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Question: Answered & Verified by Expert

Two plano-convex lenses of focal lengths 20 cm and 30 cm are placed together to form a double convex lens. The final focal length will be

PhysicsRay OpticsNEET
Options:
  • A 12 cm
  • B 60 cm
  • C 20 cm
  • D 30 cm
Solution:
1123 Upvotes Verified Answer
The correct answer is: 12 cm
Equivalent focal length

1F=1f1+1f2

 =120+130

∴F=20×3020+30

=60050=12 cm

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