A simple solar cooker consists of a blackened metal pot (assumed to behave as a…
PHYSICS · Subjective · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
A simple solar cooker consists of a blackened metal pot (assumed to behave as a perfect blackbody) of surface area 0.050m2 placed inside a transparent glass enclosure. Bright sunshine supplies a solar flux of 800Wm−2 normally on to the pot surface.
The enclosure traps a layer of air of thickness 2.0cm between the pot and the glass cover. During steady operation the temperature of the pot surface rises to 100∘C, while the temperature of the inner surface of the glass cover stabilises at 60∘C. Take the thermal conductivity of air as 0.026Wm−1K−1 and the Stefan–Boltzmann constant as 5.67×10−8Wm−2K−4.
(i) Calculate the rate at which radiant energy is absorbed by the pot from the Sun.
(ii) Calculate the rate of heat loss from the pot to the glass cover by conduction across the trapped air layer.
(iii) Explain why convection losses inside the enclosure are small.
(iv) Using your results, comment on which mode of heat transfer is dominant in raising the pot temperature in the solar cooker.