Two chunks of metal with heat capacities C1 and C2 are interconnected by a rod of length l and cross-sectional area S and fairly low heat conductivity ×. The whole system is thermally insulated from the environment. At a moment t = 0 the temperature difference between the two chunks of metal equals (ΔT)0. Assuming the heat capacity of the rod to be negligible, find the temperature difference between the chunks as a function of time.