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MHT CET202313 May 2023Evening ShiftPhysicsRay OpticsActual

The radii of curvature of both the surfaces of a convex lens of focal length ' f ' and focal power ' P ' are equal. One of the surfaces is made plane by grinding. The new focal length and focal power of the lens is

Options

  1. A2 3 f , 2 3 P
  2. B2 f , P 2
  3. Cf 2 , 2 P
  4. D2 f , P 2

Correct answer

D. 2 f , P 2

Step-by-step solution

From Lens maker's formula, 1 f =( -1) ( 1 R ₁ - 1 R ₂ ) As the radius of both the surfaces is the same, 1 f =( -1) ( 1 R + 1 R ) 1 f = 2 R ( -1) When one surface is plane, R₁=R, R₂= 1 f ^ =( -1) ( 1 R - 1 ) 1 f ^ = 1 R ( -1) f ^ f =2 f ^ =2 f P= 1 f and P^ = 1 f^ P ^ P = f f ^ = 1 2 P ^ = P 2

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