Question

when aluminium leaves are positively charged and a rod having negative charge is brought NEAR it, then what happens ?

Answer 1

When aluminum leaves are positively charged and a negatively charged rod is brought near the electroscope three cases can be observed:

1. Magnitude of positive charge in the aluminum leaves is equal to the magnitude of negative charge in the rod: all the positive charges on the leaves will move to the cap of the electroscope near the negatively charged rod. Thus, the leaves will come to a no deflection position.
2. Magnitude of positive charge in the aluminum leaves is more than the magnitude of negative charge in the rod: some of the positive charges will move to the cap near the negatively charged rod, the deflection of the leaves will reduced but there will be some deflection due to positive charges on the leaves.
3. Magnitude of positive charge in the aluminum leaves is less than the magnitude of negative charge in the rod: all the positive charges on the leaves will move to the cap. Since, the high negative charge on the rod will again induce positive charge on the cap. As a result negative charges is observed on the leaves and the leaves will show deflection.