The radiation emitted by a star A is 10,000 times that of the sun. If the surface temperatures of the sun and the star A are 6000 K and 2000 K respectively, the ratio of the radii of the star A and the sun is 
1. 300 : 1                     

2. 600 : 1

3. 900 : 1                     

4. 1200 : 1

Star A has radius r surface temperature T while star B has radius 4r and surface temperature T/2. The ratio of the power of two stars, ${\mathrm{P}}_{\mathrm{A}}$:${\mathrm{P}}_{\mathrm{B}}$is 
(1) 16 : 1                           

(2) 1 : 16

(3) 1 : 1                             

(4) 1 : 4

Suppose the sun expands so that its radius becomes 100 times its present radius and its surface temperature becomes half of its present value. The total energy emitted by it then will increase by a factor of
(1) ${10}^4$                

(2) 625

(3) 256                 

(4) 16

If the temperature of the body is increased from \(-73^{\circ}\mathrm{C}\)$\mathrm{}$ to \(327^{\circ}\mathrm{C}\)$\mathrm{}$, then the ratio of energy emitted per second in both cases is:
1. 1 : 3                         
2. 1 : 81
3. 1 : 27                       
4. 1 : 9

If the sun’s surface radiates heat at \(6.3\times 10^{7}~\text{Wm}^{-2}\) ${\mathrm{}}^{}$then the temperature of the sun, assuming it to be a black body, will be:
\(\left(\sigma = 5.7\times 10^{-8}~\text{Wm}^{-2}\text{K}^{-4}\right)\)
1. \(5.8\times 10^{3}~\text{K}\)
2. \(8.5\times 10^{3}~\text{K}\)
3. \(3.5\times 10^{8}~\text{K}\)
4. \(5.3\times 10^{8}~\text{K}\)

The value of Stefan’s constant is 
(a) $5.67\times {10}^{-8} \mathrm{W}/{\mathrm{m}}^2-{\mathrm{K}}^4$                       (b) $5.67\times {10}^{-5} \mathrm{W}/{\mathrm{m}}^2-{\mathrm{K}}^4$
(c) $5.67\times {10}^{-11} \mathrm{W}/{\mathrm{m}}^2-{\mathrm{K}}^4$                      (d) None of these

Rate of cooling at 600K, if surrounding temperature is 300K is R. The rate of cooling at 900K is
(1) $\frac{16}{3}\mathrm{R}$                    

(2) 2R

(3) 3R                         

(4) $\frac{2}{3}\mathrm{R}$ 

A black body of surface area 10 ${\mathrm{cm}}^2$ is heated to 127°C and is suspended in a room at temperature 27°C. The initial rate of loss of heat from the body at the room temperature will be 
(1) 2.99 W               

(2) 1.89 W

(3) 1.18 W               

(4) 0.99 W

Two identical objects A and B are at temperatures ${\mathrm{T}}_{\mathrm{A}}$ and ${\mathrm{T}}_{\mathrm{B}}$ respectively. Both objects are placed in a room with perfectly absorbing walls maintained at temperatures T(${\mathrm{T}}_{\mathrm{A}}$>T>${\mathrm{T}}_{\mathrm{B}}$). The objects A and B attain temperature T eventually. Which one of the following is the correct statement?

(1) ‘A’ only emits radiations while B only absorbs them until both attain temperature

(2) A loses more radiations than it absorbs while B absorbs more radiations than it emits until temperature T is attained

(3) Both A and B only absorb radiations until they attain temperature T

(4) Both A and B only emit radiations until they attain temperature T

When the body has the same temperature as that of surroundings

(1) It does not radiate heat

(2) It radiates the same quantity of heat as it absorbs

(3) It radiates less quantity of heat as it receives from surroundings

(4) It radiates more quantity of heat as it receives heat from surroundings