Thermal Properties of Matter · Question 30

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

The two ends of a rod of length L and a uniform cross-sectional area A are kept at two temperatures T1 and T2 (T1 > T2). The rate of heat transfer, dQdt through the rod in a steady state is given by :

1. dQdt = k(T1 - T2)LA
2. dQdt = kLA(T1 - T2)
3. dQdt = kA(T1 - T2)L
4. dQdt = kL(T1 - T2)A

On a new scale of temperature (which is linear) and called the W scale, the freezing and boiling points of water are 39 and 239 respectively. What will be the temperature on the new scale, corresponding to a temperature of 39 on the Celsius scale ?

1. 200
2. 139
3. 78
4. 117

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