Tag: physics

Questions Related to physics

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:

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

SI units of thermal conductivity are

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

  1. W/m - K.

  2. W/m

  3. W/K

  4. None

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Correct Option: A
Explanation:

From the formula:

Rate of heat flow $= \dfrac{(k \times A \times (Change\ of\ temp))}{Thickness}$
Units of $k$ are $W/m-K$.

The thermal conductivity of a rod depends on

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

  1. length

  2. mas

  3. area of cross section

  4. material of the rod

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Correct Option: D

Coefficient of thermal conductivity :

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

  1. depends upon nature of the material of the body

  2. is independent of dimensions of the body

  3. both 1 and 2

  4. only 1

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Correct Option: A
Explanation:

Coefficient of thermal conductivity of a rod is an intrinsic property. It depends on the material of the rod and not on the dimensions of the rod.