Question

The telephone wire which sag in summer become straight in winter

Answer 1

Because the cores of overhead wires are made from copper. Metals expand with heat and contract with cold. The higher temperatures in summer make the copper expand - so the lines get slightly longer. In winter, the reverse happens - the lines contract and tighten up.

Answer 2

this due to the effect of temprature on heating an object contracts while on freezing it expands .

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