Diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm

PHYSICS · Single correct · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments

Problem

Diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm. If speed of light in material of lens is

2 \times 10^8

m/s, the focal length of the lens is (1) 15 cm (2) 20 cm (3) 30 cm (4) 10 cm