Question

Complete the following sentence : A rod is brought near the disc of a positively charged gold leaf electroscope. Ifthe divergence of leaves ........ , the rod is positively charged; if the divergence of leaves ........ the rod is negatively charged; if the divergence of leaves ....... , the rod is uncharged.

• A. decreases, decreases, decreases.
• B. increases, decreases, increases.
• C. increases, increases, decreases.
• D. increases, decreases, decreases.

Answer 1

The correct option is D increases, decreases, decreases.

When the negatively charged rod is touched on the disc of a positively charged gold leaf electroscope, the divergence between the gold leaves decreases as unlike charges attract each other.
When the positively charged rod is touched on the disc of a positively charged gold leaf electroscope, the divergence between the gold leaves increases as like charges repel each other.
When uncharged rod is touched on the disc of a positively charged gold leaf electroscope, the divergence between the gold leaves decreases as unlike charges attract each other. It is to be noted that a charged body can also attract an uncharged body, so repulsion is the sure test to determine whether the body is charged or not.
Therefore, when the uncharged rod is rolled on the disc of the positively charged gold leaf electroscope, the electrons from the electroscope are transferred to the rod and hence, the rod becomes negatively charged. Now the unlike charges attract each other and the divergence decreases.
Hence, A rod is brought near the disc of a positively charged gold leaf electroscope. If the divergence of leaves increases, the rod is positively charged; if the divergence of leaves decreases the rod is negatively charged; if the divergence of leaves decreases, the rod is uncharged.