A point source of light emits isotropically with a power of

A point source of light emits isotropically with a power of 208 W. What is the force due to the light on a totally absorbing sphere of radius 2.6 cm at a distance of 30 m from the source?

Solution

I = = 208 / 4 pi * 30² = 0.0184 W/m²

P = F / A, F = P A, F = I A / c

F = 0.0184 * pi * 0.026² / (3 * 10⁸)

= 1.3 * 10^-13 N