JEE Main & Advanced
Physics
Ray Optics
Question Bank
Critical Thinking
question_answer
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 the distance d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then distance d in cm will be [MNR 1990; IIT-JEE 1985]
A) 25
B) 15
C) 30
D) 50
Correct Answer:
B
Solution :
From figure it is clear that separation between lenses \[d=20-5=15\,cm\]