One face of an equiconvex lens of focal length 60cm made of glass `(mu=1.5)` is silvered. Does it behave like a convex mirror or concave mirror? Determine its focal length.

Explanation

Using lensmaker's formula, we know that, for a glass made of glass `(mu=1.5)`, the focal length of an equiconvex lens is equal to its radius of curvature.
`(1)/(f)=(1.5-1)((2)/R)rArr f=R`
For a lens-mirror combination, we have `(1)/(F) =(2)/(f_(f))+(1)/(f_(m))`
Here `f_(f)=+60cm` (converging ) and
`f_(m)=(+R)/(2)=+30` (converging)
`:. (1)/(F)=(2)/(60)+(1)/(30)=(1)/(15)` or `F=+15 cm`.
The positibe sign indicates that the resulting mirror is converging or concave.