There are these two homework questions that I think are asking the exact same thing, yet use different equations (and get different answers for them)(adsbygoogle = window.adsbygoogle || []).push({});

First Question 1. The problem statement, all variables and given/known data

A potential difference of 10V is present between the plates of a capacitor. How much work must be done to move 6.25x10^18 electrons from the negative plate to the positive plate?

2. Relevant equations

W= -qV

3. The attempt at a solution

Plug in above, answer is (apparently) 10J

Second Question 1. The problem statement, all variables and given/known data

4 uC of negative charge is transferred from one plate of a 8uF capacitor to the other plate. How much work was done by the electric field in this charging process?

2. Relevant equations

W= PE stored in capacitor

W= -PE

= 1/2 QV

3. The attempt at a solution

Plug it in, I get -1J

The thing is the above equation is for work stored in the capacitor, and the 1/2 is there because it is the average of V as it is charged from 0 to V.

So why does the first question use the formula for work that is for a charge, q, placed into a field? Shouldn't it to use the 1/2QV formula?

I'm definitely stumped on this one

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# Homework Help: Capacitor and Potential. EN - weird solution

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