Types of Waves
Waves can occur whenever a system is disturbed from equilibrium and when the disturbance can travel or propagate from one region of the system to another. Waves can be classified in a number of ways based on the following characteristics
1) On the basis necessity of medium:
i) Mechanical waves: Require medium for their propagation e.g. Waves on string and spring, waves on water surface, sound waves, seismic waves.
ii) Non-mechanical waves: Do not require medium for their propagation are called e.g., light, heat, radio waves, \(\gamma \) – rays, X-rays etc.
2) On the basis of vibration of particle:
On the basis of vibration of particle of medium waves can be classified as transverse waves and longitudinal waves.
3) On the basis of energy propagation:
i) Progressive wave: These waves advance in a medium with definite velocity. These waves propagate energy in the medium e.g. Sound wave and light waves.
ii) Stationary wave: These waves remain stationary between two boundaries in medium. Energy is not propagated by these waves but it is confined in segments e.g. Wave in a string, waves in organ pipes.
4) On the basis of dimension:
i) One dimensional wave: Energy is transferred in a single direction only e.g. Wave propagating in a stretched string.
ii) Two dimensional wave: Energy is transferred in a plane in two mutually perpendicular directions e.g. Wave propagating on the surface of water.
iii) Three dimensional wave : Energy in transferred in space in all direction e.g. Light and sound waves propagating in space.
5) Some other waves:
i) Matter waves : The waves associated with the moving particles are called matter waves.
ii) Audible or sound waves : Range 20 Hz to 20 KHz. These are generated by vibrating bodies such as vocal cords, stretched strings or membrane.
iii) Infrasonic waves : Frequency lie below 20 Hz and wavelengths are greater than 16.6 cm. Example : waves produced during earth quake, ocean waves etc.
iv) Ultrasonic waves: Frequency greater than 20 KHz. Human ear cannot detect these waves, certain creatures such as mosquito, dog and bat show response to these. As velocity of sound in air is 332 m/sec so the wavelength \( \lambda \) < 1.66 cm
v) Shock waves: When an object moves with a velocity greater than that of sound, it is termed as Supersonic. When such a supersonic body or plane travels in air, it produces energetic disturbance which moves in backward direction and diverges in the form of a cone. Such disturbances are called the shock waves.
The speed of supersonic is measured in Mach number. One Mach number is the speed of sound.