Question

An electroscope has a charged rod brought near it, but not touching, and the leaves open, Fig. I. Then a ground wire is attached to the electroscope and the leaves close, Fig. II. Finally, the ground wire and then the rod are removed. It is determined that the electroscope leaves have a net positive charge. Determine the charge of the rod and leaves in Fig. I :

• A. The rod has a net positive charge while the leaves have a net negative charge
• B. The rod has a net negative charge while the leaves have a net positive charge
• C. Both have a negative charge
• D. It is impossible to determine with the given information

Answer 1

Answer: (A)

The rod has a net positive charge while the leaves have a net negative charge

When in figure 2 the rod and ground wire are removed, positive charge remains on the leaves in figure 3.

Hence the negative charge on the electroscope must have drained through the ground wire. This means that the rod must have been positively charged, which attracted and gathered negative charges on the electroscope.