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%
From NCERT
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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%
From NCERT
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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 |
 50%
From NCERT
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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 |
From NCERT
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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 |
 59%
From NCERT
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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 |
 50%
From NCERT
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A body initially at 80°C cools to 64°C in 5 minutes and to 52°C in 10 minutes. The temperature of the body after 15 minutes will be 
(a) 42.7°C                  (b) 35 °C
(c) 47 °C                    (d) 40 °C

Subtopic:  Newton's Law of Cooling |
 56%
From NCERT
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Four identical rods of same material are joined end to end to form a square. If the temperature difference between the ends of a diagonal is 100°C, then the temperature difference between the ends of other diagonal will be -

(1) 0°C 

(2) 100l°C; where l is the length of each rod

(3) 1002l°C

(4) 100°C

Subtopic:  Conduction |
From NCERT
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A cylindrical rod with one end in a steam chamber and the other end in ice results in melting of 0.1 gm of ice per second. If the rod is replaced by another with half the length and double the radius of the first and if the thermal conductivity of material of second rod is 14 that of first, the rate at which ice melts in gm/sec will be -
(1) 3.2               

(2) 1.6

(3) 0.2               

(4) 0.1

Subtopic:  Conduction |
 74%
From NCERT
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