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Question
A metal sphere is kept on an insulting stands. A negatively charged rod is brought near it, then the sphere is earthed as shown. On removing the earthing, and taking the negatively charged rod away, what will be the nature of charge on the sphere? Give reason for your answer.
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Solution 1
There will be positive charge on the sphere.
Reason :
Negatively charged rod will induce positive charge on the sphere and negative charge well move in ground from other end.
Solution 2
When we bring a negatively charged rod near the metal sphere, the free electrons in the sphere move away due to repulsion force and start piling up at the other end. The rear end becomes positively charged due to the deficit of electrons. After connecting the sphere to the ground, the electrons flow to the ground while the positive charges at the rear end remain as it is due to the attractive force of the negative charges on the rod. When the sphere is disconnected from the ground and the charged rod is removed, the positive charge spreads uniformly over the sphere as shown in the Figure below:
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