A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance :

1. 37.3 cm

2. 46.0 cm

3. 50.0 cm

4. 54.0 cm

Doubtly Asked 30 Oct 2026 NEET UG 2016 Phase 1 Practice test neet Save WhatsApp Report

1 answer

Best answer

Answer: 4. 54.0 cm

Key idea: the objective forms an image of the nearby object; the eyepiece must focus on that image (final image at infinity).

Objective: \(\dfrac1v=\dfrac1{40}-\dfrac1{200}=\dfrac{4}{200}\Rightarrow v_o=50\) cm.
Eyepiece gives parallel rays when the image lies at its focus: \(u_e=4\) cm.
Separation \(=50+4=54\) cm.

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

Was this answer helpful?