EASY

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Following graphs show the variation in the intensity of heat radiations by the black body and frequency at a fixed temperature. Choose the correct option.

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Important Questions on Heat Transfer

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

If the emission rate of a blackbody at

0 ° C

R

, then the rate of emission at

273 ° C

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

The power radiated by a black body is P and it radiates maximum energy at wavelength,

λ_{0}

. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength

\frac{3}{4} λ_{0}

, the power radiated by it becomes nP. The value of n is

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Two spherical black bodies have radii

r_{1}

and

r_{2}

. Their surface temperatures are

T_{1}

and

T_{2}

. If they radiate same power then

\frac{r_{2}}{r_{1}}

HARD

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

A black coloured solid sphere of radius $R$ and mass $M$ is inside a cavity with a vacuum inside. The walls of the cavity are maintained at temperature $T_{0}$ . The initial temperature of the sphere is $3 T_{0}$ . If the specific heat of the material of the sphere varies as $α T^{3}$ per unit mass with the temperature $T$ of the sphere, where $α$ is a constant, then the time taken for the sphere to cool down to temperature $2 T_{0}$ will be

( $σ$ is Stefan Boltzmann constant)

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Ordinary bodies

A

and

B

radiate maximum energy with wavelength difference

4 μ m

. The absolute temperature of body

A

3

times that of

B

. The wavelength at which body

B

radiates maximum energy is

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

A spherical black body with a radius of

12 cm

radiates

450 W

power at

500 K

. If the radius were halved and the temperature doubled, the power radiated in watt would be

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

A black body is at a temperature of

5760 K.

The energy of radiation emitted by the body at wavelength

250 nm

U_{1}

, at wavelength

500 nm

U_{2}

and that at

1000 nm

U_{3}

. Wien's constant,

b = 2.88 \times 10^{6} nm K.

Which of the following is correct?

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Two black bodies $A$ and $B$ have equal surface areas and are maintained at temperatures $27 ° C$ and $177 ° C$ respectively. What will be the ratio of the thermal energy radiated per second by $A$ to that by $B ?$

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

A black body has maximum wavelength

λ_{m}

at temperature

2200 K .

Its corresponding wavelength at temperature

3300 K

will be

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

The plots of intensity versus wavelength for three black bodies at temperature $T_{1}$ , $T_{2}$ , $T_{3}$ , respectively, are shown in the figure. Their temperatures are such that

Question Image

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

If temperature of a black body increases from

300 K

900 K

, then the rate of energy radiation increases by

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Three stars

A, B, C

have surface temperatures

T_{A}, T_{B}, T_{C}

respectively. Star A appears bluish, star

B

appears reddish and star

C

yellowish. Hence,

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Two spheres

S_{1}

and

S_{2}

have same radii but temperatures

T_{1}

and

T_{2}

respectively. Their emissive power is same and emissivity is in the ratio

1 : 4

Then the ratio of

T_{1}

T_{2}

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Solar energy is incident normally on the earth's surface at the rate of about

1 .4 kW m^{- 2}

. The distance between the earth and the sun is

1 .5 \times 10^{11} m

. Energy

(E)

and mass

(m)

are related by the Einstein equation,

E = m c^{2}

where

c = (3 \times 10^{8} m s^{- 1})

is the speed of light in free space. The decrease in the mass of the sun is

MEDIUM

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Earth receives Sun's radiation at the rate of

P W m^{- 2}

. Mean distance between the Sun and the Earth is

r m

. Radius of the Sun is

R m

. If Stefan's constant is

σ

(in

SI

units), surface temperature of the Sun, in kelvin, is

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Prevost's theory of heat exchange is not applicable at temperature

HARD

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

Three large identical plates are kept parallel to each other. The outer two plates are maintained at temperatures

T

and

2 T

, respectively. The temperature of the middle plate in steady state will be close to

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

The wavelength of the radiation emitted by a black body is

6 mm

and Wein's constant is

3 \times 10^{- 3} mK .

Then temperature of black body is

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

In the case of black body for energy distribution, energy radiated by a blackbody which is given by, Planck's formula reduces to Rayleigh Jean's formula for

EASY

Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

On observing light from three different stars

P

Q

and

R

, it was found that intensity of violet colour is maximum in the spectrum of

P

, the intensity of green colour is maximum in the spectrum of

R

and the intensity of red colour is maximum in the spectrum of

Q

. If

T_{p}, T_{Q}

and

T_{R}

are the respective absolute temperatures of

P

Q

and

R

, then it can be concluded from the above observations that :

Following graphs show the variation in the intensity of heat radiations by the black body and frequency at a fixed temperature. Choose the correct option.

Important Questions on Heat Transfer

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