerus one. But again you can touch a 100000 Volt sphere on top of a Van de Graaff generator, because it doesn't have enough electrons in it to make a current "big" enough to kill you. The current across the heart, that is enough to stop your heart, is about 50mA (as far as i remember), and that is very little current. Your heart is in between your hands, so you would need to hold "+" in one hand and "-" in another for current to go through it. You can also die from poisoning if a large current burns your flesh, and other similar bad things. If you think there's a danger from electricity, use just one hand so that the current goes through your legs, missing the heart (also watch for the top of your head, because brain). If the voltage is really high, like a transmission line cable falls right beside you, put your feet together and hop away. Like 10 meters away should be fine, idk. To be clear, you can touch the leads on your 12 Volt car battery and nothing will happen to you, in spite of the car battery being easily capable of delivering a big(ish) current of a 100 Amperes (but if you connect the leads with a wire, it will melt and burn you).
For fun i measured my palm to palm resistance just now. It's ~2 mega Ohms currently. So saying i need 50 mili Amps through my heart to stop it, i'd need (V = 0.05 * 2000000) 100000 Volts minimum. But that is for "direct" current (DC, not AC), and it doesn't take a lot of other things in to account. In reality 220 Volts AC could be enough. On the other hand, i know many people survived grabbing the "hot" wire and ground with their other hand, and the only one i vaguely remember died has fallen of a ladder because of the shock.
So in short; Wattage is power, Voltage is.. force, they are used to calculate things involving a lot of stuff (and safety), and the current hurts you because Voltage told it to.
PS Feel free to ask if something is not clear, i misinterpreted your question, something else you want to know or expand upon, etc, etc
Actually electrons are moving from - to +.
I'll try. Some have done a decent job here already.
Watts = volts * current (amps). It's hard to compare words like "force" and "quantity" for volts and amps, but here's maybe a practical definition.
High voltage is dangerous because it can leap through air (arc) to form a circuit. If part of that circuit is _you_ (like, from a high-voltage wire, through you, to the ground), then you can be made dead, quite quickly. That's why high-voltage (sometimes called "high-tension") wires are carried by tall towers with the wires far apart -- if the wires were closer together, they could arc between them and short out.
Essentially, high voltage overcomes insulation -- whether the insulation is air (for high-above-ground wires) or various forms of plastic (for wires buried underground). That's what makes it dangerous, and why electrical panels have warnings that say "Danger: High Voltage".
But even very high voltage won't hurt you if the current (amps) is too low. But "low current" isn't something you typically encounter in, for example, household AC wiring because the supply of current is generally very large.
So high voltage can kill you, but only if the current (amps) is high enough. In most practical situations where you might be exposed to electricity from the grid, the current is plenty high. That's why the signs say "Danger: High Voltage" and not "Danger: High Amps" or "Danger: High Power" (watts).
But how high is "high"?
A 12-volt car battery (I wonder how long that term will be meaningful...) isn't very high voltage. You can safely put your dry fingers across the terminals of a 12v battery and not feel a thing.
On the other hand, the 120-volt (or 240-volt) electricity coming out of a wall socket is most definitely unsafe to grab with your dry fingers. I've been accidentally shocked dozens of times by 120v electricity, and it is attention-getting. It can kill you fairly easily if, for example, the alternating current of the electricity causes your muscles to contract, forcing you to hold on ever more tightly to the wires. Usually, it's your heart in the path of the current that takes the, um, beating. If you get a shock across just the one hand that you're sticking accidentally into a live electrical box, your tendency is to retract your arm. Very quickly.
But even 120 or 240 volts won't jump across very much air, like, essentially, none.
Compare that to the 100,000+ volts that are carried by the high-tension lines at the top of int[er|ra]state transmission lines -- that's enough voltage to arc across many inches of air without any trouble at all.
So why do we use high voltage at all, why can't we just use low voltage everywhere and be safer?
That's where the magic of the power equation (Power (watts) = Volts * Amps) comes in. But that's for another discussion.
Watts = volts * current (amps). It's hard to compare words like "force" and "quantity" for volts and amps, but here's maybe a practical definition.
High voltage is dangerous because it can leap through air (arc) to form a circuit. If part of that circuit is _you_ (like, from a high-voltage wire, through you, to the ground), then you can be made dead, quite quickly. That's why high-voltage (sometimes called "high-tension") wires are carried by tall towers with the wires far apart -- if the wires were closer together, they could arc between them and short out.
Essentially, high voltage overcomes insulation -- whether the insulation is air (for high-above-ground wires) or various forms of plastic (for wires buried underground). That's what makes it dangerous, and why electrical panels have warnings that say "Danger: High Voltage".
But even very high voltage won't hurt you if the current (amps) is too low. But "low current" isn't something you typically encounter in, for example, household AC wiring because the supply of current is generally very large.
So high voltage can kill you, but only if the current (amps) is high enough. In most practical situations where you might be exposed to electricity from the grid, the current is plenty high. That's why the signs say "Danger: High Voltage" and not "Danger: High Amps" or "Danger: High Power" (watts).
But how high is "high"?
A 12-volt car battery (I wonder how long that term will be meaningful...) isn't very high voltage. You can safely put your dry fingers across the terminals of a 12v battery and not feel a thing.
On the other hand, the 120-volt (or 240-volt) electricity coming out of a wall socket is most definitely unsafe to grab with your dry fingers. I've been accidentally shocked dozens of times by 120v electricity, and it is attention-getting. It can kill you fairly easily if, for example, the alternating current of the electricity causes your muscles to contract, forcing you to hold on ever more tightly to the wires. Usually, it's your heart in the path of the current that takes the, um, beating. If you get a shock across just the one hand that you're sticking accidentally into a live electrical box, your tendency is to retract your arm. Very quickly.
But even 120 or 240 volts won't jump across very much air, like, essentially, none.
Compare that to the 100,000+ volts that are carried by the high-tension lines at the top of int[er|ra]state transmission lines -- that's enough voltage to arc across many inches of air without any trouble at all.
So why do we use high voltage at all, why can't we just use low voltage everywhere and be safer?
That's where the magic of the power equation (Power (watts) = Volts * Amps) comes in. But that's for another discussion.
There’s indeed something terribly wrong with the way they explain/teach electricity, to the point that I sometimes suspect that whoever is doing it are themselves confused, whether they realize it or not. In particular, I am yet to find a lucid and intuitive explanation of why we need both E and D for the electric field and B and H for the magnetic field. (And no, talking about them being “differential forms” of various kinds is not helpful in most cases.) Also, the multitude of systems of units does not help learning, either.
E = q2 F basically motivates & defines the electric field from first principles by normalizing the force against the charge of the particle experiencing it. It relates the object to the properties of its surrounding space.
D = q1 / 4 pi R^2 describes the effect the first particle has on space at the location of the second particle. It relates the subject to the properties of its surrounding space.
And D = E epsilon of course tells you how those quantities relate to each other. It's basically the verb. Together these describe how two stationary particles interact with each other electrically. They link the subject and object together. Think of it as subject -> verb -> object.
The motivation for all of is to decouple things so we can reason about them independently.
Hopefully that's lucid and intuitive?
D = q1 / 4 pi R^2 describes the effect the first particle has on space at the location of the second particle. It relates the subject to the properties of its surrounding space.
And D = E epsilon of course tells you how those quantities relate to each other. It's basically the verb. Together these describe how two stationary particles interact with each other electrically. They link the subject and object together. Think of it as subject -> verb -> object.
The motivation for all of is to decouple things so we can reason about them independently.
Hopefully that's lucid and intuitive?
You would think that (oh the curse of knowledge!), but there is still something that muddies the waters here. It is the missing relation between the physical electric field which is what the free charges actually generate and the (still mysterious) displacement field. This makes your explanation more abstract that it needs to be. The "D = E epsilon" that you mention in passing is in fact another source of confusion, because it is not clear whether E is what the free charges ("q1") generate or it is what acts on the probe ("q2").
> I am yet to find a lucid and intuitive explanation of why we need both E and D for the electric field and B and H for the magnetic field.
E alone cannot describe fully state of dielectric, and B alone cannot fully describe state of magnetic medium. We need additional concepts, either charge/current densities, or polarization/magnetization, or D/H, in that order of importance.
In modern understanding, D and H are auxiliary concepts that are useful mainly in special but important cases they were historically devised for. Let's take D for example. If free charge is absent, Maxwell's equations imply very nice equation div D = 0. The equation for E is more complicated (includes bound charge density that is hard to measure, hard to relate to other things in the model and so is usually preferred to be ignored).
If in addition the medium is linear (a special but important case), D is a simple linear function of E ( there is no such simple relation to charge density or current density) so things such as the concept of EM energy in medium is possible, and wave propagation in crystals can be analyzed most elegantly. Sure, all could be analyzed in terms of E and rho and j which would be more "physical" but it is not the most elegant way to do it. It is like in mechanics: we can analyze complicated systems with constraints by writing down many equations involving constraint forces, but there are easier methods such as the Lagrangian.
E alone cannot describe fully state of dielectric, and B alone cannot fully describe state of magnetic medium. We need additional concepts, either charge/current densities, or polarization/magnetization, or D/H, in that order of importance.
In modern understanding, D and H are auxiliary concepts that are useful mainly in special but important cases they were historically devised for. Let's take D for example. If free charge is absent, Maxwell's equations imply very nice equation div D = 0. The equation for E is more complicated (includes bound charge density that is hard to measure, hard to relate to other things in the model and so is usually preferred to be ignored).
If in addition the medium is linear (a special but important case), D is a simple linear function of E ( there is no such simple relation to charge density or current density) so things such as the concept of EM energy in medium is possible, and wave propagation in crystals can be analyzed most elegantly. Sure, all could be analyzed in terms of E and rho and j which would be more "physical" but it is not the most elegant way to do it. It is like in mechanics: we can analyze complicated systems with constraints by writing down many equations involving constraint forces, but there are easier methods such as the Lagrangian.
Note: In the following, I'll be using Lorentz-Heaviside units. For other unit systems, throw in factors of ε_0 or 4π as needed...
The reason for the introduction of D is that even though a medium may have no net charge, it's still made from protons and electrons, meaning the charge density will be nonzero. We call this the density of 'bound' charges ρ_b.
The medium is often modelled as consisting of tiny dipoles. If left to their own devices, the dipoles tend to align in such a way that the generated field largely cancels out.
Now, let's add additional charges via a density of 'free' charges ρ_f, yielding a total charge density ρ = ρ_f + ρ_b.
The bound charges will respond to the presence of the free charges, and the field they generate will no longer cancel out. We call this field -P, with P the electric polarization (the negative sign comes in through its definition as the dipole moment density of the dipole model).
Defining the electric displacement field as D = E + P, Gauss's law
div(E) = ρ
can be decomposed into
div(D) = ρ_f
and
div(P) = -ρ_b
In many cases, the response of the medium will be approximately linear, and polarization will be proportional to the field generated by the free charges, P = η·D. Note that the definition of P was such that for positive η, the actual field will be opposing D.
Equivalently, we can consider the response linear in the total field, P = χ·E if we introduce the electric susceptibility χ = η/(1-η).
For the displacement field, we get
D = E + P = (1 + χ)·E = ε·E
with ε the permittivity.
What's the point, you may ask? Simplification, as we can now just measure the linear response of the medium, instead of having to figure out the microscopic distribution of bound charges.
The reason for the introduction of D is that even though a medium may have no net charge, it's still made from protons and electrons, meaning the charge density will be nonzero. We call this the density of 'bound' charges ρ_b.
The medium is often modelled as consisting of tiny dipoles. If left to their own devices, the dipoles tend to align in such a way that the generated field largely cancels out.
Now, let's add additional charges via a density of 'free' charges ρ_f, yielding a total charge density ρ = ρ_f + ρ_b.
The bound charges will respond to the presence of the free charges, and the field they generate will no longer cancel out. We call this field -P, with P the electric polarization (the negative sign comes in through its definition as the dipole moment density of the dipole model).
Defining the electric displacement field as D = E + P, Gauss's law
div(E) = ρ
can be decomposed into
div(D) = ρ_f
and
div(P) = -ρ_b
In many cases, the response of the medium will be approximately linear, and polarization will be proportional to the field generated by the free charges, P = η·D. Note that the definition of P was such that for positive η, the actual field will be opposing D.
Equivalently, we can consider the response linear in the total field, P = χ·E if we introduce the electric susceptibility χ = η/(1-η).
For the displacement field, we get
D = E + P = (1 + χ)·E = ε·E
with ε the permittivity.
What's the point, you may ask? Simplification, as we can now just measure the linear response of the medium, instead of having to figure out the microscopic distribution of bound charges.
This is a pretty standard treatment. What remains unclear is whether E is what the free charges generate (and what brings the mysterious D into existence), or it is what acts on the probe charge (which is calculated from D).
E is generated by all charges:
Admittedly, things get muddled because the distinction E vs D does double duty: We also associate E with (specific) forces, and D with fluxes. Depending on your system of units, this necessitates the introduction of a conversion factor.
div(E) = ρ = ρ_f + ρ_b
div(D) = ρ_f
Admittedly, things get muddled because the distinction E vs D does double duty: We also associate E with (specific) forces, and D with fluxes. Depending on your system of units, this necessitates the introduction of a conversion factor.
I've been trying to understand the same thing: what those equations actually describe. So far I've come up with this analogy. The B field describes surface of the magnetic medium or substance of unknown origin, the E field is merely the apparent velocity of this surface. Electrons and other charged particles blindly run down the slopes of the magnetic medium. There's also this rot B and rot E part that creates vorticity, similar to what we see in liquids.
This sounds very much like the aether hypothesis of the 19th century which was abandoned since it is incompatible with many experimental observations, such as the Michelson-Morley experiment. The modern point of view is that EM fields are fundamental and have no underlying mechanism such as an aether medium or something like that.
Nah, that experiment disproved the "static background medium" within which the earth would be moving.
Sure, there are some loopholes like a dragged aether that could resolve the contradiction with Michelson-Morley. But you are going to have a very hard time explaining all the other tests of special relativity such as Ives-Stilwell type experiments.
It’s easy to understand, just grab some metal wires and a battery and
Abstract concepts that you can’t touch or see are hard.
Abstract concepts that you can’t touch or see are hard.
Simple: the arrows are backwards due to guessing at the direction before we knew which way the electrons went
Electrons aren't the only charge carriers. When you understand that, you'll understand why conventional current isn't backwards.
What are the other charge carriers?
> what are the other charge carriers?
Electrons flow in metals, but inside most non-metals, free electrons don't exist. For example:
Protons flow in acids. But chemists call protons "+H ions"
+Na and -Cl flow in salt water (and in damp ground.)
-OH negative ions flow in alkaline electrolytes
-OH, protons, +Na, -Cl, +K, and all sorts of charged molecules flow inside human bodies. (When you receive a shock, no electrons flowed through your body.)
Electrons and positive ions flow in spark-plasma, lightning and fluorescent tubes.
In liquid metals, electrons flow one way and positive metal ions flow the other. (So, only solid metal wires are purely electron-conductors.)
In moving wires, both protons and electrons are moving. But since the amperes are the difference between electron and proton flows, the motion of the metal doesn't create any current. (Note that electric current in wires isn't a flow of electrons, instead it's the difference between electron-flow and proton-flow.)
Also, look at the currents in salt water: positives flow one way, and negatives go backwards past them, in the same conductor. What then is the "true" direction of the current?
Electrons flow in metals, but inside most non-metals, free electrons don't exist. For example:
Protons flow in acids. But chemists call protons "+H ions"
+Na and -Cl flow in salt water (and in damp ground.)
-OH negative ions flow in alkaline electrolytes
-OH, protons, +Na, -Cl, +K, and all sorts of charged molecules flow inside human bodies. (When you receive a shock, no electrons flowed through your body.)
Electrons and positive ions flow in spark-plasma, lightning and fluorescent tubes.
In liquid metals, electrons flow one way and positive metal ions flow the other. (So, only solid metal wires are purely electron-conductors.)
In moving wires, both protons and electrons are moving. But since the amperes are the difference between electron and proton flows, the motion of the metal doesn't create any current. (Note that electric current in wires isn't a flow of electrons, instead it's the difference between electron-flow and proton-flow.)
Also, look at the currents in salt water: positives flow one way, and negatives go backwards past them, in the same conductor. What then is the "true" direction of the current?
Lack of electrons.
Or to say it a different way, protons without electrons.
Though I don't think protons get transferred over a wire.
Though I don't think protons get transferred over a wire.
Isn't this just a conceptual thing? It's still the electrons that are moving, and they're leaving "holes" behind so you can model either the electrons moving or the holes moving but there's still only one particle.
I agree with the top parent comment, I wish we had gotten the charge of electrons correct. I remember bandgap diagrams being confusing too because electrons basically roll "uphill" and felt like it would be easier to understand if we just called them positive.
I agree with the top parent comment, I wish we had gotten the charge of electrons correct. I remember bandgap diagrams being confusing too because electrons basically roll "uphill" and felt like it would be easier to understand if we just called them positive.
In P-type semiconductors, a small amount of impurity/doping produces "holes": http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/dope.html#...
Free electrons can temporarily occupy holes, then dislodge themselves and move on to the next place. But it will look like as if the holes are moving from one place to another.
Free electrons can temporarily occupy holes, then dislodge themselves and move on to the next place. But it will look like as if the holes are moving from one place to another.
They don't in metals but I don't think it would make any difference if they did.
This is now, officially, my absolute favorite article on HN(!), as of today's date.
I am not being sarcastic!
You see, I've had the same thoughts (about the many paradoxes in the existing knowledge of electricity) for a long, long time!
This article goes a long way towards challenging the "status quo" with respect to what is currently known and/or popularly believed about electricity...
It is well worth a reads and many re-reads, both now and in the future...
My absolute favorite article on HN, thus far!
I am not being sarcastic!
You see, I've had the same thoughts (about the many paradoxes in the existing knowledge of electricity) for a long, long time!
This article goes a long way towards challenging the "status quo" with respect to what is currently known and/or popularly believed about electricity...
It is well worth a reads and many re-reads, both now and in the future...
My absolute favorite article on HN, thus far!
Try the finished version! Those were just the unedited notes from 1988, and over later years I used them for a large number of articles and essays. http://amasci.com/miscon/elect.html is the big list of electricity misconceptions. The other articles are at http://amasci.com/ele-edu.html
Hi Bill (or do you prefer William?) Beaty!
Some excellent links!
But, you've always ran an excellent website since day one, a long time ago, to be sure!
Fun historical fact(!): One of the first articles I posted to HN a long time ago -- was your article on hand-drawn holograms!
I wouldn't have posted that... unless I thought you were on to some deeper principle, some deeper truth, something... in other words, there was something there...
Anyway, if you would like to connect via email and/or LinkedIn, I'm available at [email protected] and/or www.linkedin.com/in/peter-sherman-a6107a5
I think you'd find me a fascinating guy of your caliber...
Of course, if you'd rather not, and value your privacy, then I respect that too...
Some excellent links!
But, you've always ran an excellent website since day one, a long time ago, to be sure!
Fun historical fact(!): One of the first articles I posted to HN a long time ago -- was your article on hand-drawn holograms!
I wouldn't have posted that... unless I thought you were on to some deeper principle, some deeper truth, something... in other words, there was something there...
Anyway, if you would like to connect via email and/or LinkedIn, I'm available at [email protected] and/or www.linkedin.com/in/peter-sherman-a6107a5
I think you'd find me a fascinating guy of your caliber...
Of course, if you'd rather not, and value your privacy, then I respect that too...
It is a very complex phenomenon that can be best described with concepts that deal with aggregate matter taken from quantum chemistry/solid state physics (look up the transition from atom orbitals to molecular orbitals to bands). The classical electron hopping theory is a very primitive abstraction that suits a certain level of education.
I haven't read the article (yet) but skimmed it. I do think you're right, but I also think the average person's tools to observe it are lacking. Like Plato's Allegory of the Cave. If someone had never experienced something like bodies of water and tried to explain it would be much more difficult that observing and touching. An abstraction that breaks down very quickly, like electron hopping theory, makes it worse.
Is "electron hopping theory" same as the hopping transport mechanism in https://en.wikipedia.org/wiki/Charge_transport_mechanisms?
I'm trying to read up on it because I realized my knowledge about electricity is very basic (only first year physics lecture on electricity & Maxwell's equations).
I'm trying to read up on it because I realized my knowledge about electricity is very basic (only first year physics lecture on electricity & Maxwell's equations).
Site not working for me ATM. Maybe the "HN effect?" Anyway, here's the Google cache link if anyone needs it:
http://webcache.googleusercontent.com/search?q=cache:OX-NatS...
http://webcache.googleusercontent.com/search?q=cache:OX-NatS...
Reading this, I think I might have been confused about some of these concepts as well. But I had a hard time explaining them to myself.
I wonder, is there any resource online that explains electricity properly in a "for dummies" way? I'd be interested in going through it and seeing what surprises me.
I wonder, is there any resource online that explains electricity properly in a "for dummies" way? I'd be interested in going through it and seeing what surprises me.
This article is pretty good. A short summary is that electricity is like a sound wave propagating thru a sea of electrons or protons or something charged.
This is however the tip of the iceberg. The real mystery is how those electrons and protons feel each other. They don't bump into each other like atoms in the air, they interact via magnetic field - a mysterious medium that magically appears around charged particles and alters their trajectories. It's the same magnetic field that surrounds bar magnets. Rumors are magnetic field is made of photons, but nobody has been able to see or catch those photons, so they have been renamed into virtual photons. Those special photons don't really exist, but still interact with charges.
This is however the tip of the iceberg. The real mystery is how those electrons and protons feel each other. They don't bump into each other like atoms in the air, they interact via magnetic field - a mysterious medium that magically appears around charged particles and alters their trajectories. It's the same magnetic field that surrounds bar magnets. Rumors are magnetic field is made of photons, but nobody has been able to see or catch those photons, so they have been renamed into virtual photons. Those special photons don't really exist, but still interact with charges.
> This is however the tip of the iceberg. The real mystery is how those electrons and protons feel each other.
Is it any more mysterious then how our planet 'feels' the presence of the Sun, through the gravitational force, despite being 150,000,000 kilometers away?
Is it any more mysterious then how our planet 'feels' the presence of the Sun, through the gravitational force, despite being 150,000,000 kilometers away?
The two are very similar in this regard.
Do you consider the mechanism through which gravitational effects propagate mundane?
I mean, it is a magical field that seems to surround every single observable object (and some otherwise unobservable ones) that propagates at the speed of light. On that scale of weird, magnetism is not particularly special.
Magnetic field can be derived from electrostatic effects and special relativistic effects. That sounds complicated but both are sophomore level concepts. Sure, the electromagnetic force is mediated by photons, but you don’t need that piece of (graduate-level) knowledge to understand magnetism.
I personally absolutely need that piece of information. I have a simple assumption about the material universe. All interactions rely on touch. Atoms or their sub-particles don't magically interact with each other over a distance.
That's why I still don't understand gravitation, at all. I don't care that we can calculate something. That doesn't tell me what is actually happening.
That's why I still don't understand gravitation, at all. I don't care that we can calculate something. That doesn't tell me what is actually happening.
In a classical sense, no interactions rely on touch and atoms only interact with each other over a distance.
Just think of electricity of water flowing through a pipe. All the concepts are exactly the same.
Electrons = Water molecules
Battery = Water tank
Wire = Pipe
Load = Water mill
Voltage difference = How high tank is from water mill
Amps = Amount of water molecules flowing through pipe
Resistor = Pipe with sand
Electrons = Water molecules
Battery = Water tank
Wire = Pipe
Load = Water mill
Voltage difference = How high tank is from water mill
Amps = Amount of water molecules flowing through pipe
Resistor = Pipe with sand
The problem I have with this sort of popular water analogy is that I don't really have any better intuition on hydraulics or fluid mechanics than I have on electronics. Maybe this has been different in the past when the water analogy was introduced, but I don't see it being very useful at least today.
Let me try with just the analogy of a hose and your thumb.
Water is flowing out of the hose at some rate. If you put your thumb over the end of the hose, you can create a stream of water (of less volume) that shoots out a farther distance because of increased pressure (you can feel this pressure increase in your thumb).
Think of amps as the volume of water, and voltage as the pressure. Power is voltage times current, or pressure times volume of water.
You could squirt a stream of water many feet (raising the voltage), but it's not a very large quantity of water (amps). Conversely, with your thumb off the end of the hose, the pressure (volts) isn't very high (it just flows out at whatever your tap pressure is), but the volume of water is significant (amps).
Curious whether that is any clearer of an analogy?
Water is flowing out of the hose at some rate. If you put your thumb over the end of the hose, you can create a stream of water (of less volume) that shoots out a farther distance because of increased pressure (you can feel this pressure increase in your thumb).
Think of amps as the volume of water, and voltage as the pressure. Power is voltage times current, or pressure times volume of water.
You could squirt a stream of water many feet (raising the voltage), but it's not a very large quantity of water (amps). Conversely, with your thumb off the end of the hose, the pressure (volts) isn't very high (it just flows out at whatever your tap pressure is), but the volume of water is significant (amps).
Curious whether that is any clearer of an analogy?
The thumb is commonly used as an analogy for a resistor because it limits the current. But with the hosepipe it seems to increase the voltage, which a resistor does not do. What you describe (trading current for voltage) is more like a transformer.
Interesting. I spent a lot of time in my childhood playing with water in the sandbox, perhaps that made the analogy more real.
For me it was playing Pipe Mania [0][1].
[0] https://en.wikipedia.org/wiki/Pipe_Mania [1] https://archive.org/details/win3_PipeDr3x
[0] https://en.wikipedia.org/wiki/Pipe_Mania [1] https://archive.org/details/win3_PipeDr3x
so I guess water in a sandbox is the hydraulic analogy version of scuffing your feet on a shag carpet?
One important difference is that for water we have gravity which is geographically directional at earthly human scales. So "high up" isn't as intuitively visualizable for electric circuits, unless you carefully arrange components so that distance is correlated to voltage.
I don't think voltage is adequately explained like that. It doesn't matter how high a tank of water is, the force pushing it down is exactly the same. I think instead you need to use a pump which can vary the pressure.
The height of the pump increases the distance that the force will do work over (or how much kinetic energy the force will impart to a molecule), akin to how voltage will impart kinetic energy to the electron.
Potential energy due to gravity is mgh. A pump adds more force to g. A tower increases h.
What's nice about the pump is that it removes the special spatial directionality of gravity. In electricity, Earth is a voltage point-of- reference but not a spatial directional reference for computing forces.
Potential energy due to gravity is mgh. A pump adds more force to g. A tower increases h.
What's nice about the pump is that it removes the special spatial directionality of gravity. In electricity, Earth is a voltage point-of- reference but not a spatial directional reference for computing forces.
The pressure of water at the bottom of a pipe is directly related to the height of the pipe (the term used is "head"). A higher tank means higher pressure.
Sadly, this article does not really help you understand what electricity is. But I guess if you already know what it is in a wrong way you can read it and get some sort of negative feedback and, perhaps, get some epiphany about what it really is (or, isn't).
I was hoping for something to an article helping you understand. A list of things is it not helps, but only somewhat.
I was hoping for something to an article helping you understand. A list of things is it not helps, but only somewhat.
Agreed. This collection of articles appears to be a mix of ranting about misconceptions and giving factoids, randomly marking them as misconceptions or as what's really happening. If you were not confused before reading any of it (I was not), chances are, you will be afterwords (I was).
This is the exact opposite of good pedagogy. Ironic, since it's supposedly aimed at educators.
This is the exact opposite of good pedagogy. Ironic, since it's supposedly aimed at educators.
It's not a collection of articles. Read the first line. It's raw notes, random musings, and uninspected WRONG CRAP scribbled out of order, on random bits of paper. In crayon.
> If you were not confused before reading any of it
If you watch discarded film-clips, all two seconds long and many of them backwards, expect to be confused.
The actual articles are at http://amasci.com/ele-edu.html
> If you were not confused before reading any of it
If you watch discarded film-clips, all two seconds long and many of them backwards, expect to be confused.
The actual articles are at http://amasci.com/ele-edu.html
I agree with most of the comments here.
The article dies little if anything to help K6 educators (or students) understand electricity.
I think K6 should teach something good along the lines of safety/fun, and 6-12 something along the lines of practicality.
I learned Ohm's law when I was about 10 via "multi-kits" like so many other kids of my generation. This basic knowledge of electricity has served me well over the decades. It is seldom taught in school. Why?
I still don't really understand Maxwell's equations, but neither does your average electrician. That doesn't mean your average electrian doesn't have more knowledge about practical electricity than your average scientist who does understand Maxwell.
The article dies little if anything to help K6 educators (or students) understand electricity.
I think K6 should teach something good along the lines of safety/fun, and 6-12 something along the lines of practicality.
I learned Ohm's law when I was about 10 via "multi-kits" like so many other kids of my generation. This basic knowledge of electricity has served me well over the decades. It is seldom taught in school. Why?
I still don't really understand Maxwell's equations, but neither does your average electrician. That doesn't mean your average electrian doesn't have more knowledge about practical electricity than your average scientist who does understand Maxwell.
It's not an article. Read the first line.
The finished article(s) are listed at http://amasci.com/ele-edu.html
And heh, about maxwell, if someone claims to understand Maxwell's Equations, just sadly shake your head, then adopt an archly superior stance, and haughtily inform them that those four are HEAVISIDE'S equations, while Maxwell's were twenty equations based on the latest 1800s math-fad: Hamilton's "quaternions." If they don't understand THOSE, they don't understand Maxwell! (And now we've avoided having to admit we've never read any of them. Hee!)
The finished article(s) are listed at http://amasci.com/ele-edu.html
And heh, about maxwell, if someone claims to understand Maxwell's Equations, just sadly shake your head, then adopt an archly superior stance, and haughtily inform them that those four are HEAVISIDE'S equations, while Maxwell's were twenty equations based on the latest 1800s math-fad: Hamilton's "quaternions." If they don't understand THOSE, they don't understand Maxwell! (And now we've avoided having to admit we've never read any of them. Hee!)
It's not an article. It's not supposed to explain anything. Read the first line. It's a wad of notes, a bunch of totally-unedited crap scribbled on napkins in 1988, while THINKING about writing a proper article.
For those who didn't read:
"BELOW are my original, very crude and totally unedited 1986-1989 notes and "raw data" for...
My actual completed Electricity articles are: http://amasci.com/ele-edu.html
For those who didn't read:
"BELOW are my original, very crude and totally unedited 1986-1989 notes and "raw data" for...
My actual completed Electricity articles are: http://amasci.com/ele-edu.html
To truly understand electricity you have to understand the Maxwell equations. No amount of analogies using water can change that.
(Why the downvotes? Is math truly that scary for a forum of software engineers?)
(Why the downvotes? Is math truly that scary for a forum of software engineers?)
Are Maxwell's equations useful? Electric wires are very unlike the situations you deal with in an electromagnetics class, and conversely there are phenomena no electrical engineer ever thinks about, like the fact that a voltage drop over a resistor means there's a nonzero charge distribution at its ends, and similarly surface charges on the wire have to carefully redistribute themselves around bends in the wire to guide the electrons along it. Unless you work with gigahertz electronics, none of the interesting electrodynamic transient behavior matters either, the circuit always instantly finds the steady state distribution.
That the water analogy works so well also has little to do with the Maxwell equations, if I'm not mistaken, I think it has more to do with the conduction electrons behaving more or less like a (highly degenerate) gas.
That the water analogy works so well also has little to do with the Maxwell equations, if I'm not mistaken, I think it has more to do with the conduction electrons behaving more or less like a (highly degenerate) gas.
The water analogy works because circuits are linear systems. Pretty much all linear systems can be modeled that way, if you're willing to contort things the right way.
Water analogy works well even with non-linear components like diodes (think one-way valve) and transistors (think valve controlled by water pressure from separate tube).
Works other way too. For me the explanation of a hydraulic ram pump[1] clicked when I realized it's essentially just like a boost converter[2].
[1]: https://en.wikipedia.org/wiki/Hydraulic_ram
[2]: https://en.wikipedia.org/wiki/Boost_converter
[1]: https://en.wikipedia.org/wiki/Hydraulic_ram
[2]: https://en.wikipedia.org/wiki/Boost_converter
For a layperson, Ohm's law and Kirchhoff's laws suffice.
You don't need curl and divergence to figure out whether you can turn on your microwave and coffee maker at the same time without tripping the circuit breaker.
You don't need curl and divergence to figure out whether you can turn on your microwave and coffee maker at the same time without tripping the circuit breaker.
This is only true because someone who did understand the more complicated principles designed the appliances in question. High voltage and high frequency are where the most common and intuitive understanding of electricity break down. Anything above about a megahertz or a few hundred volts and you will start to see relatively strange things happen.
My point is that few people work with high frequencies.
For most practical tasks, even the fact that we're working with AC rather than DC can be glossed over. People can plug in 120 V into Ohm's law and get the right result even though actual voltage fluctuates between -170 V and +170 V.
For most practical tasks, even the fact that we're working with AC rather than DC can be glossed over. People can plug in 120 V into Ohm's law and get the right result even though actual voltage fluctuates between -170 V and +170 V.
It seems clear to me that this article is aimed at science educators who do have a solid understanding of electromagnetism, electronics, etc., but struggle to teach high-school and college-aged students due to widespread misconceptions about “electricity” (some of which seem bizarre to an expert). The article explains what those misconceptions are because it is assuming the reader would quickly understand the scientific (or ontological) error and spend the bulk of their thought on the educational side.
This article is simply not aimed at you, it is directed towards experts. So your complaint is a bit like complaining that “C# In Depth” doesn’t sufficiently explain basic syntax.
This article is simply not aimed at you, it is directed towards experts. So your complaint is a bit like complaining that “C# In Depth” doesn’t sufficiently explain basic syntax.
[deleted]
Love this article. I wonder if this is a brain-type thing. It really rings true for me.
Developing the idea, I have a similar multiple definitions problem, in a much smaller context, with the word “prescription”.
In the UK it means all of: a doctor’s idea of what medicine to give to a patient, a piece of paper with that written on it, and the medicine itself.
I got thoroughly confused when I went to collect a prescription from a pharmacy and was told “it’s (still) over at the surgery”. It wasn’t, or rather, it was. But we were talking about different prescriptions.
Anyone else have these (pedantic?) confusions?
Developing the idea, I have a similar multiple definitions problem, in a much smaller context, with the word “prescription”.
In the UK it means all of: a doctor’s idea of what medicine to give to a patient, a piece of paper with that written on it, and the medicine itself.
I got thoroughly confused when I went to collect a prescription from a pharmacy and was told “it’s (still) over at the surgery”. It wasn’t, or rather, it was. But we were talking about different prescriptions.
Anyone else have these (pedantic?) confusions?
“Meter” is multiply overloaded. A unit of distance. A thing that makes measurements. An adjustment to a rate of flow.
“Extrusion” is a process as well as the object resulting from that process.
“By referencing the meter and adjusting the metering valve during extrusion, we can create a precisely meter long extrusion.”
Micrometer is a unit of measurement and measurement device that measures in that range, but often measures in thousands of an inch, which are commonly called “mills”, which is also the act of a type of machining and the name of the machinery that does it as well as the name of a common type of cutting tool that goes into that machine.
“Put an end mill in the mill and mill off five mills.”
“Extrusion” is a process as well as the object resulting from that process.
“By referencing the meter and adjusting the metering valve during extrusion, we can create a precisely meter long extrusion.”
Micrometer is a unit of measurement and measurement device that measures in that range, but often measures in thousands of an inch, which are commonly called “mills”, which is also the act of a type of machining and the name of the machinery that does it as well as the name of a common type of cutting tool that goes into that machine.
“Put an end mill in the mill and mill off five mills.”
> “Meter” is multiply overloaded. A unit of distance. A thing that makes measurements. An adjustment to a rate of flow.
There is "meter" and there is "metre".
> “Put an end mill in the mill and mill off five mills.”
* https://en.wikipedia.org/wiki/Buffalo_buffalo_Buffalo_buffal...
There is "meter" and there is "metre".
> “Put an end mill in the mill and mill off five mills.”
* https://en.wikipedia.org/wiki/Buffalo_buffalo_Buffalo_buffal...
I guess "prescription" refers directly to your first definition but can also refer to the two other ones by metonymy [0].
[0] https://en.wikipedia.org/wiki/Metonymy
[0] https://en.wikipedia.org/wiki/Metonymy
I love these articles and posted a link to them on a HN article a few weeks ago in response to a statement about the power company producing electrons.
I've only skimmed the top of this so far but the bit about AC vs DC rings true for me. I'm just getting into electronics and I just couldn't understand what capacitors did. I watched all the water membrane videos and it all made sense, but what could it do? It clicked when I realised I had until this point separated all electricity into AC and DC and in my mind my electronics project was DC! I was confused because a capacitor seems like an open circuit, which it is (at DC). I didn't even allow the possibility of considering that there is AC on my circuit. But that's the entire point of electronics. Transistors and other components allow you to switch current on and off, hence AC.
Now it has clicked I intuitively understand how things like bypass capacitors work. But I don't think I could explain it well enough to teach it. It seems like it it doesn't click for you you'll never be able to do electronics.
I noticed in The Art of Electronics they don't capitalise ac and dc. I wonder if that is to escape the popular ideas of the capitalised AC and DC? I looked but couldn't find an explanation in the book.
Now it has clicked I intuitively understand how things like bypass capacitors work. But I don't think I could explain it well enough to teach it. It seems like it it doesn't click for you you'll never be able to do electronics.
I noticed in The Art of Electronics they don't capitalise ac and dc. I wonder if that is to escape the popular ideas of the capitalised AC and DC? I looked but couldn't find an explanation in the book.
It might have been easier to understand if Benjamin Franklin had used the correct polarity for electrons.
He made the proton positive, and the electrons negative. But this mistake became a historical embarrassment, but ultimately stuck, because the world was too entrenched in it.
Instead, he should’ve made the proton as negative, and the electron as positive. Intuitively, this may have helped people understand how electricity flows better.
An alien extraterrestrial society in a distant galaxy would probably be wondering why we have our electricity signs all backwards.
Such as: why must we disconnect the negative cable from our car battery first?
He made the proton positive, and the electrons negative. But this mistake became a historical embarrassment, but ultimately stuck, because the world was too entrenched in it.
Instead, he should’ve made the proton as negative, and the electron as positive. Intuitively, this may have helped people understand how electricity flows better.
An alien extraterrestrial society in a distant galaxy would probably be wondering why we have our electricity signs all backwards.
Such as: why must we disconnect the negative cable from our car battery first?
I'm not sure flipping the assignments would have helped with understanding the flow of electrical energy. It might even re-enforce the common misconceptions being outlined in the article here.
One, electrical energy does not flow from cathode to anode. Nor does it go the other way. The energy goes down both wires, from source to load.
Two, it's an arbitrary decision if you want to talk about negative charges going east, or positive charges going west. They're equivalent when talking about a net-neutral wire.
There are a lot of symmetries in the world that we break by arbitrary convention. The polarity of subatomic particles, the right-hand rule used in vector mathematics, the way bolts are threaded.
The alien society might just use a "left-hand rule" for their magnetism and vector operations, and have clocks that turn opposite of ours (which probably means their planet orbits the opposite way?)
As far as car batteries go, the reason to disconnect the (–) first is because it's almost always* the chassis ground. If you were to work on an ancient Volkswagen, then you'd be told to disconnect the (+) cable first. Disconnecting the other terminal first is more dangerous; your wrench is a perfect short circuiting tool!
* And the reason we all use negative for chassis ground has to do with galvanic corrosion, I think?
One, electrical energy does not flow from cathode to anode. Nor does it go the other way. The energy goes down both wires, from source to load.
Two, it's an arbitrary decision if you want to talk about negative charges going east, or positive charges going west. They're equivalent when talking about a net-neutral wire.
There are a lot of symmetries in the world that we break by arbitrary convention. The polarity of subatomic particles, the right-hand rule used in vector mathematics, the way bolts are threaded.
The alien society might just use a "left-hand rule" for their magnetism and vector operations, and have clocks that turn opposite of ours (which probably means their planet orbits the opposite way?)
As far as car batteries go, the reason to disconnect the (–) first is because it's almost always* the chassis ground. If you were to work on an ancient Volkswagen, then you'd be told to disconnect the (+) cable first. Disconnecting the other terminal first is more dangerous; your wrench is a perfect short circuiting tool!
* And the reason we all use negative for chassis ground has to do with galvanic corrosion, I think?
> One, electrical energy does not flow from cathode to anode. Nor does it go the other way. The energy goes down both wires, from source to load.
And it doesn't even "do gown" "the wires" depending on what you mean by that. The energy flux is IIRC the product of E and B fields, which is non-zero only outside the wires.
The wires, in a sense, only acts as a rough guide for the energy, which itself is transmitted through the air/non-conducting surrounding space, and (importantly for some applications) enters the load from its "sides", from the non-conducting space around it, not through the wires.
And it doesn't even "do gown" "the wires" depending on what you mean by that. The energy flux is IIRC the product of E and B fields, which is non-zero only outside the wires.
The wires, in a sense, only acts as a rough guide for the energy, which itself is transmitted through the air/non-conducting surrounding space, and (importantly for some applications) enters the load from its "sides", from the non-conducting space around it, not through the wires.
The insulators are the conductors :o
hey if there's anyone who understands this:
> ELECTRIC ENERGY is a wave that travels via a column of charge.
what's a "column of charge", and where could i read more about those (preferably online)? i found the term ungoogle-able – i keep getting stuff with "coulomb" instead. (and i'm assuming it's not a typo)
> ELECTRIC ENERGY is a wave that travels via a column of charge.
what's a "column of charge", and where could i read more about those (preferably online)? i found the term ungoogle-able – i keep getting stuff with "coulomb" instead. (and i'm assuming it's not a typo)
The column of charge inside a metal wire is usually called "metallic electron-sea" or "sea of charge."
In other words, all metals are always full of electron-fluid. They're like plumbing pipes, but pipes which are pre-filled with water, with no bubbles allowed. During an electric current, it's the wires' own electrons which begin flowing. (A long thin column of copper is always a long thin column of movable electric charge. So, hook it in a circle, and that creates an invisible "electron flywheel.")
See the completed article: http://amasci.com/miscon/elect.html, a big list of common misconceptions.
In other words, all metals are always full of electron-fluid. They're like plumbing pipes, but pipes which are pre-filled with water, with no bubbles allowed. During an electric current, it's the wires' own electrons which begin flowing. (A long thin column of copper is always a long thin column of movable electric charge. So, hook it in a circle, and that creates an invisible "electron flywheel.")
See the completed article: http://amasci.com/miscon/elect.html, a big list of common misconceptions.
He has a number of articles. He calls this one "Raw, Un-edited notes ...", which I think suggest reading for a link to a finished version. One such link in the article is this: http://amasci.com/miscon/whatis.html
what's a "column of charge"
It's an analogy, providing a correspondence between a column of fluid and a column of charge (the 'electric fluid').
It's an analogy, providing a correspondence between a column of fluid and a column of charge (the 'electric fluid').
If you find yourself struggling to understand the basic concepts of electricity, I can warmly recommend the book "There are no electrons" by Kenn Amdahl. It's a very silly book, which attempts to explain electricity through allegory and humour
THERE ARE NO ELECTRONS is incredibly excellent.
Another is Darren Ashby's "Electrical Engineering 101: Everything You Should Have Learned in School...but Probably Didn't"
ALSO SEE:
Are we teaching electricity the wrong way 'round? http://www.abc.net.au/science/articles/2014/02/05/3937083.ht...
Understanding electricity and circuits: what textbooks don't tell you http://web.archive.org/web/20080730063549/science.uniserve.e...
FIELDS OF ELECTRONICS: understanding circuits via physics https://onlinelibrary.wiley.com/doi/book/10.1002/0471433934
Another is Darren Ashby's "Electrical Engineering 101: Everything You Should Have Learned in School...but Probably Didn't"
ALSO SEE:
Are we teaching electricity the wrong way 'round? http://www.abc.net.au/science/articles/2014/02/05/3937083.ht...
Understanding electricity and circuits: what textbooks don't tell you http://web.archive.org/web/20080730063549/science.uniserve.e...
FIELDS OF ELECTRONICS: understanding circuits via physics https://onlinelibrary.wiley.com/doi/book/10.1002/0471433934
That looks extremely interesting - I see so many people misled by electron misconceptions.
It really is. Though I guess I should clarify that it gives you practical understanding of electricity and the basics of electronics. Working knowledge, as it were. It won't teach you about the actual physics of electricity. Kind of like how you can learn downhill skiing without understanding Newton or Einstein.
I have that book, and agree, it's fantastic.
Thanks! I can't stop reading.
Love this article. As a former EE ( been in software too long and never actually worked as an EE LOL ), demystifying common misconceptions about a subject is a great way to get people to build a better mental model. Wish more educators would do this in college/university.
But, if you don’t read the whole article, do read this tidbit.
“ ...little use by educators of the wind/sound electrical analogy:
AIR is a physical substance.
SOUND is a wave that propagates rapidly through a volume of air.
WIND is a flowing motion of air already present.
—-
ELECTRIC CHARGES are a physical substance.
ELECTRIC ENERGY is a wave that travels via a column of charge.
ELECTRIC CURRENT is a flowing motion of the charge already present.
—-
The confusion between charge-flow and energy-flow is similar to confusion between wind versus sound. Do you know that sound is not wind? To believe that electrons flow at the speed of light is similar to believing that air must travel at 720mph out of your mouth to distant ears. “
But, if you don’t read the whole article, do read this tidbit.
“ ...little use by educators of the wind/sound electrical analogy:
AIR is a physical substance.
SOUND is a wave that propagates rapidly through a volume of air.
WIND is a flowing motion of air already present.
—-
ELECTRIC CHARGES are a physical substance.
ELECTRIC ENERGY is a wave that travels via a column of charge.
ELECTRIC CURRENT is a flowing motion of the charge already present.
—-
The confusion between charge-flow and energy-flow is similar to confusion between wind versus sound. Do you know that sound is not wind? To believe that electrons flow at the speed of light is similar to believing that air must travel at 720mph out of your mouth to distant ears. “
Beautiful comment. The articles were getting panned, so I was going to skip them, but now I won’t.
Not articles, just crude notes FOR articles elsewhere on the site. I keep changing the name of this ancient 1980s txt file, but people keep re-posting it!
Try the finished versions instead:
List of electricity articles http://amasci.com/ele-edu.html
List of typical electricity misconceptions http://amasci.com/miscon/elect.html
Try the finished versions instead:
List of electricity articles http://amasci.com/ele-edu.html
List of typical electricity misconceptions http://amasci.com/miscon/elect.html
These articles are terrible.
Quote: "Scuff across a rug, and you charge your body to several thousand volts." Pardon me?
Further down: "Can an object have a certain voltage? No. Why not?" How does that fly with the above statement?
These articles are exactly the confusing non-pedagogical and partially straight out incorrect nonsense that the author criticises in other works.
Quote: "Scuff across a rug, and you charge your body to several thousand volts." Pardon me?
Further down: "Can an object have a certain voltage? No. Why not?" How does that fly with the above statement?
These articles are exactly the confusing non-pedagogical and partially straight out incorrect nonsense that the author criticises in other works.
I mean that sort of just proves the point doesn’t it? The terms are all so context sensitive and overlapping that even while explaining the issues it’s a struggle to not fall into the traps.
These aren't articles. READ THE FIRST LINE. They're random crude notes, scribbled down in 1988, and UNEDITED, so full of all sorts of horrible mistakes (that's what "unedited notes" means.)
The actual completed articles were written years later, many were even inspected/corrected by the phys-L group of college physics educators. http://amasci.com/ele-edu.html
The actual completed articles were written years later, many were even inspected/corrected by the phys-L group of college physics educators. http://amasci.com/ele-edu.html
> ...mistaken belief that energy flows out of a battery through one wire, then flows back through the other. The charges do this, while instead the energy flows along both wires in one direction, from source to load.
Has somebody a good visual analogy for this in another medium? I mean I know that this is a case but I can not visualize the energy flowing on both sides out of the source with the medium only moving out on one side.
I will try for myself:
Say I pump a lot of water in a circle by moving a pump by hand. I put some energy into the system. By pumping I push water molecues out one side of the pump and pulling them in on the other side. That creates a pressure difference inside the water. Even if I pump the water really slow, that pressure difference propagte with the speed of sound through the water. That pressure difference is positive one the one side of the pump (water is pushed) and negative on the other side (water is pulled). Somewhere on the other side of the pipe circle the pressure differences meet cancel each other out. So the pressure difference is the energy moving through the system in both directions. But the water itself only moves in one direction. But now we have two kinds if energy in the system. The pressure wave and the kinetic energy of the water. If I keep pumping the water will speed up faster and faster. I guess that's the analog to a glowing wire. But if a put a turbine into the water the flow of water will be slowed down because the kinetic energy of the water is extracted by the turbine. Now if the water is at rest and the turbine as well and I now start pumping the pressure difference will flow in both directions to the turbine. It will start spinning as soon as the pressure differences meet there. If the turbine is not opposite to the pump the pressure differences will take different amounts of time to reach it. But the turbine will already start moving when hit by the first pressure difference by absorbing it the (pressure wave stops there) and then latter be hit by opposite pressure difference and move again.
So far correct?
So in an ideal system the water would not move at all but only the pressure difference would propagate and be consumed by the turbine. But that would mean that the turbine energy leaves the system completely -> the turbine does not even turn because it's energy is 100% extracted by it's consumer.
So in this example flowing water always represents some kind of loss/inefficency. The goal would be to maximize the pressure difference to propagate but the minimze the water flowing.
Is this how you could explain alternating current for transportation of energy?
Has somebody a good visual analogy for this in another medium? I mean I know that this is a case but I can not visualize the energy flowing on both sides out of the source with the medium only moving out on one side.
I will try for myself:
Say I pump a lot of water in a circle by moving a pump by hand. I put some energy into the system. By pumping I push water molecues out one side of the pump and pulling them in on the other side. That creates a pressure difference inside the water. Even if I pump the water really slow, that pressure difference propagte with the speed of sound through the water. That pressure difference is positive one the one side of the pump (water is pushed) and negative on the other side (water is pulled). Somewhere on the other side of the pipe circle the pressure differences meet cancel each other out. So the pressure difference is the energy moving through the system in both directions. But the water itself only moves in one direction. But now we have two kinds if energy in the system. The pressure wave and the kinetic energy of the water. If I keep pumping the water will speed up faster and faster. I guess that's the analog to a glowing wire. But if a put a turbine into the water the flow of water will be slowed down because the kinetic energy of the water is extracted by the turbine. Now if the water is at rest and the turbine as well and I now start pumping the pressure difference will flow in both directions to the turbine. It will start spinning as soon as the pressure differences meet there. If the turbine is not opposite to the pump the pressure differences will take different amounts of time to reach it. But the turbine will already start moving when hit by the first pressure difference by absorbing it the (pressure wave stops there) and then latter be hit by opposite pressure difference and move again.
So far correct?
So in an ideal system the water would not move at all but only the pressure difference would propagate and be consumed by the turbine. But that would mean that the turbine energy leaves the system completely -> the turbine does not even turn because it's energy is 100% extracted by it's consumer.
So in this example flowing water always represents some kind of loss/inefficency. The goal would be to maximize the pressure difference to propagate but the minimze the water flowing.
Is this how you could explain alternating current for transportation of energy?
> Has somebody a good visual analogy for this in another medium? I mean I know that this is a case but I can not visualize the energy flowing on both sides out of the source with the medium only moving out on one side.
Imagine that for some insane reason, you set up a pipe underwater. On one end of the pipe you put a pump that pushes water into the pipe. At the other end of the pipe, you put a vacuum that sucks water out. In the middle of it, you put a turbine that powers a lightbulb. When you turn it on, energy flows from the pump to the turbine because the pump pushes the water. Energy also flows from the vacuum to the turbine because it sucks water out.
Batteries work like that, but with electrons as the medium. Negatively charged particles repel electrons, and positively charged ones attract it. So when you make a circuit, the negative terminal pushes electrons away from it and the positive terminal pulls them, resulting in both sides giving energy to the load.
> Is this how you could explain alternating current for transportation of energy?
This part I don't grasp super well, but I'll take a stab. It's a higher level thing. Resistive losses are relative to the current squared. So you want low current. But you need to deliver a lot of power, so you have to raise the voltage. Normal people's homes can't handle 200,000V power, so you have to convert it back to a lower voltage before you put it in people's homes. The cheapest/easiest way to do that is with a transformer, which requires a varying current (i.e. no DC).
Imagine that for some insane reason, you set up a pipe underwater. On one end of the pipe you put a pump that pushes water into the pipe. At the other end of the pipe, you put a vacuum that sucks water out. In the middle of it, you put a turbine that powers a lightbulb. When you turn it on, energy flows from the pump to the turbine because the pump pushes the water. Energy also flows from the vacuum to the turbine because it sucks water out.
Batteries work like that, but with electrons as the medium. Negatively charged particles repel electrons, and positively charged ones attract it. So when you make a circuit, the negative terminal pushes electrons away from it and the positive terminal pulls them, resulting in both sides giving energy to the load.
> Is this how you could explain alternating current for transportation of energy?
This part I don't grasp super well, but I'll take a stab. It's a higher level thing. Resistive losses are relative to the current squared. So you want low current. But you need to deliver a lot of power, so you have to raise the voltage. Normal people's homes can't handle 200,000V power, so you have to convert it back to a lower voltage before you put it in people's homes. The cheapest/easiest way to do that is with a transformer, which requires a varying current (i.e. no DC).
Maybe you're missing a key part: all wires are already full of electricity (full of electrons.) When a current starts up, it's the wires' electrons which start moving. In a circuit, no electricity is created and no electricity is destroyed, instead it just flows around in a complete circle.
So, when energy moves from a battery and flows outwards on both wires, also the "medium" is flowing inwards on one wire, outwards on the other.
An electric circuit is like a leather drive-belt. A generator is like a pulley.
When we force the pulley to turn, the entire drive-belt must turn also. The electrons are the leather, and they go slowly in a circle. But the "work" or the "horsepower" zips instantly along the belt, moving fast as the belt moves slow.
And, if we WIGGLE the first pulley, the belt also wiggles back and forth. Yet the "work" only flys outwards from the pulley, zooming off into the distance, regardless of which way the belt is turning.
So, when energy moves from a battery and flows outwards on both wires, also the "medium" is flowing inwards on one wire, outwards on the other.
An electric circuit is like a leather drive-belt. A generator is like a pulley.
When we force the pulley to turn, the entire drive-belt must turn also. The electrons are the leather, and they go slowly in a circle. But the "work" or the "horsepower" zips instantly along the belt, moving fast as the belt moves slow.
And, if we WIGGLE the first pulley, the belt also wiggles back and forth. Yet the "work" only flys outwards from the pulley, zooming off into the distance, regardless of which way the belt is turning.
That seems reasonable - a hydraulic system has to have a low pressure return. Your "pressure waves" correspond to the EM field waves that carry data signals; you get one in a DC circuit when you make or break a connection.
> Is this how you could explain alternating current for transportation of energy?
It seems like a reasonable model for DC. For AC you have to account for the repeated change in direction, which just looks odd in a hydraulic system because the medium has so much inertia.
> Is this how you could explain alternating current for transportation of energy?
It seems like a reasonable model for DC. For AC you have to account for the repeated change in direction, which just looks odd in a hydraulic system because the medium has so much inertia.
Dielectricity + magnetism in space and counter space.
https://youtu.be/TttHkDRuyZw
Enjoy the talk!
https://youtu.be/TttHkDRuyZw
Enjoy the talk!
Actually, electricity is so easy to understand that mathematicians are thrilled when they get to use electricity as a metaphor to gain insights into more abstract systems. The poster child for this approach would be the spectacular book:
Probability on Trees and Networks by Russell Lyons and Yuval Peres https://rdlyons.pages.iu.edu/prbtree/
As a comment on the style of "Why is electricity so hard to understand?", mathematicians get inundated with crank missives claiming simpler proofs of Fermat's Last Theorem, and many other hard problems. On one hand we try not to judge the delusion, as it takes a certain amount of delusion for any of us to find the confidence to overturn old ideas. Yet there's a balance here. With cell phones, the ability to self-rescue in the woods has gotten lost. Even the most delusional serious mathematician knows how to "self-rescue". Part of commanding one's work is understanding it in context, and to see how one might critique it, more incisively than any potential reader. This is not unique to math; "writer's block" is a writer losing control of this balance, just as insanity is anyone losing control of their inner chaos.
"Why is electricity so hard to understand?" is indulgent; it doesn't even try not to read like a crank missive.
I often reply to crank missives with advice on how not to be immediately coded as such. The world would be more fun if we were unable to tell the crazies apart from everyone else. Alas this advice rarely takes.
Probability on Trees and Networks by Russell Lyons and Yuval Peres https://rdlyons.pages.iu.edu/prbtree/
As a comment on the style of "Why is electricity so hard to understand?", mathematicians get inundated with crank missives claiming simpler proofs of Fermat's Last Theorem, and many other hard problems. On one hand we try not to judge the delusion, as it takes a certain amount of delusion for any of us to find the confidence to overturn old ideas. Yet there's a balance here. With cell phones, the ability to self-rescue in the woods has gotten lost. Even the most delusional serious mathematician knows how to "self-rescue". Part of commanding one's work is understanding it in context, and to see how one might critique it, more incisively than any potential reader. This is not unique to math; "writer's block" is a writer losing control of this balance, just as insanity is anyone losing control of their inner chaos.
"Why is electricity so hard to understand?" is indulgent; it doesn't even try not to read like a crank missive.
I often reply to crank missives with advice on how not to be immediately coded as such. The world would be more fun if we were unable to tell the crazies apart from everyone else. Alas this advice rarely takes.
"Why is electricity so hard to understand" has a first line.
It tells you that it's not an article. It's a crapload of unedited notes I scribbled down in random order on little scraps of paper back in 1988. You complain it has no style? IT'S NOT FOR OTHERS TO READ! (I keep hiding the file to avoid this problem, changing the filename, but people keep finding it and re-posting it here.)
Since 1988, the vast unedited garbage-pile I later used to write some actual articles, see the index: http://amasci.com/ele-edu.html THOSE I invite everyone to critique.
Some of them tend to enrage people, because:
- Problems worthy of attack, prove their worth by fighting back. - Piet Hein.
I find that people having long-standing physics misconceptions will fight like fury to preserve them against change. In the present case, my misconceptions-list was inspected by the Phys-L educators forum in the 1990s, for comment and critique (and numerous flaws repaired. But NOTE of those changes appear in whyhard2.html)
> with advice on how not to be immediately
My advice: read the friggin' first line! Here, I'll edit it to make it even clearer:
"BELOW are my original, very crude disorganized and totally unedited 1986-1989 notes and "raw data" collected on little scraps of paper for...
It tells you that it's not an article. It's a crapload of unedited notes I scribbled down in random order on little scraps of paper back in 1988. You complain it has no style? IT'S NOT FOR OTHERS TO READ! (I keep hiding the file to avoid this problem, changing the filename, but people keep finding it and re-posting it here.)
Since 1988, the vast unedited garbage-pile I later used to write some actual articles, see the index: http://amasci.com/ele-edu.html THOSE I invite everyone to critique.
Some of them tend to enrage people, because:
- Problems worthy of attack, prove their worth by fighting back. - Piet Hein.
I find that people having long-standing physics misconceptions will fight like fury to preserve them against change. In the present case, my misconceptions-list was inspected by the Phys-L educators forum in the 1990s, for comment and critique (and numerous flaws repaired. But NOTE of those changes appear in whyhard2.html)
> with advice on how not to be immediately
My advice: read the friggin' first line! Here, I'll edit it to make it even clearer:
"BELOW are my original, very crude disorganized and totally unedited 1986-1989 notes and "raw data" collected on little scraps of paper for...
I think he does an excellent job of explaining why it's so hard to explain this type of thing.