Question

Electric wires sag in summer and become taut in the winter. Reason?
(A) They perform simple harmonic oscillations according to changes in the seasons.
(B) They expand due to summer heat and contract due to winter cold
(C) They expand due to winter cold and contract due to summer heat
(D) There is no specific reason

Answer 1

Hint:The electric wires are used to carry the current from the power station to the different localities. Sometimes these cables appear as sagged or remain tight, this is due to the changes in the temperature in the environment surrounding the cables.

Complete step by step answer:
The materials when exposed to heat, the molecules in the materials vibrate much causing one another to hit due to heat. This causes them to move wider apart. This process is called thermal expansion. The same process happens in the electric wire.


During summer, the heat makes the molecules move wider apart and hence it sags and during the winter follows the opposite process and gets contacted. While designing the cables, these must be considered. The other examples of the thermal expansions are bridges constructed along the rivers, railway lines, lid of the glass jar etc.

Thus the option (B) is correct.

Note:If the cables are laid in winter in a loose way, it gets more sag at the time of summer. If the cables are laid tightly in the summer, then it cannot contract in winter causing it to snap. Hence the selection of the material and the season must be considered while designing.