# Maximum negative voltage of a sphere?

I would like to know the maximum voltage that a metal sphere can hold from applying negative charge to it.

My thoughts are that the maximum voltage is the breakdown voltage of the surrounding medium (air in this case). I assume that at that voltage, electrons would arc from the sphere to the nearest object. I found that air actually has a breakdown electric field strength of 3 MV/m, which I assume to mean that if there is an object one meter away from a sphere charged to 3 MV, breakdown will occur (likewise, if there is an object three meters away, I can go up to 9 MV before breakdown occurs, etc.).

Since the work required to apply another charge increases with each charge applied, I imagine that perhaps special equipment would be required to actually achieve such a large voltage. What equipment is capable of this?

I would also like to know the best practical (household or within a reasonable purchase) way of applying a specific amount of negative charge to a metal sphere. I imagine that I could charge a capacitor and discharge half of the voltage into the sphere since the system would achieve equilibrium once the voltage of the capacitor matches the voltage of the sphere. I imagine a coulombmeter would otherwise be of great service.

Last edited:

davenn
Gold Member
Since the work required to apply another charge increases with each charge applied, I imagine that perhaps special equipment would be required to actually achieve such a large voltage. What equipment is capable of this

are you familiar with Van De Graff generators ?

you have given no indication of what electronics/electrical experience you have
you can be dealing with VERY high voltages, in this sort of experimenting, that can kill
Be very careful

Cheers
Dave

G Cooke
are you familiar with Van De Graff generators ?
Oh yes, I forgot about Van de Graaff generators. We used one for demonstration in Physics II.
you have given no indication of what electronics/electrical experience you have
you can be dealing with VERY high voltages, in this sort of experimenting, that can kill
Be very careful
Thanks for the warning. I'm not as concerned with high voltage as I am with being able to apply a specific, chosen voltage. I just wanted to know the maximum so that I would know how easy it would be to accomplish my experiment. So far, I think the best way to do this would be to charge a capacitor and discharge half of its voltage into the sphere, but I'm interested in what you and others think.

It is important that the voltage be negative, so I assume by simply touching the negative side of the capacitor to the sphere, I can achieve this.

Last edited: