An ice box used for keeping eatable cold has a total wall area of 1 metre2 and a wall thickness of 5.0 cm. The thermal conductivity of the ice box is K = 0.01 joule/metre-s-°C. It is filled with ice at 0°C along with eatables on a day when the temperature is 30°C. The latent heat of fusion of ice is 334 ×103 joules/kg. The amount of ice melted in one day is ( 1 day = 86,400 seconds ) 
(a) 776 gms            (b) 7760 gms  
(c) 11520 gms         (d) 1552 gms

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Five rods of the same dimensions are arranged as shown in the figure. They have thermal conductivities K1, K2, K3, K4 and K5. When points A and B are maintained at different temperatures, no heat flows through the central rod if :

(a) K1=K4 and K2=K3
(b) K1K4=K2K3
(c) K1K2=K3K4
(d) K1K4=K2K3

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A hot metallic sphere of radius r radiates heat. It's rate of cooling is
(a) Independent of r              (b) Proportional to r
(c) Proportional to r2             (d) Proportional to 1/r

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Newton's law of cooling
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A solid copper sphere (density ρ and specific heat capacity c) of radius r at an initial temperature 200K is suspended inside a chamber whose walls are at almost 0K. The time required (in μs) for the temperature of the sphere to drop to 100 K is 
(a) 727rρcσ                  (b) 772rρcσ
(c) 277rρcσ                  (d) 727rρcσ

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Newton's law of cooling
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One end of a copper rod of uniform cross-section and of length 3.1 m is kept in contact with ice and the other end with water at 100°C. At what point along it's length should a temperature of 200°C be maintained so that in steady state, the mass of ice melting be equal to that of the steam produced in the same interval of time. Assume that the whole system is insulated from the surroundings. Latent heat of fusion of ice and vaporisation of water are 80 cal/gm and 540 cal/gm respectively .

(a) 40 cm from 100°C end                    (b) 40 cm from 0°C end
(c) 125 cm from 100°C end                   (d) 125 cm from 0°C end

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A sphere and a cube of same material and same volume are heated upto same temperature and allowed to cool in the same surroundings. The ratio of the amounts of radiations emitted will be
(a) 1 : 1                 (b) 4π3:1
(c) π61/3:1          (d) 124π323:1

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Stefan-Boltzmann law
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The temperature 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 T2 and T1 (T2 > T1). The rate of heat transfer through the slab, in a steady state is AT2-T1Kxf, with f which equals to -


(a) 1
(b) 12
(c) 23
(d) 13

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The figure shows a system of two concentric spheres of radii r1 and r2 and kept at temperatures T1 and T2, respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to -

(a) r1r2r1-r2
(b) r1-r2
(c) r1-r2r1r2
(d) In r2r1

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The graph shown in the adjacent diagram, represents the variation of temperature (T) of two bodies, x and y having same surface area, with time (t) due to the emission of radiation. Find the correct relation between the emissivity (e) and absorptivity (a) of the two bodies .

(a) ex>ey & ax<ay
(b) ex<ey & ax>ay
(c) ex>ey & ax>ay
(d) ex<ey & ax<ay

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The plots of intensity versus wavelength for three black bodies at temperatures T1T2 and T3 respectively are as shown. Their temperature are such that

(a) T1>T2>T3
(b)  T1>T3>T2
(c) T2 >T3 >T1
(d) T3>T2T1

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Wien displacement law
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