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JEE Advanced2014PhysicsRay OpticsActual

A transparent thin film of uniform thickness and refractive index n 1 = 1.4 is coated on the convex spherical surface of radius R at one end of a long solid glass cylinder of refractive index n 2 = 1.5 , as shown in the figure. Rays of light parallel to the axis of the cylinder traversing through the film from air to glass get focused at distance f 1 from the film, while rays of light traversing from glass to air get

Options

  1. Af 1 = 3 R
  2. Bf 1 = 2.8 R
  3. Cf 2 = 2 R
  4. Df 2 = 1.4 R

Correct answer

A. f 1 = 3 R

Step-by-step solution

For air to glass 1.5 f 1 = 1.4 - 1 R + 1.5 - 1.4 R ∴ f 1 = 3 R For glass to air. 1 f 2 = 1.4 - 1.5 - R + 1 - 1.4 - R ∴ f 2 = 2 R

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