# Waves

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THE NATURE OF WAVES

We use waves to transfer energy and information.  The direction of travel of the wave is the direction in which the wave transfers energy.  There are different types of wave:

• A transverse wave is where the oscillation of the particles is perpendicular to the direction in which the wave travels
• A longitudinal wave is where the oscillation of the particles is parallel to the direction of travel of the wave.  A longitudinal wave has rarefactions and compressions

Electromagnetic waves can travel through a vacuum.  There are no particles in an electromagnetic wave, as these waves are oscillations in electric and magnetic fields. The oscillations are perpendicular to the direction of travel, so electromagnetic waves are all transverse.  Mechanical waves such as waves on springs may be transverse or longitudinal.  Sound waves are longitudinal waves.

MEASURING WAVES

The amplitude of a wave is the height of the wave crest or the depth of the wave trough from the position at rest.  The greater the amplitude of a wave, the more energy it carries.  The wavelength of a wave is the distance from one crest to the next crest or from one trough to the next trough.  The frequency of a wave is the number of wave crests passing a point in one second.  The unit of frequency is the hertz, Hz.  The speed of a wave is given by the equation:

v = f x lambda, where v = wave speed in m/s, f = frequency in Hx and lambda is the wavelength in metres.

The wavelength of a longitudinal wave is the distance from the middle of compression to the middle of the next compression, or the middle of one rarefaction to the middle of the next rarefaction.  The frequency of a longitudinal wave is the number of compressions passing a point every second.

WAVE PROPERTIES: REFLECTION

The image seen in a mirror is due to the reflection of light.  The incident ray is the ray that goes towards the mirror.  The reflected ray is the one coming away from the mirror.  The normal is a line perpendicular to the mirror at the point where the incident ray hits