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AIIMS2008PhysicsRay Optics

Assertion: A double convex lens (( =1.5) ) has focal length (10 ~cm ). When the lens is immersed in water (( =4 / 3) ) its focal length becomes (77 ~cm ). Reason : ( 1 f = _g- _w _w ( 1 R₁ - 1 R₂ ) )

Options

  1. AIf both assertion and reason are true and reason is the correct explanation of assertion
  2. BIf both assertion and reason are true but reason is not the correct explanation of assertion
  3. CIf assertion is true but reason is false
  4. DIf both assertion and reason are false.

Correct answer

A. If both assertion and reason are true and reason is the correct explanation of assertion

Step-by-step solution

aligned & 1 f = ( ^a _g-1 ) [ 1 R₁ - 1 R₂ ] & = ( _g _w -1 ) ( 1 R₁ - 1 R₂ ) & 1 f = ( _g- _w _w ) [ 1 R₁ - 1 R₂ ] & = ( 1.5-1.33 1.33 ) [ 1 20 + 1 20 ] & 1 f = 0.13 2 20 f= 20 0.26 & f=76.92 ~cm . & aligned

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