Tag: transfer of heat

Questions Related to transfer of heat

Which of the following fabrics is preferred for winter garments ?

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

  1. Nylon

  2. Cotton

  3. Wool

  4. Silk

Show answer
Correct Option: C
Explanation:

Wool is the fabric that is preferred for winter garments. As wool is bad conductor of heat. It insulates the body from the surrounding. And the air which is trapped in between the wool fibers; it prevents the flow of heat from our body to cool surrounding.

Which of the following is not a reason for using woolen clothes in Winter ?

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

  1. Wool is an insulator of heat.

  2. It traps a layer of air in its fabric.

  3. Air being an insulator doesn't allow body heat to escape into the atmosphere.

  4. All the above

Show answer
Correct Option: D
Explanation:

Reason behind using woolen clothes during winter is that wool is the bad conductor of heat, it insulates the body from the surrounding. And the air which is trapped between woolen fabrics, prevents the flow of heat from the body as air is a bad conductor of heat too. So as a result the heat present in the body remains trapped in the body, it can't escape to atmosphere.

How does air trapped by the woolen fabric help ?

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

  1. Air is a good conductor of heat and allows warm air to come near body

  2. Air is a bad conductor of heat and allows body heat to escape into atmosphere

  3. Air is a bad conductor of heat and doesn't allow body heat to escape into atmosphere

  4. Air is a good conductor of heat and doesn't allow cool air to come near body.

Show answer
Correct Option: C
Explanation:

Air trapped by the woolen fabric help us during winter. As air is bad conductor of heat and doesn't allow body heat to escape into atmosphere. The heat stored inside the body does not goes out as wool and air acts as a layer of insulator. And body heat is not escaped from the body.

When a metal conductor connected to left gap of a meter bridge is heated, the balancing point.

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

  1. Shifts towards right

  2. Shifts towards left

  3. Remains unchanged

  4. Remains at zero

Show answer
Correct Option: A
Explanation:

When resistor is heated its resistance increases hence the balancing point will shift towards right.

Which of the following circular rods (given radius r and length l), each made of the same material and whose ends are maintained at the same temperature will conduct most heat?

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

  1. $r=r _0;l=l _0$

  2. $r=2r _0;l=l _0$

  3. $r=r _0;l=2l _0$

  4. $r=2r _0;l=2l _0$

Show answer
Correct Option: B
Explanation:

Heat is given by $H=KA\Delta \theta _x=K\pi r^2 \dfrac{\Delta \theta} {l}$

For option B the value of $H$ will be more.

A shining metallic ball with a small black spot on its surface is heated to very high temperature and then quickly taken to a dark room. Then.

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  1. Both appear equally bright

  2. The spot appears brighter than the ball

  3. The spot appears darker than the ball

  4. Both are invisible in the dark room

Show answer
Correct Option: B

A thermos flask is designed to prevent the contents of the flask from losing heat. Which of the following statements concerning the design of thermos flasks is incorrect?

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. The stopper helps reduce heat loss by convection

  2. The glass walls are silver coated to reduce emitted radiation

  3. The flask is designed to prevent heat loss by conduction, convection and radiation

  4. The vacuum between the glass walls prevents heat loss by preventing radiation

Show answer
Correct Option: D
Explanation:
Yes, thermoflask is designed to prevent  the contents of the flask from losing heat.
The stopper, i.e. vacuum between double walls of thermoflask prevents heat transfer through convection.
The glass walls are silver coated because it reduces emitted radiation when they are silver coated i.e. made shiny. And we know that shiny surfaces reflects all the heat so all the heat is being reflected inside the walls and heat remains unaffected. And the thinesss of glass walls will stop heat entering or leaving the flask by conduction.
So, the flask is designed to prevent heat loss by conduction, convection and radiation.

A                is a storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. Closed flask

  2. Vacuum flask

  3. Conducting flask

  4. None of these

Show answer
Correct Option: B
Explanation:

A thermoflask is a storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. As thermoflask is designed to prevent heat loss by conduction, convection and radiation.

Vacuum in a vacuum flask prevents heat transfer through process of-

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. Conduction only

  2. Conduction and Convection

  3. Convection only

  4. Radiation only

Show answer
Correct Option: B
Explanation:
Vacuum in a vacuum flask prevents heat transfer through process of conduction and convection.
It is so because, in conduction there needs a direct contact for transfer of heat and there is vaccum between two layers, so conduction can't  transfer heat in this case. And in convection, heat is transferred by molecular motion in fluid (liquid or gas). But due to vaccum's presence between two layers, molecular motion is not possible So convection is also impossible for this case.

The silver coating on the inner bottle of a thermos flask

thermo flask thermos flask heat energy transfers transfer of heat physics

  1. prevents heat transfer by conduction

  2. prevents heat transfer by convection

  3. prevents heat transfer by radiation

  4. prevents heat transfer by absorption

Show answer
Correct Option: C
Explanation:
Due to the silver coating on the inner bottle, a shiny surface is formed. And these shiny surface act as a good reflector of heat 
As a result, they prevent the transfer of heat by radiation.