PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
A laboratory uses an electrically heated, nearly black cylindrical cavity (emissivity ≈ 0.95) whose external surface area is 0.60 m². The laboratory air is maintained at 300 K. All heat losses occur by thermal radiation from the cavity’s outer surface; conduction and convection are negligible.
The cavity must be held at a uniform temperature of 1000 K for a materials test lasting several hours.
Answer the questions that follow.
(1) Determine the electrical power that must be supplied to the heating element to maintain the cavity at the required temperature under steady-state conditions.
(2) Engineers add a layer of high-performance insulation that reduces the effective radiating surface area by 20 % while leaving emissivity unchanged. Recalculate the electrical power required to keep the cavity at 1000 K in the modified configuration.
(3) Briefly explain, without additional computation, whether using a surface coating that lowers the emissivity of the cavity would increase or decrease the required electrical input power, and why.