# Two water waves

The above diagram shows two water waves, at a particular instant, generated by two respective wave sources $$S_1$$ and $$S_2.$$ The two waves have the same phase, amplitude and frequency. Solid lines represent the peaks of the waves, whereas dotted lines represent the bottoms of the waves. Which of P, Q and R is the point where the path difference between the two waves is an odd multiple of a half wave length?

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