Question

A plano convex lens( μ=1.5) with radius of curvature 20 cm is silvered at the curved surface. The power of the system is..?

Answer 1

Answer:-

Given

$\mu =1.5 \ \ , R_1=\infin \ \ \ , \\R_2=-20cm (the \ object \ lies \ on \ the \ plane \ side)$

we know that

$\frac{1}{f}=(\mu-1)(\frac{1}{R_1}-\frac{1}{R_2})$

putting the values

$\frac{1}{f}=(1.5-1)(\frac{1}{\infin}-\frac{1}{-20})$

$\frac{1}{f}=\frac{1}{40}\\ \boxed{f=40 cm}$

$D=\frac{1}{40cm}$ [1 meter=100cm]

$D=\frac{100}{40}$

$\boxed{power=2.5 \ D}$