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Number of conduction electrons question

  • Thread starter raintrek
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1. Homework Statement

Calculate how many conduction electrons pass through a given area per second when a current of 1A flows.


2. Homework Equations

Current density, j = i/A (i=current, A=cross sectional area)
Current desntiy, j = nevD (n=no of electrons per unit volume, e=charge on electron, vD=drift velocity)

3. The Attempt at a Solution

I've taken an element of volume of length vDt and cross-sect area, A. I've surmised then that the total number of electrons in that area will be N=nAvDt.

All of those electrons will then cross a plane in 1 second, so i've equated j=i/A=nevD, and substituted n from the earlier (bold) equation - n=N/AvD. However, that produces a result of N=i/e=1/e ... doesn't look right! Help!!
 

Answers and Replies

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However, that produces a result of N=i/e=1/e ... doesn't look right! Help!!
That looks right to me. How do you think it should look like?
 
AlephZero
Science Advisor
Homework Helper
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Look at it a different way, forget about the current density etc.

1A = 1 coulomb/sec

If the charge on one electron is e coulombs, then one coulomb is the charge on 1/e electrons.
 
Last edited:

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