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%
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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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Air is a bad conductor of heat or partly conducts heat. Still, a vacuum is to be placed between the walls of the thermos flask because:

1.  it is difficult to fill the air between the walls of the thermos flask.
2. due to more pressure of air, the thermos can get cracks.
3. by convection, heat can flow through the air.
4. on filling the air, there is no advantage.
Subtopic:  Convection |
 79%
From NCERT
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While measuring the thermal conductivity of a liquid, we keep the upper part hot and the lower part cool, so that:

1. convection may be stopped.
2. radiation may be stopped.
3. heat conduction is easier downwards.
4. it is easier and more convenient to do so.


 

Subtopic:  Convection |
 61%
From NCERT
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Mode of transmission of heat, in which heat is carried by the moving particles, is 
(1) Radiation           

(2) Conduction

(3) Convection         

(4) Wave motion

Subtopic:  Convection |
 69%
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In heat transfer, which method is based on gravitation ?

(1) Natural convection               

(2) Conduction

(3) Radiation                             

(4) Stirring of liquids

Subtopic:  Convection |
 78%
From NCERT
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When fluids are heated from the bottom, convection currents are produced because -

(1) Molecular motion of fluid becomes aligned

(2) Molecular collisions take place within the fluid

(3) Heated fluid becomes more dense than the cold fluid above it

(4) Heated fluid becomes less dense than the cold fluid above it

Subtopic:  Convection |
 69%
From NCERT
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If a liquid is heated in weightlessness, the heat is transmitted through 

(1) Conduction

(2) Convection

(3) Radiation

(4) Neither, because the liquid cannot be heated in weightlessness

Subtopic:  Conduction |
From NCERT
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