Two conducting spheres rest on insulating stands. Sphere B is smaller than Sphere A. Both spheres are initially uncharged and they are touching. A third conducting sphere, C, has a positive charge. It is brought close to (but not touching) Sphere B as shown. What is the net charge (positive, negative, or zero) on Sphere A?

Explanation:

Sphere B and sphere A are touching so they will act as a single body . A positively charged sphere C is brought near sphere B . So there will be induction of charge on sphere B and sphere A . Opposite charge will be induced on nearer sphere and same charge will be induced on distant sphere . Hence sphere B will be negatively charged and sphere A will be positively charged. The amount of charge induced on sphere B and A will be same and it will remain as long as sphere C is kept near sphere B . As soon as sphere C is removed , induced charges will also neutralize each other .

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