Tag: temperature and heat

Questions Related to temperature and heat

Two rods of equal length and area of cross-sectional are kept parallel and lagged between temperature $ 20^o C and 80^oC $ The ration of the effective thermal conductivity to that of the first rod is
 $ \left[ the\quad ration\left( \frac { K _ 1 }{ K _ 2 }  \right) =\frac { 3 }{ 4 }  \right]  $

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

  1. 7 : 4

  2. 7 : 6

  3. 4 : 7

  4. 7 : 8

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Correct Option: A

In engines water is used as coolant, because

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

  1. It good conductor of heat energy.

  2. It has low density.

  3. It has LOW specific heat.

  4. It's bad conductor of heat energy.

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Correct Option: D

Fix a lighted candle on a table. Put a glass chimney over the candle in such a way that air can enter the chimney from below. What happens to the flame? 

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

  1. Continues burning

  2. Flickers off

  3. Flickers off and give smoke

  4. None of these

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Correct Option: C

Two spheres of different materials one with double the radius and one - fourth wall thickness of the other, are filled with $r$ ice. If the time taken for complete melting ice in the large radius one is $25 minutes$ and that for smaller one is $16 minutes$, $r$ the ratio of thermal conductivity of the materials of larger sphere to the smaller sphere is $r$

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

  1. $4:5$

  2. $5:4$

  3. $25:1$

  4. $1:25$

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Correct Option: D

At a common temperature ,a block of wood and a block of metal feel equally cool or hot. The temperatures of metal and wood are

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

  1. $Less$ $than$ $the$ $temperature$ $of$ $the$ $body$

  2. $Equal$ $than$ $the$ $temperature$ $of$ $the$ $body$

  3. $Greater$ $than$ $the$ $temperature$ $of$ $the$ $body$

  4. $Either$ $(a)$ $or$ $(c)$

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Correct Option: B

Choose the correct experiment to demonstrate the transfer of heat by the process of conduction.

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

  1. Take two metal blocks of same size & shape and heat one of them to a considerable temperature, then allow both the blocks to touch each other, after a while, you will see the other block gets heated due to contact.

  2. Take two metal blocks of same size & shape and heat one of them to a considerable temperature, then keep the blocks separate, after a while you will see the other block gets heated due to contact.

  3. Take two metal blocks of same size & shape and heat one of them to a considerable temperature, then allow both the blocks to touch each other after the block get cooled down, after a while you will see the other block gets heated due to contact.

  4. None of above

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Correct Option: A
Explanation:
Take two metal blocks of same size & shape and heat one of them to a considerable temperature, then allow both the blocks to touch each other, after a while you will see the other block gets heated due to contact.

If a rod is in a variable state (not in steady state), then

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

  1. Temperature gradient remains constant

  2. Temperature of rod is function of time and distance from one of end

  3. Temperature of rod is only function of distance from one of end

  4. Temperature of rod is only function of time

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Correct Option: B

State true or false:
The more is the temperature difference of hot and cold body more slowly the heat flows from it into the cold body

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:
The amount of heat leaving the hot object will be equal to the amount of heat received by the colder object (assuming nothing else is around to receive some of the heat). The rate at which heat transfers from the hotter object to the colder object increases with the temperature difference between the objects.

By which of the following methods could a cup of hot tea lose heat when placed on metallic table in a class room
a) conduction
b) convection
c) radiation
d) evaporation of liquid.

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

  1. a, b

  2. b,c

  3. a,b,c

  4. a,b,c,d

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Correct Option: C
Explanation:

Conduction occurs through the walls of the cup.
Radiation occurs from the top surface.
Convection occurs at the top of the cup.
Evaporation of liquid also occurs.

The quantity of heat flowing for $10 \ s$ through a rod of length $40\ cm$, area $50 \ cm^{2}$ is $200\ J$. If the temperature difference at the ends of the rod is 80$^{o}$C , the coefficient of thermal conductivity of the rod in Wm$^{-1}$K$^{-1}$ is:

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

  1. $20$

  2. $60$

  3. $80$

  4. $120$

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Correct Option: A
Explanation:

$Q = 200$
$A = 50 \times 10^{-4}\ m^2$
${\theta}^{} _{1} = 80^\circ C    ;   \ \ {\theta}^{} _{2} = 0$
$t = 10\ s ; \ \    l  = 0.40\ m$
$Q = \dfrac{KA\Delta T t}{L}$
$200 = \dfrac{K  \times 50\times 10^{-4}\times    80\times    10}{0.4}$ 
$K = 20\ W/mK$