Question

Explain thermal expansion with suitable examples.

Answer 1

1. Thermal expansion:
   The expansion of a substance on heating is called, the thermal expansion of that substance.
2. Fitting the iron rim on the wooden wheel:
   a. The diameter of the iron ring is slightly less than that of the wooden wheel.
   b. So, it cannot be easily slipped on from the rim of a wooden wheel.
   c. The iron ring is, therefore, first heated to a higher temperature so that it expands in size and the hot ring is then easily slipped over to the rim of the wooden wheel.
   d. Coldwater is now poured on the iron ring so that it contracts in size and holds the wooden wheel tightly.

3. Rivetting:
   a. Rivets are used to join two steel plates together.
   b. Hot rivet is driven through the hole in the plates.
   c. One end of the rivet is hammered to form a new rivet head.
   d. When cooled, the rivet will contract and hold the two plates tightly together.

4. Cracking of a thick glass tumbler:
   a. Glass is a poor conductor of heat.
   b. When hot liquid is poured into the tumbler, the inner surface of the tumbler becomes hot and expands while the outer surface remains at room temperature and does not expand.
   c. Due to this unequal expansion, the tumbler cracks.