Q.

In the Young's double slit experiment using a monochromatic light of wavelength λ, the path difference (in terms of an integer n) corresponding to any point having half the peak intensity is                          [2013]

1 (2n+1)λ2  
2 (2n+1)λ4  
3 (2n+1)λ8  
4 (2n+1)λ16  

Ans.

(2)

Intensity,  I=I0cos2ϕ2  where I0 is the peak intensity.

Here,  I=I02,  ∴ I02=I0cos2ϕ2,  ∴ ϕ=π2(2n+1)

∴  ϕ=π2, 3π2, 5π2, …

And path difference,

Δx=(λ2π)ϕ

∴  Δx=λ4, 3λ4, …, (2n+1)λ4