A cylindrical rod of length l and cross-sectional radius r is placed at a distance of 50 r from a infrared point source S of power 1 . 25 kW as shown in the figure. The lateral surface of the rod is perfectly insulated from the surroundings. If the cross-section A absorbs 80 % of the incident energy and the temperature difference between the ends of the rod is constant, then the rate of heat flow through the rod in steady state is

Question

A cylindrical rod of length l and cross-sectional radius r is placed at a distance of 50 r from a infrared point source S of power 1 . 25 kW as shown in the figure. The lateral surface of the rod is perfectly insulated from the surroundings. If the cross-section A absorbs 80 % of the incident energy and the temperature difference between the ends of the rod is constant, then the rate of heat flow through the rod in steady state is, 0.2 J/s, 0.125 J/s, 0.1 J/s, 0.25 J/s

MARKS App · Accepted Answer

The rate at which energy is absorbed at A, P A = P s o u r c e 4 π 50 r 2 × π r 2 × 0 . 8 = 0.1 W Since the rod is in steady-state, energy absorbed per second at A flows through to B. So heat flow per sec is 0 . 1 J / s

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