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What are Diathermanous and Athermanous substances?

Important Questions on Kinetic Theory of Gases and Radiation

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

The circuit below is used to heat water kept in a bucket.

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Assuming heat loss only by Newton's law of cooling, the variation in the temperature of the water in the bucket as a function of time is depicted by

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A body cools from

70 ° C

40 ° C

5

minutes. Calculate the time it takes to cool from

60 ° C

30 ° C

. The temperature of the surroundings is

20 ° C

MEDIUM

Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A liquid of mass

250 g

is kept warm in a vessel using an electric heater. The liquid is maintained at

57 ° C

when the power supplied by the heater is

30 W

and surrounding temperature is

27 ° C

. As the heater is switched off, it took

10 s

time for the temperature of the liquid to fall from

47 ° C

46.9 ° C

. The specific heat capacity of the liquid is

HARD

Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A body takes

4 \min

to cool from

61 ° C

59 ° C .

If the temperature of the surroundings is

30 ° C,

the time taken by the body to cool from

51 ° C

49 ° C

is:

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

If a piece of metal is heated to temperature

θ

and then allowed to cool in a room which is at temperature

θ_{0}

, the graph between the temperature

T

of the metal and time

t

will be closest to :

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A pan filled with hot food cools from

94 ° C

86 ° C

2 \min,

when the room temperature is

20 ° C .

The time taken for the food to cool from

86 ° C

74 ° C

will be

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A body cools from

80 ° C

50 ° C

after a time interval

Δ t

. Assuming that the surrounding temperature is

20 ° C .

the temperature of the body after time interval of

2 Δ t

MEDIUM

Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A body cools from

70 ° C

40 ° C

5 \min .

Calculate the time it takes to cool from

60 ° C

40 ° C .

The temperature of the surrounding is

20 ° C .

MEDIUM

Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

Certain quantity of water cools from

70^{o} C

60^{o} C

in the first

5

minutes and to

54^{o} C

in the next

5

minutes. The temperature of the surroundings is:

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A metallic sphere cools from

50 ° C

40 ° C

300 s

. If atmospheric temperature around is

20 ° C

, then the sphere's temperature after the nest

5

minutes will be close to:

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

In $5 minutes$ , a body cools from $75 ° C$ to $65 ° C$ at room temperature of $25 ° C .$ The temperature of body at the end of next $5 minutes$ is ${}^{\circ}C .$

MEDIUM

Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A body cools from a temperature

3 T

2 T

10

minutes. The room temperature is

T

. Assume that Newton's law of cooling is applicable. The temperature of the body at the end of next

10

minutes will be

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A liquid cools from

70 ° C

50 ° C

5

minutes. Find the time taken by the liquid to cool from

60 ° C

50 ° C

, if the temperature of the surrounding is constant at

30 ° C

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A cup of tea cools from

65.5 ° C

62.5 ° C

1

minute in a room at

22.5 ° C

. How long will it take to cool from

46.5 ° C

40.5 ° C

in the same room?

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A cup of coffee cools from

90 ° C

80 ° C

t \min

, when the room temperature is

20 ° C

. The time taken by a similar cup of coffee to cool from

80 ° C to 60 ° C

at a room temperature same at

20 ° C

is :

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A cube, a cylinder (of height equal to its diameter) and a sphere, all solid, are made of metal and are of identical mass. If all the three shapes having initial temperature

50 ° C

are put in a large reservoir of water at

10 ° C .

Which of the above three shapes cools the fastest?

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A body cools from

60 ° C

50 ° C

10 \min

. If room temperature is

25 ° C

, then the temperature of body at the end of next

10 \min

will be

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

A container with $1 kg$ of water in it is kept in sunlight, which causes the water to get warmer than the surroundings. The average energy per unit time per unit area received due to the sunlight is $700 W m^{- 2}$ and it is absorbed by the water over an effective area of $0.05 m^{2} .$ Assuming that the heat loss from the water to the surroundings is governed by Newton's law of cooling, the difference (in ${}^{\circ}C$ ) in the temperature of water and the surroundings after a long time will be_________. (Ignore effect of the container, and take constant for Newton's law of cooling $= 0.001 s^{- 1},$ Heat capacity of water $= 4200 J {kg}^{- 1} K^{- 1}$ )

(Approximate the answer to two decimal place)

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

Two identical beakers

A

and

B

contain equal volumes of two different liquids at

60 ° C

each and left to cool down. Liquid in

A

has density of

8 \times 10^{2} k g m^{- 3}

and specific heat of

2000 J k g^{- 1} K^{- 1}

while the liquid in

B

has density

10^{3} k g m^{- 3}

and specific heat of

4000 J k g^{- 1} K^{- 1}

. Which of the following best describes their temperature versus time graph schematically? (assume the emissivity of both the beakers to be the same)

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Physics>Heat and Thermodynamics>Kinetic Theory of Gases and Radiation>Absorption, Reflection and Transmission of Heat Radiation

Two bottles

A

and

B

have radii

R_{A}

and

R_{B}

and heights

h_{A}

and

h_{B}

respectively with

R_{B} = 2 R_{A}

and

h_{B} = 2 h_{A}

. These are filled with hot water at

60 ° C

. Consider that heat loss for the bottles takes place only from side surfaces. If the time the water takes to cool down to

50 ° C

t_{A}

and

t_{B}

for bottles

A

and

B

, respectively, then

t_{A}

and

t_{B}

are best related as,

What are Diathermanous and Athermanous substances?

Important Questions on Kinetic Theory of Gases and Radiation

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