# Physics concept question

1. Feb 12, 2005

### Coldie

A negatively charged rod is brought near a suspended metal sphere. The sphere is 'grounded' by touching it with a finger. The finger and the rod are now removed. What charge will be on the sphere, positive or negative? Explain what happens.

Initially I thought that the finger would remove any induced charge that the sphere took on from the rod, but now I'm questioning that position. Can someone explain to me whether I'm wrong, and if so, how things really work?

Thanks.

2. Feb 12, 2005

### Gokul43201

Staff Emeritus
When you bring the rod close to the sphere, you induce negative charges on the far side of the sphere and positive charges on the near side. Basically, the electrons on the sphere want to be as far away from the rod as possible. By grounding the sphere you provide a path for these electrons (negative charges) to leave the sphere and this is exactly what they wanted. So the negative charges leave the sphere, making it ....

3. Feb 12, 2005

### Coldie

I see. So if the rod and the finger were both on the same side and then removed, then the change in charge of the sphere would ideally be zero?

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