Q.

In Young's double slit experiment, light from two identical sources are superimposing on a screen. The path difference between the two lights reaching at a point on the screen is 7λ/4. The ratio of intensity of fringe at this point with respect to the maximum intensity of the fringe is                    [2024]

1 14  
2 13  
3 34  
4 12  

Ans.

(4)           

                   Path difference,Δx=7λ4

                   Phase difference,ϕ=2πλΔx=2πλ×7λ4=7π2

                   Intensity,I=Imaxcos2(ϕ2)

                   IImax=cos2(ϕ2)=cos2(7π2×2)=cos2(7π4)

                   =cos2(2π-π4)=cos2π4=12