Geometrical OpticsHard

Question

A parallel monochromatic beam of light is incident normally on a narrow slits. A diffraction pattern is formed on a screen placed perpendicular to the directionof the incident beam. At the first minimum of the diffraction pattern, the phase difference between the rays coming the two edges of the slits is

Options

A.zero
B.π / 2
C.π
D.2π

Solution

         
At first minima, b sin θ = λ
or    b θ = λ   or  
          or            .......(i)
Now, at P (first minima) path difference between the rays reaching from two edges (A and B) will be
      ᐃx =       (Compare with ᐃx = in YDSE)
or ᐃx = λ           [From Eq. (i)]
Corresponding phase difference (φ) will be
    

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