# physics

A copper telephone wire has essentially no
sag between poles 30 m apart on a winter day
when the temperature is −16◦C.
How much longer is the wire on a summer
day when the temperature is 26 ◦C? Assume
that the thermal coefficient of copper
is constant throughout this range at its room
temperature value of 1.7 × 10−5 (◦C)−1.

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1. Increase = (26-(-16))C*1.7*10^-5/C*30cm
= 42*1.7*10^-5 * 30cm =0.02142 cm.

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