A flat circular mirror of radius 0.170 m is lying on the floor. Centered directly above the mirror, at a height of 0.720 m, is a small light source. Calculate the diameter of the bright circular spot formed on the 2.80 m high ceiling by the light reflected from the mirror.

Explanation:

The light coming from source will be falling on the periphery of the mirror at an angle of θ where

tanθ = .17 / .72

= 17 / 72

angle of reflection will also be θ . The reflected light will fall on the ceiling at a distance d from a point just above the point where the incident light falls .

d / 2.8 = tanθ

d = 2.8 x 17 / 72

= .66 m

radius of the circular spot on the ceiling

= .66 + .17

= .83 m

diameter = 2 x .83

= 1.66 m