Question

The frequency of sound waves can be expressed in:
A. Hz
B. cycles/second
C. \[{{s}^{-1}}\]
D. All of these

Answer 1

Hint: Frequency is simply the reciprocal of time. And we all know the unit of time is second (s). Thus, by using the mathematical expression of frequency we can find its unit.

Complete step by step answer:
To know the frequency of sound waves, first we know what actually sound waves are.

Sound Waves: Sound waves are the disturbance produced by the vibrating source that travels through the medium. When the particle of the medium sets neighbouring particles into motion, they in turn produce similar motion in others.
The particles of medium do not move forward themselves, but the disturbance that is carried forward. This is what happens in propagation of sound, hence sound can be visualised as a wave.

For example,
If we vibrate a bell the bell first moves forward makes the vibration push the air near to it makes the density of particles higher or makes the pressure high, this region of high pressure known as Compression (C).
When the bell moves backward it creates a region of low pressure or low density known as Rarefaction (R).
This makes the sound wave, which travels through the medium.

Distance between two consecutive compressions (C) and Rarefaction (R) is called wavelength; represented by \[\lambda \].

Time between two consecutive Compression (C) and Rarefaction (R) is called Time Period; represented by T.

In sound waves, when density of medium becomes maximum and after a time it becomes minimum, then again becomes maximum; this makes one complete oscillation.
The number of oscillations per unit time is called frequency of sound wave.
Thus, now you can say, the unit of frequency is cycles per second or per second.
In honour of Physicist Heinrich Rudolph Hertz who worked on electromagnetic theory and sound waves, the SI unit of frequency is termed as Hertz (Hz).

Frequency is represented by \[v\] (pronounced as nu); \[v=\dfrac{1}{T}\].

Answer is option (D). All of these

Note: If there are such types of questions which confuse you to know which one is the right answer, just go through the basic concepts and formula, it will give you the right unit. And always remember the SI unit especially when the SI unit is given in the name of a great scientist or physicist.