A perfectly reflecting solid sphere of radius r is kept in the path of a parallel beam of light of large aperture . If the beam carries an intensity I find force exerted by beam on sphere .

Question

$(a)\;\large\frac{\pi r^2 I}{C}\qquad(b)\;\large\frac{\pi r^2 I}{2C}\qquad(c)\;\large\frac{\pi r^2 I}{3C}\qquad(d)\;\large\frac{4}{3}\;\large\frac{\pi r^2 I}{C}$