A ray of light is incident on a concave mirror . It is parallel to the principal axis and its height from principal axis is equal to the focal length of the mirror. The ratio of the distance of point B to the distance of the focus from the centre of curvature is (AB is the reflected ray)

Options

A. `(2)/(sqrt(3))`
B. `(sqrt(3))/(2)`
C. `(2)/(3)`
D. `(1)/(2)`

Answer

A

Explanation

In `triangle ACD :"sin"theta= (f)/(2f) implies theta= 30^(@)`
`PB = R-(R)/(2)"sec"theta = R - (R)/(sqrt(3))`
PC = R implies CB = PC- PB = R-R + (R)/(sqrt(3))`
=`(R)/(sqrt(3)) = (2f)/(sqrt(3)) therefore (CB)/(f) = (2)/(sqrt(3))`