# Electrical energy

1. Jul 23, 2011

### tushar gupta

Does electrical energy reside in kinetic energy of electrons?

2. Jul 23, 2011

### Staff: Mentor

No. At least not a significant amount in ordinary circuits.

Last edited: Jul 23, 2011
3. Jul 23, 2011

### gsal

hhhmmm, never quite occur to me to look at it that way...

but now that you mention it, maybe it is better to equate electrical energy to some kind of potential energy, though, not kinetic...after all, when you get some work out of some electrical device through which a bunch of electrons are going by (or back and forth), the electrons actually do not loose any speed!

so, the energy pushing the electrons is some potential energy behind them...in a toy that works on batteries, the electrons are pushed by some chemical potential energy stored in the battery...at home, the potential energy is the voltage, etc.

does this make sense?

4. Jul 24, 2011

### tushar gupta

you said that electrons donot lose speed.but i thought the moving electrons collide with the nucleas of the matter which gives them vibrations and that vibration is turned into heat(for a resistor).
that is why i had this doubt whether electrical energy is in the kinetic energy of the electrons..

5. Jul 24, 2011

### gsal

Well, I am not going to say that I am 100% sure of what I have stated...I was just going for some kind of analogy, anyway.

Then again, imagine your house, at the electric company meter they measure how much current you are using...there are two wires, whatever current goes in one wire, comes out the other...they are equal...

does not matter how many paths there are in the house for the current to follow, whether they are "easy" paths or difficult ones (very resistive like an incandescent light bulb)...at every node where the current could split in two, the current is the same when those two paths get back together...

you see what I am going with this? It seems as if current is always flowing at the same speed no matter what the load is.

that is not to say that for a resistive element there are no collisions, you are correct in that respect...but it does not look like these collisions slow down the electrons that much...

or put another way, in order for the collision to not slow down electrons that much, you have to find a balance in how many electrons you want to send through and how much force (voltage) you use to push them....this is Ohm's Law: V=IR ....if you keep the voltage constant and up the resistance, then the amount of electrons going through go down...since there isn't enough push to handle the same amount of collisions....

does this help?

6. Jul 24, 2011

### elegysix

as for the velocity of current, look up drift speed... theres a formula: I=nAQv, where v is the electron drift speed.

Electrical energy is due to the electrical field, much like gravitational potential energy.

for a given electric field E, the energy density is given by

u=$\frac{\epsilon_{0}|E|^{2}}{2}$

hope this helps

7. Jul 24, 2011

### FireStorm000

I actually remember deriving this in my AP physics class. It really depends on what we're talking about though, because there are many different kinds of energy in an electric circuit. A capacitor stores energy in an electric field; an inductor stores energy in a magnetic field; batteries in chemical bonds. Resistors dissipate energy in the form of heat. In a perfect wire, there would be energy if the form of kinetic energy of the electrons, yes, but also in the magnetic field generated by the wire.

I know at least at the introductory college level, wires are not considered to store any energy(it's negligible). Electrons simply transfer the energy(supposedly instantaneously) from one component to the next.

8. Jul 26, 2011

### tushar gupta

thank u guys.. these answers really helped me.thanks again.

9. Aug 20, 2011

### Naty1

Gupta:
I am 99% sure that is not correct, but could not find a precise description within wiki...it is unlikely that nuclear activity is at the heart of heat generation...as the following excerpts indicate..... Since I was looking around I thought I'd post some interesting related explanations.

[My own GUESS is that as electrons get bumped around they gain energy from the electric potential (field), then give it off randomly as they move around...so they emit some low energy photons (radiation) and we observe this as heat. Loosly bound valence electrons would neither absorb nor susbequently emit much energy.....they move easily. If you look at the description below, I can visualize the "forbidden band" requiring more energy but then giving off more in return than just bumping an electron in the conduction band...]

I just checked my old physics text: it says the theory of resistance is quantum based, that classical reasoning of collisions and the like yield resistivites at least a hundred times too large. That classical reasoning involves electron collisions and the idea that free conduction electron motion is generally rapid, but that the imposed drift velocity imparts a slow uniform motion in the direction of the electric field.

http://en.wikipedia.org/wiki/Valence_electron#Valence_electrons_and_electrical_conductivity

http://en.wikipedia.org/wiki/Electrical_resistance

http://en.wikipedia.org/wiki/Resistance_heating#Resistance

Last edited: Aug 20, 2011