A positively charged glass rod is placed near the cap of a positively charged electroscope. The divergence of the leaf is observed to

Analyze the question A gold-leaf electroscope is already positively charged, so its leaf and cap/plate carry positive charge and the leaf diverges. A positively charged rod is brought near the cap (without touching). We need to find what happens to the divergence.

Concept: Charging by induction When a charged body is brought near the cap, the free electrons in the metal move.

• A positive rod attracts electrons toward the cap (the end closest to the rod).
• This leaves the leaf and stem with a deficiency of electrons, so they become more positively charged.

Step-by-step solution

1. The electroscope is already positive, so the leaf is diverged.
2. A positive rod brought near the cap pulls electrons up to the cap.
3. The leaf and stem lose electrons, so they become more positive.
4. More positive charge on the leaf and stem gives greater repulsion between them, so the leaf diverges more.

The total charge on the electroscope stays the same. Only the distribution changes, with more positive charge pushed down to the leaf.

Answer: The divergence increases, which is option B.

Option A (decrease) would happen if a negative rod were brought near. Option D is wrong because the leaf would only collapse if the charge were neutralized, which a positive rod cannot do here.

Exam tip: Remember the rule for a charged electroscope.

• Like charge brought near: divergence increases.
• Opposite charge brought near: divergence decreases (and may collapse, then re-diverge if the rod's charge is strong enough).

Only a charged object of the opposite sign reduces the divergence, so check the signs first.