Question

When hot water is poured on a glass plate, it breaks because of :
(A) Unequal expansion of glass
(B) Equal expansion of glass
(C) Unequal contraction of glass
(D) Glass is delicate

Answer 1

Hint: Most substances on addition of heat have the tendency to expand. This is called thermal expansion. Glass also expands when its temperature is increased. This expansion is so sudden and unequal.

Complete step by step solution: Almost , all substances expand on addition of heat . When the temperature of glass is suddenly increased by addition of hot liquid , thermal expansion or contraction occurs rapidly near the inside surface of the glass . Glass being the poor conductor of heat , there is a time lag before expansion or contraction begins near the outside the surface .
When hot water is added , the atoms speed up and the glass expands. If the glass container is not brought up to much higher temperature in a uniform manner , the expansion will not be equally distributed over the surface .

This sudden tendency to expand puts strain on glass and stress is developed in the inner walls of glass which causes it to break .
Hence, it is the unequal expansion that causes the glass plate to break .

Hence, the correct option is A.

Note- All substances show thermal expansion and expand in accordance with their coefficient of thermal expansion.