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MHT CET 2020 (16 Oct, Shift 2) · Optical Instruments & the Eye

Optical Instruments & the Eye question from MHT CET 2020 (16 Oct, Shift 2)

Q34MHT CET 2020 · 16 OCT · SHIFT 2Medium

Optical Instruments & the Eye

There are four convex lenses $L_1, L_2, L_3$ and $L_4$ of focal length $2, 4, 6$ and 8 cm, respectively. Two of these lenses from a telescope of length 10 cm and magnifying power 4. The objective and eye lenses are respectively

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Answer: (d)

Normal adjustment: $f_o + f_e = 10$ cm and $\dfrac{f_o}{f_e} = 4$ .
$5f_e = 10 \Rightarrow f_e = 2$ cm, $f_o = 8$ cm.
Objective is $L_4$ (8 cm), eyepiece is $L_1$ (2 cm).
So the answer is (d) $L_4, L_1$ .

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