Question

the telephone wires which sag in summer become straight in winter.

Answer 1

Answer:

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

Answer 2

Explanation:

Due to the thermal expansion of the wiring materials, the wires expand in both width and length. This affects electrical transmission lines, telephone lines, and telegraph lines because of the large space between supporting poles.

Example : Copper (Cu) Thermal Expansion= 17.6 μm/m/oC