If the path difference between two interfering waves at a point is an odd multiple of half the wavelength, what type of interference occurs at that point?

Solution

1. Constructive interference occurs when the path difference is an integer multiple of $\lambda$.
2. Destructive interference occurs when the path difference is $(2n+1)\lambda /2$.
3. This condition corresponds to an odd multiple of half the wavelength.
4. Hence the answer is (B).