(i) Define principal focus of a concave mirror.
(ii) Why do we prefer a convex mirror as a rear view mirror in vehicles?
(iii) We wish to obtain an erect image of an object using a convex lens. Draw a ray diagram to show the image formation in this case.
(i) Principal focus : A number of rays parallel to the principal axis, after reflection from a concave mirror, meet at a point on the principal axis which is called the principal focus.
(ii) Convex mirror always gives an erect though diminished- image. They have a wider field of view as they are curved outwards and hence the driver can view much larger area.
(iii) The diagram is as shown :
