Question

A metallic sphere of radius 21 cm is kept in the path of a parallel beam of light of intensity Wm 2. The force exerted by beam on the sphere is 7nx 10-13 N. Find n.

Answer 1

Explanation:

Radius of the sphere, r = 1 cm

Intensity of light, I = 0.5 Wcm-²

Let A be the effective area of the sphere perpendicular to the light beam.

So, force exerted by the light beam on the sphere is given by,

F = P/c = (Al)/c

`F = (pi xx (1)^2 xx 0.5)/(3 xx 10^8)`

`= (3.14 xx 0.5)/(3 xx 10^8)`

= 0.523 xx 10^-8`

= 5.2 xx 10^-9 "N"