A 1100 W light bulb is placed at the centre of a spherical chamber of radius 20 cm. Assume that, 60% the energy supplied to the bulb is converted into light and that the surface of the chamber is perfectly absorbing. The force and pressure exerted by the light on the surface of chamber is

Consider a spherical chamber of radius 20 cm.  Bulb is placed at point S as shown in figure.
Intensity of light at surface,

$I=\frac{0.6P}{4\pi r^2}$        

For perfectly absorbing surface, force exerted on the surface,  $F=\frac{0.6 P}{c}$   [where P is power of bulb]

$\therefore$    $F=\frac{0.6\times 1100}{3\times {10}^8}=2.2\times {10}^{-6} \mathrm{N}$

Pressure exerted by light =  $\frac{I}{c}=\frac{0.6P}{4\pi r^{2}c}=\frac{0.6\times 1100}{4\pi (0.2{)}^2\times 3\times {10}^8}$

$=4.4\times {10}^{-6} \raisebox{1ex}{$N$}\!\left/ \!\raisebox{-1ex}{$m^2$}\right.$