Question

A convergent beam of light passes through a diverging lens of focal length 0.2 m and comes to focus 0.3 m behind the lens. Find the position of the point at which the beam would converge in the absence of lens.

• A. 0.22 m
• B. 0.1 m
• C. 0.2 m
• D. 0.12 m

Answer 1

The correct option is D

0.12 m

OP can be taken as the virtual object for the lens whose image is formed at I

Here, f = -0.2m = -20cm

v = 0.3 m = 30 cm

We know that, 1/u = 1/v - 1/f = 1/30 + 1/20

or, 1/u = 50/600

or, u = 12 cm = 0.12m

Thus, if the lens was not there, the rays would have met at a distance 12 cm behind the lens.