Question

In a plano convex lens the radius of curvature of the convex lens is $10cm$. If the plane side is polished, then the focal length will be
(Refractive index $=1.5$)

• A. $20cm$
• B. $10cm$
• C. $15cm$
• D. $5cm$

Answer 1

The correct option is B $10cm$

The plane surface is polished,

So, $f_2=\infty$

$\frac{1}{f_1}=(\mu -1)(\frac{1}{R_1}-\frac{1}{\infty })$

$\frac{1}{f_1}=\left(\frac{1.5-1}{R_1}\right)$

Given, $R_1$= 10 cm

$\frac{1}{F}=\frac{2\times 0.5}{10}$

$F=10cm$