Question

A biconvex thin lens is prepared from glass (u=1.5 ), the two bounding surface having equal radii of 25 cm each. One of the surface is silvered from outsides to make reflecting . Where should an object be place before the lens so that the image is formed on the object itself?

Answer 1

The power of the lens (P) G given by lens maker's formula.

$P=(\mu-1)\left(\dfrac{1}{R_1}-\dfrac{1}{R_2}\right)$

where $R_1=-R_2=25cm$

$=(1.5-1)(\frac{1}{25}-\left(\frac{1}{-25}\right))$

$=0.5\times \frac{2}{25}=\frac{1}{25}c{m}^{-1}$

when its surface is served it acts as a concave