# Help on magnetic field questionWatch

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#1
Hi I was doing this multiple choice question and I'm a bit confused how to work out the average magnetic force that acts on one electron? Or even all of the electrons I don't see how I'm supposed to use the area either, since the formula I'm thinking is F=Bil

Any help would be appreciated
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5 years ago
#2
(Original post by .raiden.)
Hi I was doing this multiple choice question and I'm a bit confused how to work out the average magnetic force that acts on one electron? Or even all of the electrons I don't see how I'm supposed to use the area either, since the formula I'm thinking is F=Bil

Any help would be appreciated
The question gives you the density of electrons (8x1028m-3), so you need to work out how many actual electrons (Ne) there are in the wire. Hence CSA and length are needed.

Then use F = Bil/Ne

If you write out the expanded equation, you could cancel the length term to leave F = Bi/rhoe*CSA

Spoiler:
Show
F = 0.2*8 / 8x1028*1x10-6

F = 2x10-23N

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