Thermal Properties of Matter

The power radiated by a black body is P and it radiates maximum energy at wavelength, 0. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 34 0, the power radiated by it becomes nP. The value of n is

1. 34
2. 43
3. 25681
4. 81256

A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be

1. 450
2. 1000
3. 1800
4. 225

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?

1. U1 > U2
2. U2 > U1
3. U1 = 0
4. U3 = 0

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

1. TP < TR < TQ
2. TP < TQ < TR
3. TP > TQ > TR
4. TP > TR > TQ

A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using

1. Kirchhoff's Law
2. Newton's Law of cooling
3. Stefan's Law
4. Wien's displacement Law

If the radius of a star is R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q?

1. Q4 2
2. ( Q4 2 )-1/2
3. ( 4 2Q )1/4
4. ( Q4 2 )1/4

The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, whose outer surface radiates as a black body at a temperature T K is given by

1. 2T4R2
2. 2T44 2
3. 2T4R4
4. 4 2T4R2

Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is where is the Stefan's constant.

1. r2 (t + 273)44 2
2. 16 2r2 4R2
3. r2 (t + 273)4R2
4. 4 2 4R2

A black body at 227 C radiates heat at the rate of 7 cal/cm2 s. At a temperature of 727 C, the rate of heat radiated in the same units will be

1. 50
2. 112
3. 80
4. 60

Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is where is the Stefan's constant.

1. r2 (t+273)44 2
2. 16 2r2 4R2
3. r2 (t+273)4R2
4. 4 2 4R2

A black body is at 727 . It emits energy at a rate which is proportional to

1. (1000)4
2. (1000)2
3. (727)4
4. (727)2

A black body at 1227 emits radiations with maximum intensity at a wavelength of 5000 A. If the temperature of the body is increased by 1000 , the maximum intensity will be observed at

1. 3000 A
2. 4000 A
3. 5000 A
4. 6000 A

If m denotes the wavelength at which the radiative emission from a black body at a temperature T K is maximum, then

1. m T4
2. m is independent of T
3. m T
4. m T-1

Unit of Stefan's constant is

1. watt m2 K4
2. watt m2/K4
3. watt/m2 K
4. watt/m2K4

For a black body at temperature 727 , its radiating power is 60 watt and temperature of surrounding is 227 . If temperature of black body is changed to 1227 then its radiating power will be

1. 304 W
2. 320 W
3. 240 W
4. 120 W

Which of the following is closest to an ideal black body?

1. lamp black
2. cavity maintained at constant temperature
3. platinum black
4. a lump of charcoal heated to high temperature.

The Wien's displacement law expresses relation between

1. wavelength corresponding to maximum energy and temperature
2. radiation energy and wavelength
3. temperature and wavelength
4. colour of light and temperature.

A black body emits maximum energy at wavelength m at 2000 K. Its corresponding wavelength at 3000 K will be

1. 32 m
2. 23 m
3. 1681 m
4. 8116 m