What is the condition for constructive interference in terms of path difference $\Delta x$ for light waves of wavelength $\lambda$?

Solution

1. Constructive interference occurs when two waves overlap in phase, resulting in a maximum amplitude.
2. This condition is met when the path difference $\Delta x$ between the two waves is an integer multiple of the wavelength $\lambda$.
3. The mathematical expression for this condition is $\Delta x=n\lambda$, where $n$ is an integer ($n=0,1,2,\dots$).
4. Hence the answer is (A).