Tag: modes of heat transfer - conduction

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

Sea and land breezes are caused because of :

  1. convection

  2. cyclones

  3. rains

  4. conduction
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

Transmission of heat by the movement of heated particles is called

  1. Conduction

  2. Convection

  3. Radiation

  4. Regelation

  5. Expansion
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

State whether given statement is True or False
Air conducts heat

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Give reason : Birds puff up their feathers in winter 

  1. so that they can trap more air

  2. so that can develop charge

  3. cant say

  4. so that friction reduces
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

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

  1. Conduction

  2. Convection

  3. Radiation

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice physics temperature and heat modes of heat transfer - conduction conduction heat and modes of heat transfer

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

  1. $t _2 : t _1$

  2. $t _1 : t _2$

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

  4. $t _2^2 : t _1^2$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 
$\kappa _{P}t _1=\kappa _Qt _2$
$\implies \dfrac{\kappa _P}{\kappa _Q}=\dfrac{t _2}{t _1}$

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

Two thermometers are used to record the temperature of a room. If the bulb of one is wrapped in wet hanky:

  1. The temperature recorded by both will be same.

  2. The temperature recorded by the wet-bulb thermometer will be greater than that recorded by the other.

  3. The temperature recorded by dry-bulb thermometer will be greater than that recorded by the other

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The thermometer whose bulb is wrapped by wet hanky; undergoes evaporation process; and we know that evaporation results in cooling, so the wet bulb, thermometer will record less temperature than that of dry bulb thermometer.

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

Two plates of same thickness form a composite plate. The temperature on one side of the plate is $0^0 C$. If the ratio of thermal conductivities is 3 : 1 and the plate with higher thermal conductivity has one of its faces at $0^0 C$, then the temperature of the interface is 

  1. $45^0 C$

  2. $40^0 C$

  3. $20^0 C$

  4. $15^0 C$
Reveal answer Fill a bubble to check yourself
D Correct answer