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A and B are two points on a uniform metal ring whose centre is C. The angle ACB = θ. A and B are maintained at two different constant temperatures. When θ = 180°, the rate of total heat flow from A to B is 1.2 W. When θ = 90°, this rate will be (a) 0.6 W (b) 0.9 W (c) 1.6 W (d) 1.8 W |
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Answer» Correct Answer is: (c) 1.6 W Let R = total thermal resistance of the ring, ΔT = difference in temperature between A and B. For θ = 180°, two sections of resistance R/2 each are in parallel. Equivalent resistance = R/4. Rate of total heat flow = I1 = 1.2 = ΔT/R/4 or 0.3 = ΔT/R For θ = 90°, two sections of resistances R/4 and 3R/4 are in parallel. Equivalent resistance = (R/4)(3R/4) / R/4 = 3R/4 = 3R/16 . Rate of total heat flow I2 = ΔT/3R/16 W = 16/3 (ΔT/R) W = 16/3 x 0.3 W = 1.6 W. |
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