- #1
hulkster1988
- 6
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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)
First Question 1. Homework Statement
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?
W= -qV
Plug in above, answer is (apparently) 10J
Second Question 1. Homework Statement
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?
W= PE stored in capacitor
W= -PE
= 1/2 QV
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
First Question 1. Homework Statement
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?
Homework Equations
W= -qV
The Attempt at a Solution
Plug in above, answer is (apparently) 10J
Second Question 1. Homework Statement
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?
Homework Equations
W= PE stored in capacitor
W= -PE
= 1/2 QV
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