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JEE Main20203 Sep 2020Evening ShiftPhysicsRay OpticsActual

Two light waves having the same wavelength λ in vacuum are in phase initially. Then the first wave travels a path L 1 through a medium of refractive index n 1 while the second wave travels a path of length L 2 through a medium of refractive index n 2 . After this the phase difference between the two waves is:

Options

  1. A2 π λ L 2 n 1 - L 1 n 2
  2. B2 π λ L 1 n 1 - L 2 n 2
  3. C2 π λ n 1 L 1 - n 2 L 2
  4. D2 π λ n 2 L 1 - n 1 L 2

Correct answer

C. 2 π λ n 1 L 1 - n 2 L 2

Step-by-step solution

The optical path between any two points is proportional to the time of travel. The distance traversed by light in a medium of refractive index μ in time t is given by d = vt .......(i) Where v is velocity of light in the medium. The distance traversed by light in a vacuum in this time, s = c t = c × d v [from equation (i)] = d c v = μd .....(ii) (Since μ = c v ) This distance is the equivalent distance in vacuum and is called optical path. Here, optical path for first ray = n 1 L 1 Optical path

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