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A convex lens made of glass (refractive index =1.5 ) has focal length 24 cm in air. When it is totally immersed in water (refractive index =1.33 ), its focal length changes to

Options

  1. A24 cm
  2. B96 cm
  3. C48 cm
  4. D72 cm

Correct answer

B. 96 cm

Step-by-step solution

aligned & 1 8 = ( _ _ s -1 ) [ 1 R ₁ - 1 R ₂ ] & 1 24 =(1.5-1) [ 2 R ] ...(i) & 1 f ^ = ( 1.5 1.33 -1 ) ( 2 R ) & 1 f ^ = ( 1.5 3 4 -1 ) 2 R ...(ii) aligned (i) divided by (ii) aligned & f ^ 24 =4 & f ^ =96 ~cm aligned

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