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
Two spherical black bodies have radii r1 and r 2. Their surface temperatures are T1 and T 2. If they radiate same power then r2r1 is
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, λ0. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 34λ0, the power radiated by it becomes nP. The value of n is
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 is U1, at wavelength 500  nm is U2 and that at 1000 nm is U3. Wien's constant, b=2.88×106 nm K. Which of the following is correct?
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
EASY
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
Ordinary bodies A and B radiate maximum energy with wavelength difference 4 μm. The absolute temperature of body A is 3 times that of B. The wavelength at which body B radiates maximum energy is
EASY
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
If the emission rate of a blackbody at 0 °C is R , then the rate of emission at 273 °C is
EASY
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
The electromagnetic waves that cause greenhouse effect are
HARD
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
The maximum wavelength of radiation emitted by a star is 289.8 nm. Then intensity of radiation for the star is (Given : Stefan’s constant = 5.67×10-8 W m-2 K-4 , Wien’s constant, b=2898 μm K)
EASY
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
A black body has maximum wavelength λm 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 T1, T2, T3, respectively, are shown in the figure. Their temperatures are such that

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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 T0. The initial temperature of the sphere is 3T0. If the specific heat of the material of the sphere varies as αT3 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 2T0 will be

(σ is Stefan Boltzmann constant)

MEDIUM
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
Three stars A, B, C have surface temperatures TA, TB,TC  respectively. Star A appears bluish, star B appears reddish and star C yellowish. Hence,
HARD
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
Parallel rays of light of intensity I=912 Wm-2 are incident on a spherical black body kept in surroundings of temperature 300 K. Take Stefan-Boltzmann constant σ=5.7×10-8 Wm-2 K-4 and assume that the energy exchange with the surroundings is only through radiation. The final steady state temperature of the black body is close to
EASY
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
For any material, if R, T and A represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then for a blackbody which one of the following is true
HARD
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
A human body has a surface area of approximately 1 m2. The normal body temperature is 10 K above the surrounding room temperature T0 . Take the room temperature to be T0=300 K . For  T0=300 K, the value of σT4=460 W m-2(where σ is the Stefan-Boltzmann constant). Which of the following options is/are correct?
EASY
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law
If temperature of a black body increases from 300 K to 900 K, then the rate of energy radiation increases by
HARD
Physics>Heat and Thermodynamics>Heat Transfer>Wien’s Displacement Law

The filament of a light bulb has surface area 64 mm2. The filament can be considered as a black body at temperature 2500 K emitting radiation like a point source when viewed from far. At night the light bulb is observed from a distance of 100 m. Assume the pupil of the eyes of the observer to be circular with radius 3 mm. Then:

(Take Stefan-Boltzmann constant =5.67×10-8 W m-2 K-4, Wiens' displacement constant =2.90×10−3 m K, Planck's constant =6.60×10−34 J s, speed of light in vacuum =3.00×108 m s−1)

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 3×10-3 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 Tp, TQ and TR are the respective absolute temperatures of P , Q and R , then it can be concluded from the above observations that :