NEET Physics Lenses MCQ Question
If a convex lens of focal length 30 cm is placed in contact with a concave lens of focal length 20 cm, what is the effective focal length of the lens system?
+60 cm
-60 cm
+12 cm
-12 cm
Correct Answer
Detailed Explanation
For two lenses in contact, the effective focal length is given by 1/f = 1/f1 + 1/f2. Here, f1 = +30 cm (convex) and f2 = -20 cm (concave). So, 1/f = 1/30 - 1/20, giving f = -60 cm.
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