The radius of curvature of the convex surface of a thin plano-convex lens is 12 cm, and the refractive index of its material is 1.6. What is the power of lens ?

Explanation

Such lens acts as a concave mirror of focal length f given by `1/f=2/(f_(1))+1/(f_(m))`.
Here `1/(f_(1))=(mu-1)/R`
= `(1.5-1)/(12cm)=1/(24cm)=1/(24cm)`
and `1/(f_(m))=1/oo=0`
`therefore1/f=2xx1/(24cm)=1/(12cm)`
or f = 12 cm
`therefore` Parallel rays will converge at 12 cm from the lens