Two rods having thermal conductivity in the ratio of 5 : 3 having equal lengths and equal cross-sectional area are joined by face to face. If the temperature of the free end of the first rod is 100°C and free end of the second rod is 20°C. Then temperature of the junction is

(1) 70 °C                   

(2) 50 °C

(3) 50 °C                  

(4) 90 °C

Subtopic:  Conduction |
 81%
From NCERT
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Woollen clothes are used in winter season because woollen clothes

(1) Are good sources for producing heat

(2) Absorb heat from surroundings

(3) Are bad conductors of heat

(4) Provide heat to body continuously

Subtopic:  Conduction |
 73%
From NCERT
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Two metal cubes and of same size are arranged as shown in the figure. The extreme ends of the combination are maintained at the indicated temperatures. The arrangement is thermally insulated. The coefficients of thermal conductivity of A and B are 300 W/m°C and 200 W/m°C, respectively. After steady state is reached, the temperature of the interface will be 

(1) 45°C
(2) 90°C
(3) 30°C
(4) 60°C

Subtopic:  Conduction |
 86%
From NCERT
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A cylindrical rod having temperature T1 and T2 at its ends. The rate of flow of heat is Q1 cal/sec. If all the linear dimensions are doubled keeping temperature constant then rate of flow of heat Q2 will be
(a) 4Q1           (b) 2Q1
(c)Q14            (d) Q12

Subtopic:  Conduction |
 73%
From NCERT
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A body of length 1m having cross sectional area 0.75 m2 has heat flow through it at the rate of 6000 Joule/sec. Then find the temperature difference if K = 200 Jm-1K-1 

(a) 20°C                     (b) 40°C
(c) 80°C                     (d) 100°C

Subtopic:  Conduction |
 89%
From NCERT
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A wall has two layers A and B made of different materials. The thickness of both the layers is the same. The thermal conductivity of A and B are KA and KB such that  KA = 3KB. The temperature across the wall is 20°C. In thermal equilibrium 

(1) The temperature difference across A = 15°C

(2) The temperature difference across A = 5°C

(3) The temperature difference across A is 10°C

(4) The rate of transfer of heat through A is more than that through B.

Subtopic:  Conduction |
 54%
From NCERT
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A metal rod of length 2m has cross sectional areas 2A and A as shown in figure. The ends are maintained at temperatures 100°C and 70°C. The temperature at middle point C is

1. 80°C

2. 85°C

3. 90°C

4. 95°C

Subtopic:  Conduction |
 82%
From NCERT
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Which of the following circular rods (given radius r and length l) each made of the same material as whose ends are maintained at the same temperature will conduct most heat ?

(1) r=2r0 ; l=2l0           

(2) r=2r0 ; l=l0

(3) r=r0 ; l=l0               

(4) r=r0 ; l=2l0

Subtopic:  Conduction |
 85%
From NCERT
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It is hotter for the same distance over the top of fire than it is inside of it, mainly because

(1) Air conducts heat upwards

(2) Heat is radiated upwards

(3) Convection takes more heat upwards

(4) Convection, conduction and radiation all contribute significantly transferring heat upwards

Subtopic:  Convection |
 59%
From NCERT
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One likes to sit in the sunshine in the winter season, because:

1. The air around the body is hot, and the body absorbs heat from it.
2. we get energy from the sun.
3. we get heat by conduction from the sun.
4. None of the above



 

Subtopic:  Conduction |
 63%
From NCERT
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