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JEE Main202131 Aug 2021Morning ShiftPhysicsRay OpticsActual

An object is placed at the focus of concave lens having focal length f . What is the magnification and distance of the image from the optical centre of the lens?

Options

  1. A1 4 , f 4
  2. B1 2 , f 2
  3. CVery high, ∞
  4. D1 , ∞

Correct answer

B. 1 2 , f 2

Step-by-step solution

1   F = 1 v - 1 u Put u = - f and F = - f 1 - f = 1 v - 1 - f ;    - 1 f = 1 f - 1 v ; - 2 f = 1 v ⇒ v = - f 2 Magnification = v / u = - f 2 ( - f ) = 1 2

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