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12%20-%20Transference%20of%20Heat

12%20-%20Transference%20of%20Heat - 12 TRANSFERENCE OF HEAT...

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12 - TRANSFERENCE OF HEAT Page 1 ( Answers at the end of all questions ) 1 ) The figure shows a system of two concentric spheres of radii r 1 and r 2 and kept at temperatures T 1 and T 2 respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to ( a ) ln ( r 2 / r 1 ) ( b ) 2 1 1 2 r r r r - ( c ) r 2 - r 1 ( d ) 2 1 2 1 r r r r - [ AIEEE 2005 ] 2 ) If the temperature of the sun were to increase from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on the earth to what it was previously, will be ( a ) 4 ( b ) 16 ( c ) 32 ( d ) 64 [ AIEEE 2004 ] 3 ) The temperatures of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity K and 2K and thickness x and 4x, respectively are T 2 and T 1 ( T 2 > T 1 ). The rate of heat transfer through the slab, in a steady state, is f x ) T T ( A 1 2 × - with f equal to 4 ) According to Newton’s law of cooling, the rate of cooling of a body is proportional to ( ∆θ ) n , where ∆θ is the difference of the temperatures of the body and its surroundings and n is equal to ( a ) one ( b ) two ( c ) three ( d ) four [ AIEEE 2003 ] 5 ) The luminous intensity of a star is 8100 times that of the sun and its temperature is 4500 K. Assuming the surface temperature of the sun to be 6000 K, the ratio of radius of the star to that of the sun will be 6 ) Two rods ( one straight and other semicircular ) of the same material and same cross - sectional area are joined as shown in the figure. The points A and B are maintained at different temperatures. The ratio of the heat transferred through the semicircular rod to the heat transferred through the straight rod in a given time is [ AIEEE 2002] 7 ) A body with area A and temperature T and emissivity e = 0.6 is kept inside a spherical black body. What will be the maximum energy radiated ? ( a ) 0.60 σ AT 4 ( b ) 0.80 σ AT 4 ( c ) 1.00 σ AT 4 ( d ) 0.40 σ AT 4 [ IIT 2005 ] 8 ) In which of the following processes, heat loss is primarily NOT due to convection ?
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12 - TRANSFERENCE OF HEAT Page 2 ( Answers at the end of all questions )
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