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MHT CET20228 Aug 2022Morning ShiftPhysicsRay OpticsActual

A convex lens A of focal length 20 ~cm and a concave lens B of focal length 56 ~cm are kept along the same axis with the distance d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then the magnitude of distance d (in cm ) is

Options

  1. A25
  2. B36
  3. C30
  4. D50

Correct answer

B. 36

Step-by-step solution

d=f₁+f₂ By using the formula 1 f₁ + 1 f₂ - d f₁ f₂ = 1 f For the emergent beam to parallel aligned & P=0 or f= & 1 20 ~cm + 1 (-56 ~cm ) - d 20 ~cm (-56 ~cm ) =0 & d=20 ~cm +(-56 ~cm )=-36 ~cm aligned

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