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BITSAT2014PhysicsRay OpticsActual

The magnifying power of a telescope is 9 . When it is adjusted for parallel rays, the distance between the objective and the eye piece is found to be 20 ~cm . The focal length of lenses are

Options

  1. A18 ~cm , 2 ~cm
  2. B11 ~cm , 9 ~cm
  3. C10 ~cm , 10 ~cm
  4. D15 ~cm , 5 ~cm

Correct answer

A. 18 ~cm , 2 ~cm

Step-by-step solution

f ₀ f _ e =9, f ₀=9 f _ e Also f ₀+ f _ e =20( final image is at infinity )9 f _ e + f _ e =20, f _ e =2 ~cm , f ₀=18 ~cm

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