Question

The radius of curvature of the convex surface of a planoconvexlens is 10 cm. What is the focal length of the plano-convex lens? (Here $\mu$ = 1.5)

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

Answer 1

The correct option is B 20 cm

focal length $f=?$ ;radius of curvature $R=10cm$

As $\frac{1}{f}=\frac{(\mu -1)}{R}$

$f=\frac{R}{\mu -1}=\frac{10}{1.5-1}=20cm$

hence, the focal length of the plano-convex lens is 20cm.