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Applications of insulation - class-IX

Description: applications of insulation
Number of Questions: 16
Created by:
Tags: temperature and heat heat clothes - our necessity transfer of heat physics heat transfer properties of bulk matter thermal properties of matter
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If we keep pop corn in a pressure cooker on a flame, heat is transferred from flame to corn by :

  1. Conduction

  2. Radiation

  3. Convection

  4. None


Correct Option: A
Explanation:

The direct contact of cooker and corn is an example of conduction.

The molecules of medium vibrate about their mean positions during heat transfer in the process of

  1. Conduction

  2. Radiation

  3. Convection

  4. None


Correct Option: A
Explanation:

The molecules of medium transfer heat as they vibrate about mean position in conduction.
The molecules of medium absorb heat, they rise and other molecules of medium come to take their place convection
In radiation, medium does not play role.

Air is a bad conductor of heat because:

  1. it's molecules are in continuous contact with each other.

  2. it's molecules are not in continuous contact with each other

  3. it's molecules absorb all the heat

  4. it's molecules are moving randomly due to Brownian motion


Correct Option: B
Explanation:
Air is a bad conductor of heat because it's molecules are not in continuous contact with each other.
Air molecules are too far to disperse heat energy to one another efficiently. Heat is conducted by molecules and atoms that are very closely bonded together and vibrating at high frequency.

.................. surface absorbs more heat than any other surface under identical conditions.

  1. White & Shiny

  2. White & Rough 

  3. Black & Rough

  4. Yellow & Shiny


Correct Option: C
Explanation:
Black & rough surface absorbs more heat than any other surface under identical conditions.
Black surface absorbs all the radiations more easily than any surface as its absorptivity is $1$.

The heat transfer in air is poor because

  1. it take place mainly due to convection

  2. it take place mainly due to conduction

  3. it take place mainly due to radiation

  4. all of the above


Correct Option: A
Explanation:

Air is a gas and its molecules are far apart from each other. So, this is not a good condition for conduction. Also, air being a non-metal doesn't have free electrons for conduction. Hence option B is not applicable.

C is also not applicable because radiation doesn't need any medium. Air being a fluid, convection can take place through it. But convection is not a very fast mode of transfer of heat.

Seema is planning a trip to Kashmir this summer. Which of the following clothes should she definitely pack?

  1. Denim Jacket

  2. Leather pants

  3. Woolen sweater

  4. Cotton shirt


Correct Option: C
Explanation:

She must pack the woolen sweater, because even in summer; Kashmir's climate will definitely too much cool. As wool is good insulator of heat; it insulates body from the surrounding. And the air which is trapped between woolen fabrics. It prevents the flow of heat from the body; as air is also bad conductor of heat. So as a result the heat present in the body remains trapped in the body; it can't escape to atmosphere.

Which of the following is not a valid reason for using cotton clothes in Summer ?

  1. Cotton clothes attract cool air.

  2. Cotton clothes absorb sweat from the body.

  3. Cotton exposes the sweat to atmosphere for evaporation

  4. Cotton is light in weight.


Correct Option: A
Explanation:

We wear cotton clothes during summer as cotton absorbs sweat from the body exposing to the atmosphere for easy evaporation. As we tend to sweat more during summer and cotton fabric absorb sweat and help body to cool down. Cotton allows better air circulation which helps to absorb and removing body moisture caused by sweat via evaporation cotton fabric is very light in weight.

Why do we wear cotton clothes in Summer ?

  1. Cotton is a bad conductor of heat and doesn't allow passage of warmer air near body.

  2. Cotton is a good conductor of heat and allows body heat to escape in the atmosphere.

  3. Cotton absorbs sweat from the body, exposing it to atmosphere for easy evaporation

  4. None of the above


Correct Option: C
Explanation:

We wear cotton clothes during summer as cotton absorbs sweat from the body, exposing to the atmosphere for easy evaporation. As we tend to sweat more during summer and cotton fabric absorbs sweat and help body to cool down. Cotton allows better air circulation which helps to absorb and removing body moisture caused by sweat via evaporation.

Which of the following is a wrong pair of clothes worn during a particular season ?

  1. Cotton clothes during summer

  2. Woolen clothes during winter

  3. Dark colored clothes during summer

  4. Polyester raincoats during Rainy season


Correct Option: C
Explanation:

Dark coloured clothes during summer is a wrong pair of clothes. As during summer, heat present in the atmosphere and surrounding is too much. And when dark colored clothes are the worm, as we know dark color absorbs more heat than any other color. So it will increase the heat felt by our body during summer.

Wool is used in making garments used in winter because

  1. Wool is a good conductor of heat

  2. Wool is a bad conductor of heat

  3. Air, trapped in between the wool fibres, prevents the flow of heat from our body to the cold surroundings.

  4. Both B and C


Correct Option: D
Explanation:

Wool is used in making garments used in winter because wool is bad conductor of heat; it insulates the body from the surrounding. And the air which is trapped in between the wool fibers; prevents the flow of heat from our body to the cool surrounding. As air is the bad conductor of heat too it also insulates the body with wool.

Which of the following fabrics is preferred for winter garments ?

  1. Nylon

  2. Cotton

  3. Wool

  4. Silk


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 ?

  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


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 ?

  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.


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.

  1. Shifts towards right

  2. Shifts towards left

  3. Remains unchanged

  4. Remains at zero


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?

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

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

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

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


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.

  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


Correct Option: B
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