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In normal adjustment, for a refracting telescope, the distance between objective and eye-piece is 30 cm. The focal length of the objective, when the angular magnification of the telescope is 2, will be

Asked in JEE Main 28th July 1st Shift 2022 · Telescopes

Answer: (1) 20 cm

Step-by-step solution

Normal adjustment: fₒ + fₑ = 30 cm and (fₒ)/(fₑ) = 2

3fₑ = 30, so fₑ = 10 cm

fₒ = 20 cm

Why the other options are wrong

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