Question

Two identical bi-convex lenses L1 and L2 are arranged 10 cm apart. A collimated, parallel beam of light strikes L1 from the left and converges 4.3 cm from the left lens. The emergent rays on the right of L2 will be:

(a) Diverging
(b) Parallel
(c) Converging
(d) No change

Answer 1

The emergent rays on the right of the second bi-convex lens (L2) in the described setup will be (c) converging because the light that passes through the first lens and converges before reaching the second lens will be further converged by the second lens.

Step-by-step explanation:

In this scenario, we have two identical bi-convex lenses placed 10 cm apart, and we know that after passing through the first lens (L1), a collimated beam of light converges at a point 4.3 cm from the left lens.

Since the lenses are identical and the distance at which the light converges after the first lens (4.3 cm) is less than the separation between the two lenses (10 cm), the focal point of the first lens lays between the two lenses.

Therefore, when the converging beams from L1 enter the second lens (L2), they will still be convergent, and not yet parallel or divergent. L2 will further converge the rays, and as a result, the emergent rays on the right of L2 will continue to be converging.