AIPMT 2010 Prelims | Properties of Matter Question 64 | Physics

The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, whose outer surface radiates as a black body at a temperature TK is given by

$${{\sigma {r^2}{T^4}} \over {{R^2}}}$$

$${{\sigma {r^2}{T^4}} \over {4\pi {R^2}}}$$

$${{\sigma {r^2}{T^4}} \over {{R^4}}}$$

$${{4\pi \sigma {r^2}{T^4}} \over {{R^2}}}$$

AIPMT 2010 Prelims

MCQ (Single Correct Answer)

-1

A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod, when placed in thermal contact with the two reservoirs in time t?

$${Q \over 4}$$

$${Q \over {16}}$$

$${Q \over 2}$$

AIPMT 2009

MCQ (Single Correct Answer)

-1

The two ends of a rod of length L and a uniform cross-sectional area A are Kept at two temperatures T₁ and T₂ (T₁ > T₂). The rate of heat transfer, $${{dQ} \over {dt}}$$ through the rod in a steady state is given by :

$${{dQ} \over {dt}} = {{k\left( {{T_1} - {T_2}} \right)} \over {LA}}$$

$${{dQ} \over {dt}} = kLA({T_1} - {T_2})$$

$${{dQ} \over {dt}} = {{kA\left( {{T_1} - {T_2}} \right)} \over L}$$

$${{dQ} \over {dt}} = {{kL\left( {{T_1} - {T_2}} \right)} \over A}$$

AIPMT 2009

MCQ (Single Correct Answer)

-1

A black body at 227^oC radiates heat at the rate of 7 cals/cm²s. At a temperature of 727^oC, the rate of heat radiated in the same units will be

112

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