What is the capacitance of the two metal spheres

1. Feb 20, 2010

hover

1. The problem statement, all variables and given/known data
What is the capacitance of the two metal spheres shown in the figure ?

sphere one has 20nC of charge and the other has -20nC of charge. The change in voltage is 100V

2. Relevant equations
C=Q/(change in V)

3. The attempt at a solution
My question is how do yo determine what charge to put in for Q?

2. Feb 20, 2010

xcvxcvvc

Re: capacitance

It's given.

3. Feb 20, 2010

hover

Re: capacitance

but the thing is how would I know to use 20nC or -20nC? What if you had 2 charges that were something like -30nC and 20nC? How do you know what Q to choose?

4. Feb 20, 2010

xcvxcvvc

Re: capacitance

you will never be given a problem like that. the charge when dealing with capacitance will be symmetric if two values are given or it will be singular(where such an ambiguity is impossible)

5. Feb 20, 2010

hover

Re: capacitance

So i assume then that the answer here is just 2E-8/100 then

6. Feb 20, 2010

xcvxcvvc

Re: capacitance

assumed correct.

7. Feb 20, 2010

hover

Re: capacitance

Correct

thanks