NEET2021Physics-Optics
NEET 2021 Physics Lens Combination MCQ Question
Type: MCQ-conceptual-Medium-Class 12
A convex lens ‘A’ of focal length 20 cm and a concave lens ‘B’ of focal length 5 cm are kept along the same axis with a distance ‘d’ between them. If a parallel beam of light falling on ‘A’ leaves ‘B’ as a parallel beam, then the distance ‘d’ in cm will be :
A
25
B
15
C
50
D
30
Correct Answer
Option B
Detailed Explanation
For the system to behave as a parallel beam, the effective focal length should be infinite. Using the lens formula for combination, 1/f = 1/f1 + 1/f²⁻ d/(f1*f2), solve for d.
Found an issue with this question?