The following figure represents two biconvex lenses $\mathrm{L}_{1}$ and $\mathrm{L}_{2}$ having focal length 10 cm and 15 cm respectively. The distance between $\mathrm{L}_{1}$ \& $\mathrm{L}_{2}$ is :

JEE Main · 2024 · 09 Apr 2024 · Shift 2 · Geometrical Optics

The following figure represents two biconvex lenses

L_{1}

and

L_{2}

having focal length 10 cm and 15 cm respectively. The distance between

L_{1}

L_{2}

is :

(A)10 cm
(B)15 cm
(C)25 cm✓ Correct
(D)35 cm

Answer: (C)

Solution

Parallel rays incident on

L_{1}

(focal length 10 cm) converge to its focus, and for the emergent rays from

L_{2}

to become parallel again, that focus must coincide with the focus of

L_{2}

(focal length 15 cm) on the same side. Hence the two lenses must be separated by the sum of their focal lengths:

d = f_{1} + f_{2} = 10 + 15 = 25 cm

JEE Main · 2024 · 09 Apr 2024 · Shift 2 · Single correct option

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