Thermodynamics, Statistical Physics, and Quantum Mechanics

8 PROBLEMS

and the density Take the outside

temperature to be a constant

4.9 Tea in Thermos (Moscow Phys-Tech)

One liter of tea at 90° C is poured into a vacuum-insulated container (ther-

mos). The surface area of the thermoswalls The volume

between the walls is pumped down to atm pressure (at room

temperature). The emissivity of the walls and the thermal capacity

of water Disregarding the heat leakage through the

stopper, estimate the

a) Net powertransfer

b) Time for the tea to cool from 90°C to 70°C.

4.10 Heat Loss (Moscow Phys-Tech)

An immersion heater of power W is used to heat water in a
bowl.After 2 minutes, the temperature increases from to
90°C. The heater is then switched off for an additional minute, and the
temperature drops by Estimate the mass of the water in the
bowl. Thethermal capacity of water c= 4.2•