Question

A double convex thin lens made of glass (refractive index 1.5) has both radii of curvature of magnitude 20 cm. Incident light rays parallel to the axis of the lens will converge at distance L such that

• A. L = 20 cm
• B. L = 10 cm
• C. L = 40 cm
• D. L = 20/3 cm

Answer 1

The correct option is A L = 20 cm

We know that,
$\frac{1}{f}=(\mu -1).\frac{2}{R}$
Placing R = 20 cm and refractive index as 1.5, we will get the distance as 20 cm.