Find the distance of the image from object O, formed by the… | JEE Main 2021 (27 Aug, Shift 1)

Q48JEE Main 2021 · 27 AUG · SHIFT 1Difficult

Combination of Lenses

Find the distance of the image from object O, formed by the combination of lenses in the figure:

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Answer: (a)

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 $u = +10$ , $f = -10$ ): $\frac{1}{v_2} = 0$ , so the beam becomes parallel.
Lens 3 ( $f = 30$ ) forms the image 30 cm to its right.
Distance from O: $30 + 5 + 10 + 30 = 75\text{ cm}$ .
So the answer is (a) 75 cm.

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