17.7 At 20 °C a steel ring has an inside diameter that is 0.5 mm smaller than the diameter of a steel rod, which is 0.2 m. The ring is heated until it fits over the rod, which remains at 20 °C. The tem- perature coefficient of linear expansion of steel is 12 × 10-6 K-1 What is the temperature of the ring when it is just large enough to fit over the rod?