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KCET2012PhysicsRay Optics

A point source of light is kept below the surface of water (n_ w =4 / 3 ) at a depth of 7 ~m . The radius of the circular bright patch of light noticed on the surface of water is

Options

  1. A7 ~m
  2. B3 7 ~m
  3. C3 ~m
  4. D7 3 ~m

Correct answer

C. 3 ~m

Step-by-step solution

When the ray of light is incident from water-air interface at critical angle ( _ c ) , the refracted ray becomes parallel to the interface. Hence, the radius of the circular bright patch of light noticed on the surface of water is given by aligned R &= h _ c &= 7 _ c _ c = 7 1 / 1- 1 ² = 7 ²-1 =3 ~m aligned

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