Thermal Properties of Matter · Question 34

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

Which of the following rods, (given radius r and length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat?

1. r = r0, l = l0
2. r = 2r0, l = l0
3. r = r0, l = 2l0
4. r = 2r0, l = 2l0

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

Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities K and 2K, respectively. The equivalent thermal conductivity of the slab is

1. 23K
2. 2K
3. 3K
4. 43K

Unit of Stefan's constant is

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

Consider two rods of same length and different specific heats (S1, S2), conductivities (K1, K2) and area of cross-sections (A1, A2) and both having temperatures T1 and T2 at their ends. If rate of loss of heat due to conduction is equal, then

1. K1A1 = K2A2
2. K1A1S1 = K2A2S2
3. K2A1 = K1A2
4. K2A1S2 = K1A2S1

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.