The coefficient of linear expansion of brass and steel are ${\alpha }_1$ and ${\alpha }_2$. If we take a brass rod of length $l_1$ and steel rod of length $l_2$ at 0°C, their difference in length $\left(l_2-l_1\right)$ will remain the same at a temperature if

1. ${\alpha }_1{l}_2={\alpha }_2{l}_1$                                 

2. ${\alpha }_1{l}_2^2={\alpha }_2{l}_1^2$

3. ${\alpha }_1^2{l}_1={\alpha }_2^2{l}_2$                                   

4. ${\alpha }_1{l}_1={\alpha }_2{l}_2$

Heat travels through vacuum by 

1. Conduction                 

2. Convection

3. Radiation                     

4. Both (1) and (2)

We consider the radiation emitted by the human body. Which of the following statements is true?

(1) The radiation is emitted only during the day.

(2) The radiation is emitted during the summers and absorbed during the winters.

(3) The radiation emitted lies in the ultraviolet region and hence is not visible.

(4) The radiation emitted is in the infra-red region.

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 ?

1. ${\mathrm{\lambda }}_1$                     

2. ${\mathrm{\lambda }}_2$

3. ${\mathrm{\lambda }}_1$ and ${\mathrm{\lambda }}_2$         

4. ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2, {\mathrm{\lambda }}_3$ 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

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. ${\mathrm{q}}^2/{\mathrm{p}}^2$

There is a rough black spot on a polished metallic plate. It is heated upto 1400 K approximately and then at once taken in a dark room. Which of the following statements is true ?

1. In comparison with the plate, the spot will shine more

2. In camparison with the plate, the spot will appear more black

3. The spot and the plate will be equally bright

4. The plate and the black spot can not be seen in the dark room

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 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 that 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