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

The spectral energy distribution of star is maximum at twice temperature as that of sun. The total energy radiated by star is 

(1) Twice as that of the sun

(2) Same as that of the sun

(3) Sixteen times as that of the sun

(4) One sixteenth of sun

A bucket full of hot water cools from 75$°\mathrm{C}$ to 70$°\mathrm{C}$ in time ${\mathrm{T}}_1$, from 70$°\mathrm{C}$ to 65$°\mathrm{C}$ in time ${\mathrm{T}}_2$  and from 65$°\mathrm{C}$ to 60$°\mathrm{C}$ in time ${\mathrm{T}}_3$, then 
(1) ${\mathrm{T}}_1={\mathrm{T}}_2={\mathrm{T}}_3$              

(2) ${\mathrm{T}}_1>{\mathrm{T}}_2>{\mathrm{T}}_3$

(3) ${\mathrm{T}}_1<{\mathrm{T}}_2<{\mathrm{T}}_3$               

(4) ${\mathrm{T}}_1>{\mathrm{T}}_2<{\mathrm{T}}_3$

Consider two hot bodies, ${\mathrm{B}}_1$ and ${\mathrm{B}}_2$ which have temperatures of \(100^{\circ}\mathrm{C}\)$\mathrm{}$ and \(80^{\circ}\mathrm{C}\)$\mathrm{}$ respectively at t=0. The temperature of the surroundings is \(40^{\circ}\mathrm{C}\)$\mathrm{}$. The ratio of the respective rates of cooling ${\mathrm{R}}_1$ and ${\mathrm{R}}_2$ of these two bodies at t = 0 will be:
1. ${\mathrm{R}}_1:{\mathrm{R}}_2=3:2$
2. ${\mathrm{R}}_1:{\mathrm{R}}_2=5:4$
3. ${\mathrm{R}}_1:{\mathrm{R}}_2=2:3$
4. ${\mathrm{R}}_1:{\mathrm{R}}_2=4:5$

Newton's law of cooling is a special case of
(1) Stefan's law           

(2) Kirchhoff's law

(3) Wien's law             

(4) Planck's law