Rate of heat flow through a cylindrical rod is $H_1$. Temperatures of ends of rod are $T_1$ and $T_2$. If all the dimensions of rod become double and temperature difference remains same and rate of heat flow becomes $H_2$. Then,

A ring consisting of two parts $ADB$ and $ACB$ of same conductivity $K$ carries an amount of heat $H$. The $ADB$ part is now replaced with another metal keeping the temperatures $T_1$ and $T_2$ constant. The heat carried increases to $2 \mathrm{H}$. What should be the conductivity of the new $ADB$ part? $($Given $,\frac{ACB}{ADB}=3)$.

The graph, shown in the below diagram, represents the variation of temperature $\left(T\right)$ of two bodies, $x$ and $y$ having same surface area, with time$\left(t\right)$ due to the emission of radiation. Find the correct relation between the emissivity $\left(e\right)$ and absorptivity $\left(a\right)$ of two bodies

Assertion: A body that is a good radiator is also a good absorber of radiation at a given wavelength.

Reason: According to Kirchhoff's law, the absorptivity of a body is equal to its emissivity at a given wavelength.