Question

Give scientific reason for the following: (a) The telephone wires which sag in summer become straight in winter. (b) Why does an ordinary glass tumbler crack if very hot water is poured into it?​

Answer 1

Explanation:

a)During summer, the wires heat up and expand in length. Hence it sags down. During winter, the temperature drops and wires cool down. Due to decrease in temperature,it contracts in length and hence becomes straight.

b)When boiling water is poured into a thick tumbler its inner surface expands. However, due to low thermal conductivity of glass, the expansion of outer surface of the tumbler is quite small. Due to uneven expansion of the outer and inner surfaces, the tumbler breaks.