Tag: heat and heat transfer

Questions Related to heat and heat transfer

A geyser heats water flowing at the rate of 4 litre per minutes from 30 C to 85 C. If the geyser operates on gas burner then the amount of heat used per minute is :

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. $9.24\times { 10 }^{ 5 }$J

  2. $6.24\times { 10 }^{ 7 }$J

  3. $9.24\times { 10 }^{ 7 }$J

  4. $6.24\times { 10 }^{ 5 }$J

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Correct Option: A
Explanation:

For one minute

$H=mC\theta$
$=4kg\times 4200\times55\=924000J\=9.24\times 10^5j$

A 2 m long wire of resistance 4 ohm and diameter 0.64 mm is coated with plastic insulation of thickness 0.06 mm, when a current of 5 ampere flows through the wire, find the temperature difference across the insulation in steady state if $k=0.16\times { 10 }^{ -2 }cal/\left( cm{ C }^{ 0 }sec \right) $ 

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. ${ 3 }^{ \circ }C$

  2. ${ 2 }^{ \circ }C$

  3. ${ 4 }^{ \circ }C$

  4. ${ 1 }^{ \circ }C$

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Correct Option: A

M g of ice at ${ 0 }^{ \circ  }C$ is mixed with M g of water at ${ 10 }^{ \circ  }C.$ The final temperature is

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. ${ 8 }^{ \circ }C$

  2. ${ 6 }^{ \circ }C$

  3. ${ 4 }^{ \circ }C$

  4. ${ 0 }^{ \circ }C$

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Correct Option: A

Name a medium which is a good insulator of heat.

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. Still (or trapped) air

  2. Oil

  3. Steam

  4. solid copper

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Correct Option: A
Explanation:
Trapped(still) air is good insulator.
Thermal conductivity of air is small as compared to solid and liquid. Eg- glass conducts 30 times more power per unit distance per unit temperature than air.
The less dense the material, the less thermal conductivity. And gas(air) is least dense than solid and liquid.

A cotton sheet is ironed with hot electricity. How is energy transferred through the metal base of the iron to the sheet?

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. by conduction only

  2. by convection only

  3. by radiation only

  4. by convection and radiation only

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Correct Option: A
Explanation:
Conduction occurs when two objects at different temperatures are in contact with each other. Heat flows from the warmer to the cooler object until they are both at the same temperature.
The iron and cotton sheet is in contact with each other so, there is conduction between them.

Energy transformation while ironing clothes takes out their wrinkles and makes them smooth. This takes the heat, which is one type of energy. In the iron, electrical energy is used, and it is transformed into heat energy.

In the following solids thermal conductivity is maximum for :

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. copper

  2. aluminium

  3. gold

  4. silver

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Correct Option: D
Explanation:

This is a knowledge based question; also remember that copper is used in electrical wiring only because it is cheaper than silver; copper has lower conductivity than silver.

Two layers of cloth of equal thickness provide warmer covering than a single layer of cloth of double the thickness, because they :

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. behave like a thermos

  2. have lesser thickness

  3. allow heat from atmosphere to the body

  4. enclose between them a layer of air

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Correct Option: D
Explanation:

Air is a bad conductor of heat, hence if layer of air is isolated between two layers of cloth, warmer covering will be provided than if only one layer of cloth, where only body is isolated from surrounding air by cloth. 

Thermoflasks and doors of refrigerators have two layered structure with an insulator in between so as:

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. to allow more heat to pass through it

  2. not to let heat flow through it

  3. to make it stronger

  4. to beautify it

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Correct Option: B
Explanation:

Insulator between the two layers prevent the heat exchange.

Mercury is generally used in thermometer because it has a

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. High fluidity

  2. High density

  3. High coefficient of expansion

  4. High specific heat

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Correct Option: C
Explanation:

Most metals are good conductors of heat and they are solids at room temperature. Mercury is the only one in liquid state at room temperature. It's used in thermometers because it has high coefficient of expansion. Hence, the slightest change in temperature is notable when it's used in a thermometer.

Which of the following is a good conductor of heat?

physics heat energy transfers heat and heat transfer heat energy transfer transfer of heat

  1. Plastic

  2. Mercury

  3. Water

  4. Alcohol

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Correct Option: B
Explanation:

Mercury is categorized under metasl and we know that metals conduct heat better than non-metals.

So mercury is the answer.