Case: Read the passage and answer the following questions.
Historically the credit for the discovery of the fact that amber rubbed with wool or silk cloth attracts light objects goes to Thales of Miletus, Greece, around 600 BC. The name electricity is coined from the Greek word ‘electron’ meaning amber. Many such pairs of materials were known which on rubbing could attract light objects like straw, pith balls and bits of paper. For example, cut out long thin strips of white paper and lightly iron them. Take them near a TV screen or computer monitor. We can see that the strips get attracted to the screen. In fact, they remain stuck to the screen for a while.
A glass rod is rubbed with a silk cloth. Both of them can now attract small bits of paper. The rod is then brought in contact with the same silk cloth and taken away. What is observed now?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → The rod and the silk no longer attract each other or the bits of paper.
Rubbing gives the rod and the silk unlike charges. When the two are brought back in contact, the charges they gained on rubbing are lost.
Option (1) The rod and the silk no longer attract each other or the bits of paper. — Correct. After contact, the charges gained on rubbing are lost. Both bodies become neutral, so they show no attraction at all.
Option (2) The rod and the silk now repel each other. — Incorrect. Repulsion needs like charges on the two bodies. Here both bodies lose their charge.
Option (3) The rod still attracts bits of paper, but the silk does not. — Incorrect. The rod and the silk had equal and opposite charges. Contact removes the charge from both of them.
Option (4) The rod and the silk attract each other more strongly than before. — Incorrect. Contact does not add charge. It removes the charges, so the attraction disappears.
NCERT (2026-27):
Electric Charge – “Now if the electrified glass rod is brought in contact with silk, with which it was rubbed, they no longer attract each other. They also do not attract or repel other light objects as they did on being electrified.”
Electric Charge – “Thus, the charges acquired after rubbing are lost when the charged bodies are brought in contact.”