Question

By the principle of interference, condition for constructive
interference in terms of the path difference?

• A. $n^{-1}\lambda$
• B. $n\lambda$
• C. $n\lambda {}^2$
• D. $n\lambda {}^4$

Answer 1

The correct option is B $n\lambda$

When the crest and trough of one wave meet the crest and trough of other wave, respectively, then we say that constructive interference between the waves takes place.
Condition for constructive interference is that the path difference between the two waves must be an integral multiple of the wavelentgth of wave.
So, path difference $\Delta x=n\lambda$
where $n$ must be an integer.