The intensity at a point in Young's double slit experiment is given by I=Imaxcos2(2ϕ)
Given I=43Imax
43Imax=Imaxcos2(2ϕ)
cos(2ϕ)=23
2ϕ=6π
ϕ=3π
The phase difference ϕ is related to the path difference Δx by ϕ=λ2πΔx
λ2πΔx=3π
Δx=6λ
Comparing with Δx=xλ, we get x=6
Answer: 6