1
AIPMT 2010 Prelims
+4
-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?
A
$${Q \over 4}$$
B
$${Q \over {16}}$$
C
2Q
D
$${Q \over 2}$$
2
AIPMT 2010 Prelims
+4
-1
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
A
$${{\sigma {r^2}{T^4}} \over {{R^2}}}$$
B
$${{\sigma {r^2}{T^4}} \over {4\pi {R^2}}}$$
C
$${{\sigma {r^2}{T^4}} \over {{R^4}}}$$
D
$${{4\pi \sigma {r^2}{T^4}} \over {{R^2}}}$$
3
AIPMT 2010 Prelims
+4
-1
Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature toC, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is
where $$\sigma$$ is the Stefan's constant.
A
$${{{r^2}\sigma {{\left( {t + 273} \right)}^4}} \over {4\pi {R^2}}}$$
B
$${{16{\pi ^2}{r^2}\sigma {t^4}} \over {{R^2}}}$$
C
$${{{r^2}\sigma {{\left( {t + 273} \right)}^4}} \over {{R^2}}}$$
D
$${{4\pi {r^2}\sigma {t^4}} \over {{R^2}}}$$
4
AIPMT 2009
+4
-1
A black body at 227oC radiates heat at the rate of 7 cals/cm2s. At a temperature of 727oC, the rate of heat radiated in the same units will be
A
50
B
112
C
80
D
60
EXAM MAP
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