A blackened metal foil receives heat from a heated sphere placed at a distance $r$ from it. It is found that the foil receives power $P$. If the temperature and the distance of the sphere are doubled, then, the power received by the foil will be,

The temperature of the two outer surfaces of a composite slab consisting of two materials having thermal conductivities as $K$ and $2K$ of thickness $x$ and $4x$ respectively are $T_2$ and $T_1\left(T_2>T_1\right)$. The rate of heat transfer through the slab in a steady state is $\left(\frac{A\left(T_2-T_1\right)K}{x}\right)f$ with $f$ equal to

Assertion : If temperature of any Ideal Black Body is increased by $100\%$ then, there will be $400\%$ increment in the quantity of radiation emitted from its surface.

Reason : The equation $\frac{\mathrm{\Delta }E}{E}=4\frac{\mathrm{\Delta }T}{T}$ is also true for large percentage increase $\left(E=\sigma T^4\right)$

Assertion : Wien's displacement law fails for short wavelengths.

Reason : Intensity of radiations of very short wavelength is large.

Assertion : In conduction mode of transmission of heat, transfer of heat is due to the interatomic collisions without the actual movement of atoms.

Reason: Steady state during conduction of heat through a rod means temperature gradient of all parts of the rod is same.

Assertion : In a room containing air, heat can go from one place to another by radiation only.

Reason : In conduction and convection, heat is transferred from one place to other by actual motion of heated material.

Assertion : Radiation is the fastest mode of heat transfer.

Reason : The nature of emitted radiations from ideal black body depends only on its temperature.

Assertion : Heat radiation are always obtained in infrared region of electromagnetic wave spectrum.

Reason : Complementary colour are those two colour present in the spectrum which when mixed produce white light.