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KCET2008PhysicsRay Optics

A convex and a concave lens separated by distance are then put in contact. The focal length of the combination

Options

  1. Adecreases
  2. Bincreases
  3. Cbecomes 0
  4. Dremains the same

Correct answer

A. decreases

Step-by-step solution

When two lenses are placed coaxially at a distance from each other, then equivalent focal length ( ) is given by 1 F = 1 f₁ + 1 f₂ - d f₁ f₂ When the lenses are put together. d =0 Hence, the focal length of the combination will decrease.

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