Question

Sound waves of frequency 600 Hz fall normally on perfectly reflecting wall. The distance from the wall at which the air particles have the maximum amplitude of vibration is
(speed of sound in air = 330 m/s)

• A. 13.75 cm
• B. 40.25 cm
• C. 70.5 cm
• D. 60.75 cm

Answer 1

Answer: (A)

13.75 cm

Stationary waves will be formed due to the interference of incident and the reflected sound waves. At the reflecting surface, displacement node will be formed.

Let the wavelength of the original wave be $\lambda .$

Given: $v=330m/s\nu =600Hz$

$v=\nu \lambda$ gives $330=600\times \lambda$

$⟹\lambda =0.55m$

As the distance between the point of maximum amplitude (displacement antinode) and the reflecting surface (displacement node) $d=\frac{\lambda }{4}$

$⟹d=\frac{0.55}{4}=0.1375m=13.75cm$