The colour of a star is an indication of its

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 $\,kcal$)

The wavelength of maximum intensity of radiation emitted by a star is $289.8 \, nm$. The radiation intensity of the star is (Stefan's constant $\sigma = 5.67 \times 10^{-8} \, W m^{-2} K^{-4}$, Wien's constant $b = 2898 \, \mu m K$).

The wavelength of maximum emitted energy $(\lambda_m)$ of a body at $700 \ K$ is $4.08 \ \mu m$. If the temperature of the body is raised to $1400 \ K$,then the value of $\lambda_m$ will be (in $\mu m$)

The spectral emissive power $E_\lambda$ for a body at temperature $T_1$ is plotted against the wavelength and the area under the curve is found to be $A$. At a different temperature $T_2$,the area is found to be $9A$. Then $\lambda_1/\lambda_2 =$

When an iron rod is heated, the variation of colour from dull red to white can be explained by