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AP EAMCET202418 May 2024Morning ShiftPhysicsRay OpticsActual

The focal length of a thin converging lens in air is 20 cm . When the lens is immersed in a liquid, it behaves like a concave lens of power 1 D . If the refractive index of the material of the lens is 1.5 , the refractive index of the liquid is

Options

  1. A5 3
  2. B4 3
  3. C5 4
  4. D7 4

Correct answer

A. 5 3

Step-by-step solution

In air, 1 f ₁ = ( ₂-1 ) ( 1 R ₁ - 1 R ₂ ) (i) In medium, P₂=-1 D f₂= 100 P₂ ~cm =-100 ~cm 1 f ₂ = ( ₂ ₁ -1 ) ( 1 R ₁ - 1 R ₂ ) (ii) From eqns (i) and (ii), we get f₂ f₁ = ( ₂-1 ) ( ₂ ₁ -1 ) aligned & -100 20 = (1.5-1) ( 1.5 ₁ -1 ) = 0.5 ( 1.5 ₁ -1 ) & ₁= 5 3 aligned

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