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.
What happens when two glass rods rubbed with wool are brought close to each other?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → They repel each other.
Option (1) They repel each other. — Correct. Both glass rods are rubbed with the same material, so both acquire the same kind of charge (positive), and like charges repel.
Option (2) They attract each other. — Incorrect. Attraction needs unlike charges, as between a glass rod rubbed with wool and a plastic rod rubbed with fur. Two glass rods rubbed alike carry the same charge.
Option (3) A chemical reaction occurs. — Incorrect. No new substance forms on rubbing, because only electrons move from one surface to the other. The charged rods then just exert an electric force on each other.
Option (4) No visible reaction occurs. — Incorrect. Both rods are charged, so a repulsive force acts between them and pushes a freely suspended rod away.
NCERT (2026-27):
Electric Charge – “It was observed that if two glass rods rubbed with wool or silk cloth are brought close to each other, they repel each other …”
Electric Charge – “… There are two kinds of electrification and we find that (i) like charges repel and (ii) unlike charges attract each other.”