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Manipal MET2013PhysicsRay Optics

The plano-convex lens of focal length 20 cm and 30 cm are placed together to form a double convex lens, the final focal length will be

Options

  1. A12 cm
  2. B60 cm
  3. C20 cm
  4. D30 cm

Correct answer

A. 12 cm

Step-by-step solution

Equivalent focal length aligned & 1 F = 1 t₁ + 1 f₂ &= 1 20 + 1 30 & F= 20 30 20+30 = 600 50 =12 ~cm & F=12 ~cm aligned

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