LONGITUDINAL WAVES

1. Characteristics of longitudinal waves

Longitudinal waves are mechanical waves where the disturbance is transmitted in a direction PARALLEL to the direction of travel of the waves. Both transverse waves and longitudinal waves may be demonstrated using a long flexible spring.

Sound waves and the so-called P-waves produced by earthquakes are examples of longitudinal waves. They require a medium in which to propagate.

Longitudinal waves travel through a fluid by creating regions of COMPRESSION and RAREFACTION of the fluid, which travel in the direction of the wave. The WAVELENGTH, λ, is the distance between the centers of two consecutive zones of compression or rarefaction, as shown in the above diagram. A particle, P, of the fluid will oscillate in a range 2A, where A is the amplitude of the wave.

The velocity, v, of the wave is the velocity at which the zones of compression and rarefaction travel in the direction of the wave (). As in the case of transverse waves discussed in Grade 10, the FREQUENCY of the wave is given by

The unit of frequency is the HERTZ, Hz where 1 Hz = 1 s-1. The PERIOD, T, of the wave is the time taken for the center of a zone to move one wavelength in the direction of travel. It is the reciprocal of the frequency: T = 1/f.

2. Additional questions