An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of

1. small focal length and large diameter

2. large focal length and large diameter

3. large focal length and small diameter

4. small focal length and small diameter

Doubtly Asked 30 Oct 2026 NEET UG 2018 neet Save WhatsApp Report

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Answer: 2. large focal length and large diameter

Angular magnification of an astronomical telescope is \(m=\dfrac{f_o}{f_e}\), so a large objective focal length gives a large magnification.

Resolving power is \(\propto \dfrac{D}{1.22\lambda}\), so high resolution needs a large objective diameter.

Hence the objective should have a large focal length and a large diameter (option 2).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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