Tag: physics

Questions Related to physics

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

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

  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.

Show answer
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 ?

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

  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

Show answer
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 ?

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

  1. Cotton clothes during summer

  2. Woolen clothes during winter

  3. Dark colored clothes during summer

  4. Polyester raincoats during Rainy season

Show answer
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

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

  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

Show answer
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 ?

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 permanent magnet in the shape of a thin cylinder of length $10$cm has magnetisation (M) $=10^6$A $m^{-1}$. It's magnetization current $I _M$ is?

physics electro-magnetism applications of electromagnets

  1. $10^5$A

  2. $10^6$A

  3. $10^7$A

  4. $10^8$A

Show answer
Correct Option: A
Explanation:

Given:

 The length of the thin cylinder is $10\ cm$.
The magnetization of the magnet is $10^6 A/m$

The magnetization current is given by:
$I _M=M\times l$

$I _M=10^6\times 0.1$

$\Rightarrow10^5\ A$