Write down the condition of constructive interference.

(N/A) Constructive interference occurs when two light waves meet in phase,resulting in an increase in amplitude.
For two waves with a path difference $\Delta x$,the condition for constructive interference is that the path difference must be an integral multiple of the wavelength $\lambda$.
Mathematically,this is expressed as: $\Delta x = n\lambda$,where $n = 0, 1, 2, 3, \dots$
Alternatively,in terms of phase difference $\phi$,the condition is $\phi = 2n\pi$,where $n$ is an integer.