$A$ piece of iron is heated in a flame. It first becomes dull red, then becomes reddish yellow, and finally turns to white hot. The correct explanation for the above observation is possible by using

Two bodies $A$ and $B$ of equal surface area have thermal emissivities of $0.01$ and $0.81$ respectively. The two bodies are radiating energy at the same rate. Maximum energy is radiated from the two bodies $A$ and $B$ at wavelengths $\lambda_A$ and $\lambda_B$ respectively. The difference in these two wavelengths is $1 \mu m$. If the temperature of body $A$ is $5802 \ K$, then the value of $\lambda_B$ is:

$A$ black body has a maximum wavelength $\lambda_{m}$ at a temperature of $2000 \ K$. Its maximum wavelength at $3000 \ K$ will be:

The relation between the colour and the temperature of a star is given by

Observations of light from three different stars $A, B$,and $C$ show that the intensity of the red color is maximum for star $A$,the intensity of the blue color is maximum for star $B$,and the intensity of the yellow color is maximum for star $C$. Which of the following conclusions can be drawn from these observations?

The emissive power of a sphere of area $0.04 \,m^2$ is $0.7 \,kcal \,s^{-1} \,m^{-2}$. The amount of heat radiated in $20 \,s$ is: (in $\,kcal$)