The position of the image formed by the combination of lenses is: (a) 15 cm (right of second lens) (b) 30 cm (right of third lens) (c) 30 cm (left of third lens) (d) 15 cm (left of second lens)

Answer: (b). Lens 1: 1/v₁ = 1/10 - 1/30 ⇒ v₁ = 15 cm, i.e. 10 cm beyond lens 2. Lens 2 (virtual object u = +10): 1/v₂ = -1/10 + 1/10 = 0 ⇒ parallel beam. Lens 3 focuses the parallel beam at its focus: 30 cm to its right. So the answer is (b) 30 cm right of third lens.

The position of the image formed by the combination of lenses is: | JEE Main 2024 (8 Apr, Shift 2)

Q30JEE Main 2024 · 8 APR · SHIFT 2Difficult

Combination of Lenses

The position of the image formed by the combination of lenses is:

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Answer: (b)

Lens 1: $\frac{1}{v_1} = \frac{1}{10} - \frac{1}{30} \Rightarrow v_1 = 15\text{ cm}$ , i.e. 10 cm beyond lens 2.
Lens 2 (virtual object $u = +10$ ): $\frac{1}{v_2} = -\frac{1}{10} + \frac{1}{10} = 0 \Rightarrow$ parallel beam.
Lens 3 focuses the parallel beam at its focus: 30 cm to its right.
So the answer is (b) 30 cm right of third lens.

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