Question

A copper wire has essentially no sag between poles 50 m apart on a winter day when temperature is at 10° C.How much longer is the copper wire on a summer day when T=35.0°C?

Answer 1

$$\Delta l=\alpha \Delta Tl\\\Delta l=(16.7\cdot10^{-6})(35-10)(50)=0.0209\ m$$