Two identical concex 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 on lens`L_(1)`on the common axis of two lenses.Find where a convex mirror of radius of curvature`5cm`should be placed so that the final image coincides with the object.?

Answer

`5.9cm,10.9cm`

Explanation

Taking refraction from first lens
`(1)/(v)-(1)/(u)=(1)/(f)`
`(1)/(v)-(1)/(-20)=(1)/(15)rArr v=60cm`
taking refraction from second lens
`(1)/(v')-(1)/(40)=(1)/(15)rArr v'=(120)/(11)cm rArr v'=10.9cm`
for ray to retrace path ray should be incident either to wards towards at pole or at C.

`5.9cm,10.9cm`