A positively charged rod touches the top of an uncharged electroscope. Describe the leaves' movement when a negatively charged rod is brought near to the top of this electroscope.

• A. The leaves move closer together.
• B. The leaves move apart.
• C. The leaves stay the same.
• D. The leaves disappear.

Answer: (A)

When a charged conductor is near another charge, the charges inside rearrange without the objects touching. A negatively charged rod near the top of a positively charged electroscope causes induction: the region at the top facing the rod becomes more positive (electrons are pushed away from that area). This redistribution reduces the amount of like charge on the leaves. With less repulsion between the leaves, they move toward each other. The overall charge stays positive, since there’s no contact, but the leaves’ repulsion weakens due to the induction. That’s why the leaves come closer.