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Question: Answered & Verified by Expert
A thin convex lens of focal length $10 \mathrm{~cm}$ is placed in contact with a concave lens of same material and of same focal length. The focal length of combination will be
PhysicsRay OpticsJEE Main
Options:
  • A Zero
  • B Infinity
  • C 10 cm
  • D 20 cm
Solution:
2035 Upvotes Verified Answer
The correct answer is: Infinity
$f=\frac{f_1 f_2}{f_1+f_2}=\frac{10(-10)}{10+(-10)}=\frac{-100}{10-10}={ }_{\infty}$

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