Question

The radius of curvature of the convex surface of a planoconvex lens is 10 cm. What is the focal length of the planoconvex 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.