Am I missing something? (stored energy U=.5QV)

[runran]

So there's this problem where they provide charge on each plate of .02E-9 Coulombs with a potential difference of 240 V. Parallel plates separated by .0004m air. Asks for energy stored in capacitator. I used U=.5QV equation to get 2.4E-6 J but didn't use the .0004 constant at all. Did I miss something in what calculation I'm supposed to be doing? Usually data isn't provided in a problem unless it's supposed to be used, but I can't think of how I would need that. Thank you.

 

[Hootenanny]

So there's this problem where they provide charge on each plate of .02E-9 Coulombs with a potential difference of 240 V. Parallel plates separated by .0004m air. Asks for energy stored in capacitator. I used U=.5QV equation to get 2.4E-6 J but didn't use the .0004 constant at all. Did I miss something in what calculation I'm supposed to be doing? Usually data isn't provided in a problem unless it's supposed to be used, but I can't think of how I would need that. Thank you.

Your logic is correct, however you calculations are not. The energy stored is by my calculations is 2.4 x 10^-9 J.

~H

 

[runran]

Woops, meant to put Q as .02E-6 c
But thanks Hootenanny for the reassurance that the solution is okay.

A cookie for you (::)

 

[Hootenanny]

A cookie for you (::)

Why thank you old chap

~H