The concave and convex surface of a thin concavo-convex lens of refractive index 1.5 has radius of curvature 50 cm and 10 cm respectively. The concave side is slivered then if the equivalent focal length of the silvered lends is `-5x`cm then find x.

Answer

5

Explanation

lens `(1)/(f_(L))=(mu-1)[(1)/(R_(1))-(1)/(R_(2))]`
`(1)/(f_(L))=(1)/(25)`
mirror `(1)/(f_(M))=(1)/(25)`
Equivalent focal length
`(1)/(f_(eq))=(1)/(f_(M))-(2)/(f_(L))`
`f_(eq)=25cm`