The Earth radiates in the infra-red region of the spectrum. The spectrum is correctly given by

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 $\lambda_1/\lambda_2 =$

The maximum energy in thermal radiation from a source occurs at the wavelength $4000 \mathring A$. The effective temperature of the source is ....... $K$.

Ordinary bodies $P$ and $Q$ radiate maximum energy with a wavelength difference of $3 \mu m$. The absolute temperature of body $P$ is four times that of $Q$. The wavelength at which body $Q$ radiates maximum energy is (in $\mu m$)

According to Wien's displacement law:

If a black wire of platinum is heated, its colour first appears red, then yellow, and finally white. This can be understood on the basis of: