A table tennis ball covered with a conducting paint is suspended by a silk thread so that it hangs between tow metal plates. One plate is earthed, when the other plate is connected to a high voltage generator, what will happen to the ball.

Explanation

The table tennis ball when slightly displace, say toward the positive plate, gets attracted toward the positive plate due to induced negative charge on its near surface.
The ball touches the touches the positive plate and itself gets positively charged buy the process of conduction from the plate connected to high voltage genetated. On getting positively charged, it is repelled by the positive plate and , therefore, the ball touched the other plate (earthed), which has negative charge due to induction. On touchingh this plate, the positive charge of the ball gets neutralized and in turn the ball shares negative charge of hte earthed plate and is again repelled from this plate also, and this process is repeatd again and agian .
Here it should be understood that since the positive plate is connected to high voltage generator its potential and hence its charge will always remain same. As soon as this plate gives some of its charge flows from genetator to the plate, and an equal negative charge is always induced on the other plate.