Tag: temperature and heat

Questions Related to temperature and heat

In which mode of transfer of heat molecules pass on heat energy to neighbouring molecules without actually moving from their positions?

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. convection

  2. radiation

  3. conduction

  4. none of these

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Correct Option: C
Explanation:
Conduction is the mode of heat transfer of heat molecules pass on heat energy to neighbouring molecules without actually moving from their positions.
Conduction is the transfer of heat from one substance to another by direct contact without mixing of masses.

In a steady state the temperature of the ends A and B of a 20 cm long rod AB is 100$^o$C and 0$^o$C. The temperature at the point c distant 9 cm from a is :

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $45^o$C

  2. $55^o$C

  3. $60^o$C

  4. $65^o$C

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Correct Option: B
Explanation:
Temperature increasing per unit length $=\cfrac{100-0}{20}=5^oC/cm$
Temperature at $9cm$ from $a \\ =100^oC-(5^oC/cm\times 9cm) \\ =55^oC$

Sea and land breezes are caused because of :

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. convection

  2. cyclones

  3. rains

  4. conduction

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Correct Option: A
Explanation:

All wind is caused by a pressure gradient. In the case of land or sea breeze, the pressure gradient is due to the different heating and cooling rates of the area.

Lake or sea breeze and land breeze are on a comparatively small scale when viewing meteorological events. This is important to note because large scale heating and small scale heating work differently. In the case of small scale heating, the increase in heat causes an increase in volume which in turn lowers the pressure in that area.
In the morning the land heats up much faster than the water. This eventually results in a pressure gradient with a lower pressure on the land due to the quicker heating. Air moves from the water to the land in the form of a sea breeze.

After sunset, the land cools much quicker than the water. As a result, the volume of the air over the water is higher and the pressure decreases. Ar then moves over the water as a land breeze.

Conduction cannot take place in:

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. Copper

  2. Iron

  3. Aluminium

  4. Vacuum

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Correct Option: D
Explanation:

A solid medium is required for conduction to take place. Since, vaccum does not have a medium, conduction does not take place.

Transmission of heat by the movement of heated particles is called

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. Conduction

  2. Convection

  3. Radiation

  4. Regelation

  5. Expansion

Show answer
Correct Option: B
Explanation:

Convection is a mode of heat transfer where in the molecules near the heat source get heated up, they expand , becomes less dense , and rise upwards .whereas the relatively colder sink to the bottom and eventually get heated up. Thus transmission of heat by the movement of heated particles of heat particles is called convection.

The only liquid which is a good conductor of heat is-

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. water

  2. turpentine

  3. alcohol

  4. mercury

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Correct Option: D
Explanation:
The liquid which is good conductor of heat is mercury.
 Thermal conductivity is $8.30W/(mK)$ of mercury.

State whether given statement is True or False
Air conducts heat

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. True

  2. False

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Correct Option: B
Explanation:

False, air do not conducts heat.

But air is poor conductor of heat because its molecules are not in continuous contact with one another unlike a solid. Heat by conduction passes more quickly in solid because the molecules vibrations immediately affect the neighbours. Air molecules only transfer energy upon collision and the collision time is too small for significant energy transfer to occur. Heat transfer in air is mainly due to convection, which in general is less efficient than in conduction.

Give reason : Birds puff up their feathers in winter 

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. so that they can trap more air

  2. so that can develop charge

  3. cant say

  4. so that friction reduces

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Correct Option: A
Explanation:

Birds puff up their feathers in winter because by doing so they trap a large amount of air in their body which in turn acts as an insulator and does not allow the heat from their bodies to flow out

Using a heating blanket to get warm is an example of-

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. Conduction

  2. Convection

  3. Radiation

  4. none of these

Show answer
Correct Option: A
Explanation:
Using a heating blanket to get warm is example of conduction.
As conduction is the transfer of heat from one body to another by direct contact without mixing of masses. When we cover ourselves with blanket, there is direct contact. And blanket insulates the heat present in the body and does not out heat to escape and loose warmth.

Same quantity of ice is filled in each of the two metal containers P and Q having the same size, shape and wall thickness but made of different materials. The containers are kept in identical surroundings. The ice in P melts completely in time $t _1$ whereas that in Q takes a time $t _2$. The ratio of thermal conductivities of the materials of P and Q is

physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

  1. $t _2 : t _1$

  2. $t _1 : t _2$

  3. $t _1^2 : t _2^2$

  4. $t _2^2 : t _1^2$

Show answer
Correct Option: A
Explanation:

The power transported per unit area is given as

$\dfrac{\Delta Q}{A\Delta t}=-\kappa\dfrac{\Delta T}{\Delta x}$
Thus $\Delta Q=-\kappa \Delta tA\dfrac{\Delta T}{\Delta x}$
Same amount of heat was needed to melt ice in both P and Q. Hence 
$\kappa _{P}t _1=\kappa _Qt _2$
$\implies \dfrac{\kappa _P}{\kappa _Q}=\dfrac{t _2}{t _1}$