Question

769Hz longitudinal wave in air has a speed of 344m/s. How much time is required for the phase to change by 90 degrees at a given point in space?

• A. 0.325 ms
• B. 3.25 ms
• C. 32.5 ms
• D. 325 ms

Answer 1

The correct option is A 0.325 ms

Given that,

The frequency of wave is $\nu =769Hz$.

The speed of wave is $v=344m{s}^{-1}$.

We know, the frequency of a wave is the number of oscillations per

unit time. The period (T) of a wave is the time that it takes for one complete oscillation, i.e., to change its phase through ${360}^{\circ }$.

Hence,

$T=\frac{1}{\nu }$

$T=\frac{1}{769}$

$T=0.0013s$

$T=1.3ms$

Here, the phase change is 90 degrees at a given point in space.

$\frac{90}{360}=\frac{1}{4}$

Hence, the time period required to complete one fourth oscillation is

$T=\frac{1.3}{4}=0.325ms$