Rays Not Parallel To Principle Axis

A point object is placed on the principle axis of a converging lens of focal length 5cm at a distance of 30cm form it. A glass plate (mu = 1.50) of thickness 3cm is placed on the other side of the lens, comes out parallel to the principle axis?

Rays parallel to principal axis, incident on the spherical mirror at different heights from principal axis are focused at different points. And due to this reason we cannot define unique focus. This is known as spherical aberration. Angle of incidence theta shown in figure depends on the height of ray above principal axis. Focal length of spherical mirror can be easily written in terms of angle theta shown in figure as follows : f = R- (R)/(2)sec theta Here R is radius of curvature of mirror. The light rays which are very close to principal axis are known as paraxial rays and rays far away from principal axis are called marginal rays. Let f_(P) and fm represent the focal length corresponding to paraxial rays and marginal rays respectively then

Assertion:- Paraxial rays are always parallel to the principal axis. Reason:- A parallel beam parallel to principal axis converges at the focal point.

Radius of curvature of concave mirror is R and a light ray is incident on it parallel to principal axis at a height h above the principal axis. Calculate distance of the point from pole of mirror where reflected ray intersects with principal axis.

The value of the of d_(1) and d_(2) for final rays to be parallel to the principle axis are (focal lengths of the lenses are written on the lenses).

Parallel rays