A composite metal bar of uniform section is made up of  equal lengths of copper,  nickel and  aluminium. Each part being in perfect thermal contact with the adjoining part. The copper end of the composite rod is maintained at 100°C and the aluminium end at 0°C. The whole rod is covered with belt so that there is no heat loss occurs at the sides. If KCu=2KAl and KAl=3KNi , then what will be the temperatures of Cu-Ni and Ni-Al junctions respectively ?

(a) 23.33°C and 78.8°C        (b) 88.89 °C and 22.22 °C
(c) 50°C and 30°C                (d) 30°C and 50°C

Subtopic:  Conduction |
 75%
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Three rods of identical area of cross-section and made from the same metal form the sides of an isosceles triangle ABC, which is right-angled at B. The points A and B are maintained at temperatures T and 2T respectively. In the steady state, the temperature of point C is TC. Assuming that only heat conduction takes place, TCT is equal to:
1. 12+1
2. 32+1
3. 122-1                  
4. 132-1

Subtopic:  Conduction |
 52%
From NCERT
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The only possibility of heat flow in a thermos flask is through its cork which is 75 cm2 in area and 5 cm thick. Its thermal conductivity is 0.0075 cal/cmsec°C. The outside temperature is 40°C and latent heat of ice is 80 cal g-1. Time taken by 500 g of ice at 0°C in the flask to melt into water at 0°C is -

(a) 2.47 hr
(b) 4.27 hr
(c) 7.42 hr
(d) 4.72 hr

Subtopic:  Conduction |
 64%
From NCERT
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A sphere, a cube and a thin circular plate, all made of the same material and having the same mass are initially heated to a temperature of 1000°C. Which one of these will cool first ?
(1) Plate                     

(2) Sphere

(3) Cube                     

(4) None of these

Subtopic:  Stefan-Boltzmann Law |
 59%
From NCERT
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Two identical conducting rods are first connected independently to two vessels, one containing water at 100°C and the other containing ice at 0°C. In the second case, the rods are joined end to end and connected to the same vessels. Let q1 and q2 g / s be the rate of melting of ice in two cases respectively. The ratio of q1/q2 is

(a) 12                 (b) 21
(c) 41                 (d) 14

Subtopic:  Conduction |
From NCERT
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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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