Two identical, solid metal spheres are initially at different temperatures. Sphere A is at 400K and Sphere B is at 300K. The spheres are placed gently in thermal contact inside a well-insulated enclosure so that no energy enters or leaves the combined system.
Answer the following parts about the subsequent thermal interaction between the two spheres.
(1) Part 1: (a) On a set of labeled axes with temperature on the vertical axis and time on the horizontal axis, sketch qualitatively plausible curves for the temperature of each sphere from the moment of contact until thermal equilibrium is reached. Clearly label which curve corresponds to each sphere and indicate the final equilibrium temperature on the graph.
(2) Part 2: (b) Describe, in words, the direction of net energy transfer between the spheres during the approach to equilibrium. In your explanation, include a microscopic interpretation based on atomic collisions.
(3) Part 3: (c) Explain how you can determine from the graph the instant at which the spheres reach thermal equilibrium, and state what physical condition is satisfied at that instant.