Question

Two identical convex lenses $L_1$ and $L_2$ are placed at a distance of $20cm$ from each other on the common principal axis. The focal length of each lens is $15cm$ and the lens $L_2$ is to the right of lens $A$.A point object is placed at a distance of $20cm$ on the left of lens $L_1$, on the common axis of two lenses. Find, where a convex mirror of radius of curvature $5cm$ should be placed to the right of $L_2$ so that the final image coincides with the object?

Answer 1

The distance $=20cm$

Focal lengths of each lense$-15cm$

The lens $l_2$ to the right of lens A

A point object is placed at a distance of $=20cm$ left of lose $l_1$

$r=5cm$

Image after 1^st refraction from lens

$\frac{1}{v}-\frac{1}{(-20)}=\frac{1}{15}v=60cm$

After reflection from the mirror,

$v^{\prime }=-60cm$

It will refract again by the curved surface

$\frac{1}{v^{”}}-\frac{1}{60}=\frac{1}{15}\frac{1}{v^{”}}=12cm12cmleft$