Velocity of sound waves in air is $330\; m/sec$. For a particular sound in air, a path difference of $40 \;cm$ is equivalent to a phase difference of $1.6 \pi$. The frequency of this wave is... $Hz$
AIPMT 1990, Medium
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(c) Phase difference $=\frac{{2\pi }}{\lambda } \times $ path difference
==>$1.6\pi = \frac{{2\pi }}{\lambda } \times 40$
$ \Rightarrow \lambda = 50 \,cm= 0.5\,m$
==> $v = n\lambda $
==> $330 = 0.5 \times n \Rightarrow n = 660\,Hz$
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