Wien's Displacement Law

Q.

If black wire of platinum is heated, then its colour first appear red, then yellow and finally white. It can be understood on the basis of

1. Wien's displacement law

2. Newton's law of cooling

3. None of the above

4. Prevost theroy of heat exchange

Q. The energy radiated by a black body at $2300\text{K}$ is found to have maximum intensity at wavelength $1260\text{nm}$, its emissive power being $8000{\text{W/m}}^2$. When the body is cooled to a temperature $T\text{K}$, the emissive power is found to decrease to $500{\text{W/m}}^2$. Find the wavelength at which intensity of emission is maximum at the temperature $T$.

1. $1575\text{nm}$
2. $2520\text{nm}$
3. $1260\text{nm}$
4. $5040\text{nm}$

Q. The intensity of radiation emitted by the sun has its maximum value at a wavelength $510\text{nm}$ and that emitted by another star has the maximum value at $350\text{nm}$. If we treat them as black bodies, then the ratio of the surface temperature of the sun and the star is

1. $0.69$
2. $1.46$
3. $1.21$
4. $0.83$

Q.

explain how the air in contact with the warm ground is heated by conduction?

Q. The power radiated by a black body is $P$ and it radiates maximum energy around wavelength ${\lambda }_{\circ }$. If the temperature of the black body is now changed so that it radiates maximum energy around a wavelength $3{\lambda }_{\circ }/4$, the power radiated by it will increase by a factor of

1. $\frac{4}{3}$
2. 
   $\frac{16}{9}$
3. 
   $\frac{64}{27}$
4. $\frac{256}{81}$

Q.

The energy spectrum of a blackbody exhibits a maximum around a wavelength ${\lambda }_0$. The temperature of the black body is now changed such that the energy is maximum around a wavelength $\frac{3{\lambda }_0}{4}$ The power radiated by the blackbody will now increase by a factor:

1. $\frac{256}{81}$

2. $\frac{16}{9}$

3. $\frac{4}{3}$

4. None

Q.

Which of the given phenomena is not related to convection?

1. Maintaining comfortable room temperature in cold countries

2. Formation of land and sea breezes

3. Formation of trade winds

4. In winter metallic handles appear colder than wooden door

Q. The adjoining diagram shows the spectral energy density distribution $E_{\lambda }$ of a black body at two different temperatures. If the areas under the curves are in the ratio $16:1$, the value of temperature $T$ is

1. $32000\text{K}$
2. $16000\text{K}$
3. $8000\text{K}$
4. $4000\text{K}$

Q.

Two bodies A and B have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of the two bodies are the same . The two bodies emit total radiant power at the same rate. The wavelength ${\lambda }_B$ corresponding to maximum spectral radiancy in the radiation from B shifted from the wavelength corresponding to maximum spectral radiancy in the radiation from A, by 1.00 $\mu m$. If the temperature of A is 5802 K

1. the temperature of B is 1934 K

2. ${\lambda }_B=1.5\mu m$

3. the temperature of B is 11604 K

4. the temperature of B is 2901 K