Finding the potential difference?

[Simon316]

okey the question goes like this

A plate capacitor with area A and distance d1 is charged to a potential difference of V1 between the plates. Now the distance between the plates increases to d2 = 2*d1.

a) What is the new potential difference, V2, between the plates?

b) Find the increase in stored energy, deltaU, an explain where this energy comes frome.

what I have found out so far is:
a) V2 = E*2*d1, where E = Q/(e0*A) and therefore does not change with distance.

b) deltaU = 1/2*Q*V2 - 1/2*Q*V1


I don't think these two answers are good enough, but I can't se what else to do, maybe use intgral?
any help is highly appreciated

Kind regards

Simon

 

[denverdoc]

Simon,

using your eqn a) what is the ratio v2/v1?

 

[Simon316]

well the ratio must be V2/V1 = d1, but this can't be the answer to a) could it?

 

[denverdoc]

unless I miss my guess, it should be 2di/di=2.

 

[Simon316]

hehe yea ofcorse
but I still don't think the ration is the answer to thequstion, thanks though