Question

hi all, please i would like to know how the electric energy is transferred in a circuit despite the slow movement of the electrons? even in AC circuit the electrons do not move? I'm asking this question because we say for example when a charge DQ passes through the whole resistor it will lose it potential equal to iR but my question is how this charge DQ will pass through the whole resistor even with it low speed? thank you

Answer 1

the charges may have low speed.. but current not only depends on how FAST the charges move.. also depends on HOW MUCH charges move

i = dq/dt...

so i is high.. if speed is high or the number of charges are high... it turns out.. that these materials have a very high number of electrons in them.. and thus you can have high values of current, even though the speed is low!

Answer 2

yes i know there's a large of number inside the resistor but the value of U=R*I is the potential drop between the two terminals of the resistor for 1 coulomb of charge but actually no charges have passed through the whole resistor i mean that they didnt pass through the whole length of the resistor and lost U=R*I of potential.

Answer 3

because in all books they say that the potential difference between two terminals is the loss of electric energy per 1 coulomb that passes through the whole resistor but actually inside the resistor there's a lot of charges and all of them didnt pass the whole resistor
so what is the dependency between them.. thank you

Answer 4

im talking about the electric energy and not the value of the current

Answer 5

well electric energy is no current alone, not voltage alone it is combination of both that is power and it flows through the wire or any transmission line, so basically when electric field is applied , electrons get drifted in the direction of applied electric field. now another case is just think of vibrating string similarly even if electron vibrates at its place it releases energy (you can refer piezoelectric material and generation of electricity in it) .but i dont think concept of stationary charge is right, because free electron does move in wire therefore there is concept of drift velocity, electron diffusion and a lot more...and its the movement of charge that releases energy and your power is transferred. and its not necessary that whole electron should pass through resistor, may be some will collide to another electron and will be stationary but some of them will be drifted with applied electric field and this is how electric power is transferred

Answer 6

hi ghazi here's a quote from a book called fundamentals of physics by Walker and Halliday : "Because there is an external conducting path between the two terminals of the battery, and because the potential differences set up by the battery are main- tained, a steady current i is produced in the circuit, directed from terminal a to terminal b. The amount of charge dq that moves between those terminals in time in- terval dt is equal to i dt. This charge dq moves through a decrease in potential of magnitude V, and thus its electric potential energy decreases in magnitUde by the amount dU=dq*dV..."

im talking about those charges. how those charges will cross the whole resistor (from terminal to another terminal) with its low velocity? and here they are talking that dq=i*dt or i is by area section so how we are talking about dq passing through the whole resistor?

Answer 7

Actually, the charges (electrons in most cases) are moving at the speed of light, but they don't take a direct path from one end of the conductor to the other. They behave like a bunch of billiard balls only they have charge so it's more like "springy" billiard balls. They, basically bounce around, banging into each other. So, the net movement through the conductor appears slow.

It's like how the wrinkles in a coastline makes it much longer than the line-of-sight distance between two points. The distance that a whale might swim between Los Angeles and San Diego (California), is much shorter than the distance a horse might travel, if the horse follows the contours of the coastline, whereas the whale follows the general shape of the coast.

Also, they transfer energy for one to another, so it's more the energy that moves through the conductor than the actual charge carriers. It's like how a wave moves along the surface of water. The water molecules mostly just bob up and down -- they don't move much in the direction of the wave motion. It's the energy transfer between the molecules that move the wave.

I'm sure there is a more sophisticated answer to this question, but hopefully this gives you the idea.

Answer 8

But just what i'm not understanding is when we say that an amount of charge dq passes through the whole length of the resistor between a time dt is equal to dq=I(intensity)*dt but as we know I(intensity) is for a sectional cross area of the resistor so how we say that this amount of charge passed through all the length of the resistor?
Thank you

Answer 9

Note that the charge movement is not dq(in) itself passing through the resistor
Under the influence of the potential difference V dq(in) is pushed into the resistor and dq(out)is pushed out "simultaneously" (limited by the speed of light of course) like a railroad train traveling through a tunnel with the flow of cars given in cars/sec entering the tunnel [dq(in)/dt] which equals [dq(out)} assuming no cars are squashed in the tunnel.