Question

A parallel beam of rays is incident on a convergent lens with a focal length of 40cm where should a divergent lens with focal length of 15cm be placed for the beam of rays to remain parallel after passing through the two lenses ? Draw a ray diagram

Answer 1

Explanation:

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Answer 2

Answer:

When parallel beams of light are incident on the convex lens then after refraction the beams will converge at the focal point of the lens. We have to find the position of diverging lens so the beams after refracting from lens emerge as a parallel beam. The effective focal length of the lens must be infinity as the rays are parallel.

Using the formula:

F = effective focal length = ∞

f1 = focal length of converging lens = 40 cm

f2 = focal length of diverging lens = -15 cm

a = distance between two lenses = ?

So the distance between two lens should be 25 cm so as to get parallel beams of light after refraction.