Physics-Lenses
NEET Physics Lenses MCQ Question
Type: MCQ-numerical-Easy-Class 12
If two thin lenses, one convex with a focal length of 30 cm and one concave with a focal length of 20 cm, are placed in contact, what is the effective focal length of the lens system?
A
60 cm
B
-60 cm
C
12 cm
D
-12 cm
Correct Answer
Option D
Detailed Explanation
Using the formula for lenses in contact, 1/f = 1/f1 + 1/f2, where f1 = 30 cm and f2 = -20 cm (negative for concave), the effective focal length is computed as -12 cm.
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