Question

  A brass telephone wire has essentially no sag between poles 35.0 m apart on a cold day when the temperature is -20.0°C. How much longer is the wire on a summer day when the temperature is 35.0°C? If we change the kind of wire copper, how much longer is it during summer? Which is longer?

Answer 1

$\Delta l_b=\alpha_b l_0\Delta t=3.6~cm,$

$\Delta l_c=\alpha_c l_0\Delta t=3.2~cm.$