Heat and Thermodynamics

Problems

1. Calculate the maximum net rate of loss of heat by radiation from a sphere of 10 cm radius at a temperature of 200 °C when the surroundings are at a temperature of 20 °C, if Stefan's constant is 5.7 × 10⁻⁵ ergs/sq cm/s/deg⁴.

   Ans. 3.659 × 10⁹ ergs/s

2. Calculate the radiation loss per sq cm per second from a black cylinder of emissivity 0.95 at 327°C when surrounded by an enclosure at 27 °C.

   Ans. 6579 × 10³ ergs

3. A hot black body of mass 64 gm, area 16 sq cm and specific heat 0.1 cal/gm/ °C is allowed to cool inside an evacuated enclosure surrounded by melting ice. It is found that at 300 °C, the body cools at the rate of 21 °C per minute; calculate Stefan's constant.

   Ans. 1.37 × 10⁻¹² cal/sq cm/s/deg⁴C

4. A solid copper sphere cools at the ...