1
Tip 1
In problems involving a combination of lenses, always concentrate on one lens at a time.
In problems involving a combination of lenses, always concentrate on one lens at a time.
- For convenience, mark the crucial points such as f, 2f, R on the principal axis.
- Start from the object, the direction of rays going towards the lens is taken to be positive.


- We repeat the above procedure until no further images can be formed.
NOTE: The same tips are helpful while deriving the lens maker's formula as well as understanding the optical instruments like compound microscope and refracting telescopes.
Let us solve some sample questions: A luminous object is placed at a distance of 30 cm from the convex lens of focal length 20 cm.The distance from the lens a convex mirror of radius of curvature 10 cm should be placed on the other side of the lens such that the real images formed on the source itself is
What should be the value of distance d so that final image is formed on the object itself. (focal lengths of the lenses are written on the lenses).