Question

A plano convex lens of $(f=20cm)$ is silvered at plane surface. New $f$ will be

• A. $20cm$
• B. $40cm$
• C. $30cm$
• D. $10cm$

Answer 1

Answer: (D)

$\frac{1}{F}=\frac{2}{f_1}+\frac{1}{f_m}\Rightarrow \frac{1}{F}=\frac{2}{20}+\frac{1}{\infty }\Rightarrow F=10cm$