Wave Motion 5 Question 21
21. A plane progressive wave of frequency $25 Hz$, amplitude $2.5 \times 10^{-5} m$ and initial phase zero propagates along the negative $x$-direction with a velocity of $300 m / s$. At any instant, the phase difference between the oscillations at two points $6 m$ apart along the line of propagation is …… and the corresponding amplitude difference is …… m. (1997, 1M)
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Answer:
Correct Answer: 21. $\pi, zero$
Solution:
- $v=300 m / s, \quad f=25 Hz$
$\therefore$ Wavelength $\lambda=\frac{v}{f}=\frac{300}{25}=12 m$
(a) Phase difference $\Delta \phi=\frac{2 \pi}{\lambda}$ (path difference)
$$ =\frac{2 \pi}{12} \times 6=\pi $$
(b) In plane progressive wave amplitude does not change.
