G L Mittal and TARUN MITTAL Solutions for Chapter: Thermal Radiation, Exercise 3: FOR DIFFERENT COMPETITIVE EXAMINATIONS

Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. The first and third plates are maintained at temperatures 2T and 3T respectively. The temperature of the middle (i.e. second) plate under steady state condition is

If a piece of metal is heated to temperature θ and then allowed to cool in a room which is at temperature $T_0$ the graph between the temperature T of the metal and time $t$ will be closed to:

Certain quantity of water cools from $70°C$ to $60°C$ in the first $5$ minutes and to $54°\mathrm{C}$ in the next 5 minutes. The temperature of the surrounding is

Three disc A, B and C having radii $2\mathrm{m}, 4\mathrm{m} \mathrm{and} 6 \mathrm{m}$ respectively are rotated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are $300\mathrm{nm}, 400\mathrm{nm}, \mathrm{and} 600 \mathrm{nm}$ respectively. The power radiated by them are $\mathrm{Qa} ,{\mathrm{Q}}_{\mathrm{b}} \mathrm{and} {\mathrm{Q}}_{\mathrm{c}}$ respectively.

A liquid in a beaker has temperature $\theta$ at time $t$ and ${\theta }_0$ is temperature of surroundings, then according to Newton's law of cooling, correct graph between $\log (\mathrm{\theta } -{\mathrm{\theta }}_0) \mathrm{and} \mathrm{t}$ is:

Two bodies A and B have the same outer surface areas, have thermal emissivities of $0.01$ and $0.81$ respectively. They radiate total radiant energy at the same rate The wave length ${\mathrm{\lambda }}_{\mathrm{B}}$ corresponding to the maximum radiant energy from B is displaced from the wavelength corresponding to the maximum spectral radiancy of A by $1 \mathrm{\mu m}$. If, the temperature of A is $5802 \mathrm{K}$, then,

On investigation of light from three different stars $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$, it was found that in the spectrum of $\mathrm{A}$ the intensity of red colour is maximum, in $\mathrm{B}$ the intensity of blue colour is maximum and in $\mathrm{C}$ the intensity of yellow colour is maximum. From these observations it can be concluded that

An ideal black body at room temperature is thrown in a furnace. It is observed that