Assuming the sun to be a spherical body of radius R at a temperature of T K, evaluate the total radiant power, incident on earth, at a distance r from the sun:

Radius of earth is $r_0$ .

• A

  $\frac{{\mathrm{r}}_0^2{\mathrm{R}}^2{\mathrm{\sigma T}}^4}{4{\mathrm{\pi r}}^2}$

• B

  $\frac{{\mathrm{R}}^2{\mathrm{\sigma T}}^4}{{\mathrm{r}}^2}$

• C

  $\frac{4{\mathrm{\pi r}}_0^2{\mathrm{R}}^2{\mathrm{\sigma T}}^4}{{\mathrm{r}}^2}$

• D

  $\frac{{\mathrm{\pi r}}_0^2{\mathrm{R}}^2{\mathrm{\sigma T}}^4}{{\mathrm{r}}^2}$