An iron rod and a copper rod lie side by side. As the temperature is changed, the difference in lengths of the rods remains constant at a value of 40 cm. The ratio of original lengths of copper to iron is $\left({\mathrm{\alpha }}_{\mathrm{Cu}}=4.8\times {10}^{-5}{/}^0\mathrm{C},{\mathrm{\alpha }}_{\mathrm{Fe}}=1.2\times {10}^{-5}{/}^0\mathrm{C}\right)$