PAL 3/12/12

1. PAL 3/12/12 • Each of the following can be a clue to what type process is occurring in a particular situation. Identify what type of process each of the following is a clue to. Remember: clue is not proof! • heat bath, heat sink, or heat reservoir • open to the atmosphere • rigid container • very quickly • piston-cylinder system • insulated

2. A glowing filament at 5000oC is held inside an evacuated glass container. The temperature at the outside surface of the glass is 100oC, the temperature at the inside surface of the glass is unknown, T. The container is a 30-cm cube, and the glass is 5 mm thick. The area of the filament in 10 mm2; its emissivity is 0.95. The thermal conductivity of the glass is 1.05 W/(mK). • Write down an expression for the rate at which heat is transferred from the filament to the inside of the glass. • Write down an expression for the rate at which heat is transferred from the inside of the glass to the outside. • When the inside surface of the glass has reached a constant temperature, what is true about these two heats? Write down that expression. • Can you justify that one term is small and can be neglected? If so, justify it, and then neglect it. • Solve for the temperature, T. (Double-check that any terms you neglected were actually negligible.)