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Physics · PYQ NEET UG 2023
हिन्दीTwo thin lenses are of same focal lengths (\( f \)), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be :
Correct answer · Option 1
Infinite
Explanation
For two thin lenses in contact, \( \frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2} \). Since one is convex (\( +f \)) and the other is concave (\( -f \)), \( \frac{1}{F} = \frac{1}{f} - \frac{1}{f} = 0 \), which gives \( F = \infty \).
