Question

A point source S is placed at a distance of 15 cm from a converging lens of focal length 10 cm on its.
principal axis. A diverging mirror of focal length 12 cm is placed so that a real image is formed on the
source itself. Determine the distance between lens and mirror in cm.
​

Answer 1

Explanation:

Formula for refraction through the lens is,

u=−15cm and f=±10cm

v

1

+

15

1

=

10

1

v=30cm

As v is positive,the image I

1

,is formed to the right of lens.

The convex mirror is to be placed to the right of lens in such a way hat light rays fall on the mirror normally.

Then only the light rays will retrace their path and form final image on the object itself.

This shows that image I

1

formed by the lens should be at the center of curvature of the mirror i.e,PI

1

=R=2f=24cm

As ∣v∣=OI

1

=30cm. ,Hence OP=30−24=6cm

Thus,the convex mirror should be placed at a distance of 6cm to the right of lens