Tag: transfer of heat

Questions Related to transfer of heat

A sphere of density d, statisfied heat s and radius r is hung by thermally insulating thread in an enclosure which is kept at a lower temperature than the sphere.The temperature of the sphere to drop at a rate which depends upon the temperature difference between the and the enclosure,If the temperature difference is $ \triangle T $ and surrounding temperature is $ T _o $ then rate of fall in temperature will be-

physics transfer of heat applications of convection convection thermal energy transfers

  1. $ \frac {4 \sigma T _o^2 \triangle T}{rdc} $

  2. $ \frac {12 \sigma T _o^2 \triangle T}{rdc} $

  3. $ \frac {12 \sigma T _o^4 \triangle T}{rdc} $

  4. $ \frac {12\sigma \triangle T}{rdc T _o^3 } $

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Correct Option: A

The correct statement of the following:
A) Water can be boiled inside the artificial satellite by convection
B) Heavy liquid can be boiled in artificial satellite by convection
Mark correct option/s

physics transfer of heat applications of convection convection thermal energy transfers

  1. Both statements are correct

  2. Both statements are wrong

  3. A is correct but B is wrong

  4. B is correct but A is wrong

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Correct Option: B
Explanation:

Conduction and Convection are non-existent in space, so both the statements are wrong. 

It is hotter at some distance over the flames than in front of it because :

physics transfer of heat applications of convection convection thermal energy transfers

  1. air conducts heat upwards only

  2. heat is radiated upwards only

  3. convection of heat occurs upwards only

  4. heat is radiated downwards only

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Correct Option: C
Explanation:

Near flames, heat transfer occurs by both convection and radiation (and some conduction too).
But convection occurs only in upward direction. So, above the flame, it is hotter rather than in front of the flame.

Which of the following process(es) occur(s) during the convective transfer of heat within a large volume of air? 

physics transfer of heat applications of convection convection thermal energy transfers

  1. A continuous flow of warmer and cooler parts of air is established.

  2. The flow of air molecules results in flow of heat.

  3. The cooler portion of the air surrounding a warmer part exerts a buoyant force on it.

  4. As the warmer part of the air moves, it is replaced by cooler air that is subsequently warmed up.

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Correct Option: A,B,C,D
Explanation:

A continuous flow of warmer and cooler parts of air is established in which the air molecules are responsible for flow of heat. As the warmer air molecules move up, they are replaced bu cooler air molecules.

__and__are good conductors of heat

physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

  1. Silver, Copper

  2. Wood,Plastic

  3. Glass,Paper

  4. Pure water,Iron

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Correct Option: A
Explanation:
Silver and copper are good conductors of heat.
$\because$ Silver and copper are only metals present there and as we know metals have conductivity of heat and electricity than non-metal and metalloids. So, silver and copper are god conductors of heat.

State the correct statement

physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

  1. When we heat an object, it becomes hot

  2. When we heat an object, it expands in size

  3. When we heat an object, it changes its such such as water boils to form water vapour

  4. All of them are true

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Correct Option: D
Explanation:

When we heat an object, it changes its shape, nature and it becomes hot, the temperature increases due to movement of atoms.

Bad conductor of heat is

physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

  1. Copper

  2. Steel

  3. Silver

  4. None

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Correct Option: D
Explanation:

All of them, being metals, are good conductors.

The ............ the conductor, the more rapidly does heat transfer takes place.

physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

  1. better

  2. worse

  3. thinner

  4. thicker

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Correct Option: A
Explanation:

The better the conductor, the more rapidly does heat transfer takes place .


Better conductor means more thermal conductivity; more the thermal conductivity; more rapidly the heat transfer takes place.

The reason for providing copper bottoms in steel pans is :

physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

  1. aesthet, carly looks good

  2. that copper is better conductor than steel

  3. that copper is not a good conductor than steel

  4. None of the above 

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Correct Option: B
Explanation:

Copper bottoms are provided in steel pans because copper is better conductor of heat than steel.

Thermal conductivity of copper is highest ($38600w/mK$) while that of steel is lowest ($1245w/mK$).

Four rods of same material but with different radii and lengths are used to connect two reservoirs of heat with the same temperature difference. Which one will conduct more heat

physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

  1. r=1 cm, 1=1 cm

  2. r=1 cm, 1= 2 cm

  3. r= 1 cm, $1=\frac{1}{2}m$

  4. $r=\frac{1}{2}cm$, $1=\frac{1}{2}m$

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Correct Option: C