0.5 Longitudinal waves  (Page 2/3)

Wavelength and amplitude

Wavelength

The wavelength in a longitudinal wave is the distance between two consecutive points that are in phase.

The wavelength in a longitudinal wave refers to the distance between two consecutive compressions or between two consecutive rarefactions.

Amplitude

The amplitude is the maximum displacement from equilibrium. For a longitudinal wave which is a pressure wave this would be the maximum increase (or decrease) in pressure from the equilibrium pressure that is cause when a peak (or trough) passes a point.

The amplitude is the distance from the equilibrium position of the medium to a compression or a rarefaction.

Period and frequency

Period

The period of a wave is the time taken by the wave to move one wavelength.

Frequency

The frequency of a wave is the number of wavelengths per second.

The period of a longitudinal wave is the time taken by the wave to move one wavelength. As for transverse waves, the symbol $T$ is used to represent period and period is measured in seconds (s).

The frequency $f$ of a wave is the number of wavelengths per second. Using this definition and the fact that the period is the time taken for 1 wavelength, we can define:

or alternately,

Speed of a longitudinal wave

The speed of a longitudinal wave is defined as:

where

• $v=\mathrm{speed\; in\; m}·\mathrm{s}{}^{-1}$
• $f=\mathrm{frequency\; in\; Hz}$
• $\lambda =\mathrm{wavelength\; in\; m}$

Sound waves

Sound waves coming from a tuning fork are caused by the vibrations of the tuning fork which push against the air particles in front of it. As the air particles are pushed together a compression is formed. The particles behind the compression move further apart causing a rarefaction. As the particles continue to push against each other, the sound wave travels through the air. Due to this motion of the particles, there is a constant variation in the pressure in the air. Sound waves are therefore pressure waves. This means that in media where the particles are closer together, sound waves will travel quicker.