Find the distance CQ if incident light ray parallel to principal axis is incident at an angle i. Also, find the distance CQ if `irarr0` .

Explanation

`cos I = R/(2CQ)`
`rArr CQ=R/(2 cos i)`
As i increases cos i decreases.
Hence CQ increases
So, paraxial rays meet at a distance equal to R/2 from centre of curvature, which is called focus, Principal focus (F) is the point of intersection all the reflected rays for which the incident rays strike the mirror (with small aperture) parallel to the principal axis. In concave mirror it is real and in the convex mirror it is virtual. The distance from pole to focus is called focal length. Aperture (related to the size of mirror) is the diameter of the mirror.