# Question about Van De Graaf generator

1. Oct 2, 2012

1. The problem statement, all variables and given/known data
I have a sentence in my textbook that reads:

Because the "breakdown" electric field in air is about 3 X 106 V/m, a sphere 1.00m in radius can be raised to a maximum potential of 3 X 106 V

And now the problem states: The metallic sphere on top of a large van de Graaf generator has a radius of 2.0 m. Suppose that the sphere carries a charge of 3x10-5 C

2. Relevant equations
V = Q/4∏rε0

3. The attempt at a solution
Does that mean to find the Volt, I have to simply multiply that 3 X 106 V by 2, to give me 6 X 106 V?

Or do I have to use the above equation to find the volt inside the generator?

2. Oct 2, 2012

### Staff: Mentor

Why not employ your Relevant Equation?

3. Oct 2, 2012

I guess it's the line from the text that confused me as to whether that equation was even necessary or not

4. Oct 2, 2012

### Staff: Mentor

The line in the text is telling you what limits the maximum potential on a surface (before breakdown and arcing occur to drain off the charge). If your calculated potential approaches this value, stand well back from the apparatus!!!