Tag: transfer of heat

Questions Related to transfer of heat

The walls of thermo-flask are polished because

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. shining bodies are good absorber of heat

  2. shining bodies are good radiator of heat

  3. shining bodies have emisivity as one

  4. none of the above

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Correct Option: B
Explanation:

The wall of thermoflask are polished because shiny surface are good radiators of heat. Since we intend to keep in the vacuum flask and not have it radiated, Outside the shiny surface is best option. A black wall is bad option as they are good emitter and absorber of heat radiation.

The vacuum between the walls of the flask prevents the transfer of heat by

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. Conduction

  2. Convection

  3. Radiation

  4. All

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Correct Option: A
Explanation:

Thermos flask is a special kind of bottle used for keeping the hot liquid hot and the cold liquid cool for a sufficiently long time. It was deviced by sir James Dewar and do it is also known as Dewar Flask. The vacuum between the walls of the flask prevents the transfer of  heat by conduction.

Thermos flask was deviced by

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. Fischer

  2. Joseph Lister

  3. Joseph Fourier

  4. Sir James Dewar

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Correct Option: D
Explanation:

Thermos flask is a special kind of bottle used for keeping the hot liquid hot and the cold liquid cool for a sufficiently long time. It was devised by sir James Dewar and do it is also known as Dewar Flask.

Thermos flask is a special kind of 

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. Bottle

  2. Process

  3. Apparatus

  4. Weighing machine

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Correct Option: A
Explanation:

Thermos flask is a special kind of bottle used for keeping the hot liquid hot and the cold liquid cool for a sufficiently long time.

A polished silver surface is

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. good absorber of heat

  2. good reflector of heat

  3. poor reflector of heat

  4. none of these

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Correct Option: B
Explanation:

Heat rays are electromagnetic rays. Light rays are also electromagnetic rays. We know that a polished silver surface is a good reflector of light. this means that it is a good reflector of electromagnetic rays. Hence it is a good reflector of heat

A thermos flask maintains temperature of objects. It

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. containing some kind of heating element to keep hot things hot.

  2. containing some kind of heating element to keep cold things cold.

  3. keeps hot things hot by not allowing heat to escape.

  4. All of the above

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Correct Option: C
Explanation:
A thermos flask maintains temperature of objects. It keeps hot things hot by not allowing heat to escape.
Thermos flask doesn't allow heat to escape from it via any mode of heat transfer i.e. conduction, convection, radiation. It does so by silver coating or polishing inner surface thin walls and vacuum between two walls.

Thermos flask prevents loss or gain of heat by

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. conduction only

  2. convections only

  3. radiation only

  4. all of the above

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Correct Option: C

Thermos flask, when closed, is an approximate

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. open system.

  2. closed system.

  3. isolated system.

  4. None of these

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Correct Option: C
Explanation:

An open system is a one which can exchange matter as well as energy with the surroundings. Eg: a beaker of water. A closed system is a one which can exchange only energy with the surroundings. Eg: a liquid in a closed bottle. An isolated system is a one which cannot exchange anything with the surroundings. Eg: Thermos Flask .

Liquid nitrogen is stored at $77K$ in a vacuum flask. The surrounding atmospheric temperature in the lab is $33K$.

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. After a few days, the temperature of liquid nitrogen will increase.

  2. After a few days, the temperature of the lab will decrease.

  3. After a few days, the temperature of liquid nitrogen will decrease

  4. After a few days, the temperature of liquid nitrogen will remain unchanged.

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Correct Option: D
Explanation:
Liquid nitrogen is stored at $77K$ in vacuum flask. The surrounding atmosphere temperature of the lab is $33K$.
After a few days, the temperature of liquid nitrogen will remain unchanged. Because, vacuum flask is designed to prevent heat loss by conduction, convection and radiation. So, the temperature remains unchanged.

Which of the following is an insulating component in thermos flask?

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. plastic foam

  2. air

  3. vacuum

  4. All of the above

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Correct Option: D
Explanation:
Insulating component in thermos flask are plastic foam, air, vacuum.
As plastic foam is insulator, so to prevent heat to radiate plastic foam is used just after the inner layer, plastic foam is being polished to reflect the inner heat inside, as air is bad conductor of heat it does not conduct heat just outside the outer layer. Vacuum is poor conductor of heat. It is situated between two layers, which prevents heat conduction through convection.