# Maximum charge

1. Feb 14, 2012

### MrRandom66

1. The problem statement, all variables and given/known data
An empty, hollow, spherical conductor with radius R = 20 cm is supported in air. Electrical breakdown occurs when the electric field at the conducting surface exceeds 3.0 × 106 V m−1.
What is the maximum charge that can be placed on the sphere?

2. Relevant equations
F = k (q/r^2)
F = Eq

3. The attempt at a solution

Trying to rearrange these to find q, however all I can get is something which cancels out q.

2. Feb 14, 2012

### Staff: Mentor

I think there is something missing in the problem statement. The electric field has to be with respect to another conductor, placed some distance away (unless you can use infinity somehow). Is there anything else in the problem statement?

3. Feb 14, 2012

### MrRandom66

No, thats all.

4. Feb 14, 2012

### ehild

You certainly learnt that the electric field of a metal sphere is the same as if its whole charge concentrated in the centre.

Pretend that Q charge is in he centre of the sphere. What is the electric field at the surface of the sphere (R=20 cm)?

ehild

5. Feb 14, 2012

### ehild

Hi berkeman,

I think you meant electric potential, but it is electric field strength here.

ehild

6. Feb 20, 2012