A solid cube and a solid sphere of the same material have equal surface area. Both are at the same temperature 120°C, then -

(1) Both the cube and the sphere cool down at the same rate

(2) The cube cools down faster than the sphere

(3) The sphere cools down faster than the cube

(4) Whichever is having more mass will cool down faster

Subtopic:  Stefan-Boltzmann Law |
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Two bodies \(A\) and \(B\) have thermal emissivities of \(0.01\) and \(0.81\) respectively. The outer surface areas of the two bodies are the same. The two bodies emit total radiant power at the same rate. The wavelength \(\lambda_B\) corresponding to maximum spectral radiancy in the radiation from \(B\) is shifted from the wavelength corresponding to maximum spectral radiancy in the radiation from \(A\), by \(1.00~\mu\text{m}\). If the temperature of \(A\) is \(5802~\text{K}\):

1. the temperature of \(B\) is \(1964~\text{K}\)
2. \(\lambda_B= 1.5~\mu\text{m}\)
3. the temperature of \(B\) is \(11604~\text{K}\)
4. the temperature of \(B\) is \(2901~\text{K}\)
Subtopic:  Wien's Displacement Law |
 56%
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A black body is at a temperature of 2880 K. The energy of radiation emitted by this object with wavelength between 499 nm and 500 nm is U1, between 999 nm and 1000nm is U2 and between 1499 nm and 1500 nm is U3. [Given : Wein's constant b=2.88×106 nm K}.  Then

(1) U1=0          

(2) U3=0

(3) U1>U2        

(4) U2>U1

Subtopic:  Wien's Displacement Law |
 64%
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A black metal foil is warmed by radiation from a small sphere at temperature T and at a distance d where surrounding temperature is To. It is found that the power received by the foil is P. If both the temperature and the distance are doubled, the power received by the foil will be - [Assume T>>To]
1. 16P                 

2.  4P

3. 2P                   

4. P

Subtopic:  Stefan-Boltzmann Law |
 57%
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Three rods of same dimensions are arranged as shown in figure they have thermal conductivities K1, K2 and K3 The points P and Q are maintained at different temperatures for the heat to flow at the same rate along PRQ and PQ then which of the following option is correct ?

 
(1) K3=12K1+K2

(2) K3=K1+K2

(3) K3=K1K2K1+K2

(4) K3=2K1+K2

Subtopic:  Conduction |
 71%
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Two metallic spheres S1 and S2 are made of the same material and have identical surface finish. The mass of S1 is three times that of S2. Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of the initial rate of cooling of S1 to that of S2 is 
(1) 1/3             

(2) 1/31/3

(3) 1/3          

(4) 3/1

Subtopic:  Stefan-Boltzmann Law |
 51%
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Three discs \(A,B\) and \(C\) having radii \(2~\text{m},4~\text{m},\) and \(6~\text{m}\) respectively are coated with carbon black on their surfaces. The wavelengths corresponding to maximum intensity are \(300~\text{nm},400~\text{nm},\) and \(500~\text{nm}\) respectively. The power radiated by them are \(Q_a,Q_b,\) and \(Q_c\) respectively, then:
1. \(Q_a\) is maximum
2. \(Q_b\) is maximum
3. \(Q_c\) is maximum
4. \(Q_a=Q_b=Q_c\)

Subtopic:  Wien's Displacement Law |
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The total energy radiated from a black body source is collected for one minute and is used to heat a quantity of water. The temperature of water is found to increase  from   20°C to 20.5°C . If the absolute temperature of the black body is doubled and the experiment is repeated with the same quantity of water at 20°C, the temperature of water will be 

1. 21°C               2. 22°C 
3. 24°C               4. 28°C 

Subtopic:  Stefan-Boltzmann Law |
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A solid sphere and a hollow sphere of the same material and size are heated to the same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surroundings is same , then

(1) The hollow sphere will cool at a faster rate for all values of T

(2) The solid sphere will cool at a faster rate for all values of T

(3) Both spheres will cool at the same rate for all values of T

(4) Both spheres will cool at the same rate only for small values of T

Subtopic:  Stefan-Boltzmann Law |
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A solid copper cube of edges 1 cm is suspended in an evacuated enclosure. Its temperature is found to fall from 100°C to 99°C in 100 s . Another solid copper cube of edges 2 cm, with similar surface nature, is suspended in a similar manner. The time required for this cube to cool from 100°C to 99°C will be approximately -
(a) 25 s                  (b) 50 s  
(c) 200 s                 (d) 400 s

Subtopic:  Stefan-Boltzmann Law |
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