$A$ black body radiates maximum energy at wavelength $\lambda$ at temperature $T_1$ and its emissive power is $E$. When the temperature of the body is changed to $T_2$, it radiates maximum energy at wavelength $\frac{2\lambda}{3}$, then the emissive power will become

Heat loss takes place from a body maintained at a temperature of $400^{\circ} C$ to the surrounding air at $30^{\circ} C$ by convection and to the surrounding surfaces at $30^{\circ} C$ by radiation. The Newton's cooling coefficient is $20 \ W / m^2 \ K$ and the Stefan-Boltzmann constant is $5.67 \times 10^{-8} \ W / m^2 \ K^4$. If the rate of heat loss by convection is equal to the rate of heat loss by radiation, the emissivity of the body surface is

Which of the following statements is/are $CORRECT$?
$(i)$ $A$ body with large reflectivity is a poor emitter.
$(ii)$ $A$ brass tumbler feels much colder than a wooden tray on a chilly day.
$(iii)$ The Earth without its atmosphere would be inhospitably cold.
$(iv)$ Heating systems based on the circulation of steam are more efficient in warming a building than those based on the circulation of hot water.

$A$ wall with a cavity consists of two layers of brick separated by a layer of air. All three layers have the same thickness,and the thermal conductivity of the brick is much greater than that of air. The left layer is at a higher temperature than the right layer,and a steady-state condition exists. Which of the following graphs correctly predicts the variation of temperature $T$ with distance $d$ inside the cavity?

$A$ black body radiates maximum energy at wavelength $\lambda$ and its emissive power is $E$. Now, due to a change in the temperature of that body, it radiates maximum energy at wavelength $\frac{2 \lambda}{3}$. At that temperature, the emissive power is:

Three rods of Copper,Brass,and Steel are welded together to form a $Y$ shaped structure. The area of cross-section of each rod is $4 \ cm^2$. The end of the copper rod is maintained at $100^\circ C$,whereas the ends of the brass and steel rods are kept at $0^\circ C$. The lengths of the copper,brass,and steel rods are $46 \ cm$,$13 \ cm$,and $12 \ cm$ respectively. The rods are thermally insulated from the surroundings except at the ends. The thermal conductivities of copper,brass,and steel are $0.92$,$0.26$,and $0.12 \ CGS$ units respectively. The rate of heat flow through the copper rod is ....... $cal \ s^{-1}$.