In the figure the intensity of waves arriving at D from two coherent sources s1 and s2 is I0. The wavelength of the wave is λ=4m. Resultant intensity at D will be
2I0
Path difference
Δx=s2D−s1D=5−4=1 m
∴ The corresponding phase difference will be
Φ=2πλ.Δx=(2π4)(1)=π2
Using I=I1+I2+2√I1I2 cosφ
I=I0+I0+2√I0I0 cosπ2=2I0