This is - number of charges trough

[something_about]

This is urgent - number of charges trough...

hello



I can't figure out why the next formula tells us the number of charges that move trough cross-sectional area of the conductor.


If a segment of wire has N charges moving with average velocity v, then in time [delta]t the number of charges is

N * A * v * [delta]t


A is the cross-sectional area of the conductor
N is number of charged particles per unit volume

thank you

 

[Gokul43201]

The distance traveled by a charge in time $\delta t$ is, on average, [itex]v\delta t[/tex]. <br /> <br /> Construct a plane that cuts through the wire normally. We want to count the number of electrons passing through this plane in some time $\delta t$. Now, if all the electrons have velocity v, then for an electron to pass through the plane at some time t, it must have been no farther back than [itex]v\delta t[/tex] at a time $t-\delta t$. In other words, only those electrons contained within the cylinder (for a wire of circular cross-section) of length [itex]v\delta t[/tex] and area A, at a time $t-\delta t$ will be able to pass through the wall in the ensuing time [itex]\delta t[/tex]. This number is simply the product of the volume of this cylinder, [itex]Av\delta t[/tex] and the number density, N.[/itex][/itex][/itex][/itex][/itex]