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AP EAMCET2011PhysicsRay Optics

The focal length of a lens of dispersive power 0.45 which should be placed in contact with a convex lens of focal length 84 ~cm and dispersive power 0.21 to make the achromatic combination from the two lenses, in cm is

Options

  1. A45
  2. B90
  3. C180
  4. D-180

Correct answer

D. -180

Step-by-step solution

Here, ₁=0.45 ₂=0.21 and f₂=84 ~cm As the lens are kept is contact it is achromatic condition. aligned ₁ ₂ & =- f₁ f₂ 0.45 0.21 & =- f₁ 84 f₁=- 45 84 21 & =-180 ~cm aligned

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