# Creating a charged object

1. Jun 3, 2009

### Frogmansailor

I am doing some conceptual design, and was hoping to be able to get some answers here before I devote too much time to this.

I would like to be able to charge a piece of aluminum so that it holds a charge (negative) of 8 Coulombs. I was hoping to achieve this with something similar to a van der graaf generator, which would charge a spherical piece of aluminum which is encased in a strong insulator so that the charge is safely contained.

So my questions are:

How big would this piece of aluminum have to be?
Would a van der graaf type generator work for this application?
How fast would this conductor bleed it's charge?
What insulator would best reduce this loss of charge?

Dave

2. Jun 3, 2009

### Manchot

It's not gonna happen. The field at the surface of a sphere is Q/(4*pi*epsilon_0*R^2), and air breaks down at a field strength of about 1 MV/m. To put 8 Coulombs on the sphere, you'd then need a sphere of a radius of 268 m to prevent the air around it from breaking down. 8 Coulombs is a lot of charge.

3. Jun 4, 2009

### Frogmansailor

Well the dielectric breakdown of air being so low is the reason I want to surround it with a better insulator, so that isn't accurate.

I realize 8 C is a ton of charge, I was just hopeful I guess. What would the maximum charge that one could put on a sphere about the size of a basketball then?