J"Calculating Work for Charging a Parallel Plate Capacitor

[xswtxoj]

Homework Statement

A parallel plate capacitor is changed to an electric potential of 334V by moving 3.78e16 electrons from one plate to the other. How much work is charging the capacitor?

Homework Equations

Delta V= Delta PE/ q
c=q/v

The Attempt at a Solution

Delta V= Delta PE/ q
rearrange to q * PE = 3.78E16 *334= 1.26E19

 

[LowlyPion]

What fraction of a coulomb is the 3.78*10¹⁶ electrons of charge?

 

[Delphi51]

I don't like the look of your "Delta V= Delta PE/ q" in this case. Due to the fact that the V changes as charge is added to the capacitor, you get a slightly more complicated formula for the energy of the charged capacitor: E = 0.5*Q*V. Roughly speaking, you use the average V so you get a factor of 0.5. Check it out at http://en.wikipedia.org/wiki/Capacitor

Delta V= Delta PE/ q
rearrange to q * PE = 3.78E16 *334= 1.26E19

Here you have rearranged incorrectly. Also, you have entered the charge in non-standard units. The charge is given as a certain number of electron charges, and this number must be multiplied by the charge in Coulombs on one electron.

 

[xswtxoj]

i think i should be the same where 1 j/c is = to 1 Ev, so ur saying the formula can't be done? (E=.5*q*v)