Question

Two coherent sources produce a dark fringe when the path difference between the interfering waves is

Answer 1

Dark fringe

1. Dark fringes are produced when there is destructive interference.
2. Destructive interference can be produced if the resultant amplitude or the intensity is zero.
3. In destructive interference the waves are generally out of phase.
4. The path difference, in this case, must be half an integral number of wavelengths.

Hence, to produce a dark fringe, the path difference must be$\frac{n}{2}$, where $n$ is an integer, that refers to the number of wavelengths.