Question

An uncharged metal sphere hangs from a nylon thread. When a positively charged glass rod is brought close to the metalsphere, the sphere is drawntoward the rod. But if the sphere touches the rod, it suddenly flies away from the rod. Explain why the sphere is first attracted and then repelled.

Answer 1

When a charged rod is brought near a neutral metal sphere, the opposite charges are attracted towards the rod, causing an initial attraction. However, when the sphere touches the rod, the charges redistribute, leading to like charges repelling each other with a stronger force than the attraction between opposite charges, resulting in the sphere being repelled.

Step-by-step explanation:

When a charged rod is brought near a neutral substance, the distribution of charge in atoms and molecules is shifted slightly. Opposite charge is attracted nearer the external charged rod, while like charge is repelled. Since the electrostatic force decreases with distance, the repulsion of like charges is weaker than the attraction of unlike charges, and so there is a net attraction.

Thus, when a positively charged glass rod is brought close to the neutral metal sphere, the opposite charges in the metal sphere are attracted towards the rod. However, when the sphere touches the rod, it suddenly flies away from the rod. This is because the charges in the metal sphere redistribute, and now the like charges repel each other with a stronger force compared to the attraction between the opposite charges.

This repulsion causes the metal sphere to be repelled away from the rod, creating a net repulsive force.

Answer 2

Answer and Explanation:

According to the question, a metal sphere is hung by a nylon thread and this sphere is uncharged.

Now, in the first case, when positively charged rod is held closer to this sphere the charging of the sphere takes place by induction.

Positively charged rod near to the sphere induces negative charges on the surface of the sphere whereas the positive charges are repelled to the far surface of the sphere.

Now, when the distance between the rod and sphere reduces, force of attraction between both increases.

At the instant, when rod comes in contact with the sphere, charging of sphere takes [place by the method of conduction.

In conduction, same nature of charge is transferred to the object in contact, here positive charge from rod to sphere in same amount.

Since, both the rod and sphere are positively charged they repel.