Question

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

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

Answer 1

The correct option is B $20cm$

$R=10cm;f=?$

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

$\frac{1}{f}=(1.5-1)\left(\frac{1}{10}\right)$

$f=\frac{1}{0.05}=20cm$

hence,option B is correct.