NEET Physics Lenses MCQ Question
Two thin lenses, one convex with focal length 30 cm and one concave with focal length 20 cm, are placed in contact. What is the effective focal length of the combination?
60 cm (diverging)
10 cm (converging)
-60 cm (diverging)
12 cm (converging)
Correct Answer
Detailed Explanation
Using the formula for lenses in contact, 1/F = 1/f1 + 1/f2. The focal lengths are 30 cm (positive) and -20 cm (negative), giving 1/F = 1/30 - 1/20 = -1/60, so F = -60 cm, indicating a diverging lens.
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