4. A pith ball is a small nonconducting ball covered with a uniform, conducting

Question

4. A pith ball is a small nonconducting ball covered with a uniform, conducting metal foil. Initially pith ball A is charged negatively, pith ball B is neutral, and they small distance d apart. Now, the balls are brought together, touch, and then separated so they are again distance d apart.

a) Which is true of the forces between the two pith balls?

1)Before they touch they repel, after they touch they attract, 2)Before they touch they attract, after they touch they have no effect on each other ,3)Before they touch they repel, after they touch they have no effect on each other, 4)Before they touch they have no effect on each other, after they touch they repel, 5)Before they touch they have no effect on each other, after they touch they have no effect on each other, 6)Before they touch they attract, after they touch they repel, 7)Before they touch they have no effect on each other, after they touch they attract, 8)Before they touch they attract, after they touch they attract, 9)Before they touch they repel, after they touch they repel

Explanation / Answer

before touch :

A has negative charge and B is neutral

since the distance d is small, due to electrostatic induction, nearer part of B will get positively charged and farther part of B will get negatively charged. Hence there will be net electrostatic attraction between them

after touch :

negative charge of A is equally shared by them. Now both are negatively charged.

Hence there will be net electrostatic repulsion between them

answer is 6

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