If a positively charged glass-rod is used to charge an electroscope X by contact and an electroscope Y by induction, then

Analyze the question: A positively charged glass rod is used to charge two electroscopes in two different ways. Contact charging gives X one type of charge, and induction charging gives Y the opposite type.

Concept:

• Charging by contact: The charged body touches the electroscope, and the electroscope gets the same type of charge as the rod.
• Charging by induction: The charged body is brought near (without touching) the electroscope cap. The electroscope is briefly earthed, then the earth connection is removed, and then the rod is taken away. The electroscope ends up with the opposite charge to the rod.

Step-by-step solution:

1. Electroscope X (contact): • The positive rod touches the cap, and electrons flow from the electroscope to the rod. • X loses electrons, so X is positively charged.

2. Electroscope Y (induction): • The positive rod is brought near the cap, which attracts electrons to the cap. The leaf and stem become positive. • Earthing the electroscope lets electrons flow from the earth into it, neutralising the positive charge on the leaf. • The earth connection is removed first, and then the rod is taken away. The extra electrons are trapped and spread over the electroscope. • Y is negatively charged.

3. Conclusion: X is positive and Y is negative.

Why the other options fail:

• A and B suggest both get the same charge, which ignores the difference between the two methods.
• C reverses the two charges.
• E is wrong because induction does charge Y, provided it is earthed properly.

Exam tip: Remember "Contact = Same, Induction = Opposite". Also, in induction, always remove the earth connection before removing the charged rod.