A hot and a cold body are kept in vacuum separated from each other. Which of the following cause decrease in temperature of the hot body ?

(1) Radiation

(2) Convection

(3) Conduction

(4) Temperature remains unchanged

For a perfectly black body, its absorptive power is

(1) 1                 

(2) 0.5

(3) 0                 

(4) Infinity

Certain substance emits only the wavelengths ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2, {\mathrm{\lambda }}_3$ and ${\mathrm{\lambda }}_4$ when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelengths ?
(a) ${\mathrm{\lambda }}_1$                      (b) ${\mathrm{\lambda }}_2$
(c) ${\mathrm{\lambda }}_1$ and ${\mathrm{\lambda }}_2$          (d)  ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2, {\mathrm{\lambda }}_3$ and ${\mathrm{\lambda }}_4$

As compared to the person with white skin, the person with black skin will experience 
(1) Less heat and more cold           

(2) More heat and more cold

(3) More heat and less cold             

(4) Less heat and less cold

Relation between emissivity e and absorptive power a is (for black body)
(1) e = a                     

(2) $\mathrm{e}=\frac{1}{\mathrm{a}}$

(3) $\mathrm{e}={\mathrm{a}}^2$                    

(4) $\mathrm{a}={\mathrm{e}}^2$

Which of the following statements is wrong ?

(1) Rough surfaces are better radiators than smooth surface

(2) Highly polished mirror like surfaces are very good radiators

(3) Black surfaces are better absorbers than white ones

(4) Black surfaces are better radiators than white

Half part of ice block is covered with black cloth and rest half is covered with white cloth and then it is kept in sunlight. After some time clothes are removed to see the melted ice. Which of the following statements is correct ?

(1) Ice covered with white cloth will melt more

(2) Ice covered with black cloth will melt more

(3) Equal ice will melt under both clothes

(4) It will depend on the temperature of surroundings of ice

If between wavelength $\mathrm{\lambda }$ and $\mathrm{\lambda }+\mathrm{d\lambda }$, ${\mathrm{e}}_{\mathrm{\lambda }}$ and ${\mathrm{a}}_{\mathrm{\lambda }}$ be the emissive and absorptive powers of a body and ${\mathrm{E}}_{\mathrm{\lambda }}$ be the emissive power of a perfectly black body, then according to Kirchoff's law, which is true ?
(1) ${\mathrm{e}}_{\mathrm{\lambda }}$= ${\mathrm{a}}_{\mathrm{\lambda }}$= ${\mathrm{E}}_{\mathrm{\lambda }}$          

(2) ${\mathrm{e}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$=${\mathrm{a}}_{\mathrm{\lambda }}$

(3) ${\mathrm{e}}_{\mathrm{\lambda }}$= ${\mathrm{a}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$              

(4) ${\mathrm{e}}_{\mathrm{\lambda }}$${\mathrm{a}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$ = constant

When p calories of heat is given to a body, it absorbs q calories; then the absorbtion power of body will be ?
(1) p/q                         

(2) q/p

(3) ${\mathrm{p}}^2/{\mathrm{q}}^2$                     

(4) ${\mathrm{q}}^2/{\mathrm{p}}^2$

In rainy season, on a clear night the black seat of a bicycle becomes wet because -

1. It absorbs water vapour

2. Black seat is good absorber of heat

3. Black seat is good radiator of heat energy

4. None of the above