Types of Waves
Category : JEE Main & Advanced
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 (Infrared), 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. Transverse and longitudinal waves
| Transverse waves | Longitudinal waves |
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Particles of the medium vibrates in a direction perpendicular to the direction of propagation of wave.
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Particles of a medium vibrate in the direction of wave motion.
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It travels in the form of crests (C) and troughs (T).
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It travels in the form of compression (C) and rarefaction (R).
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Transverse waves can be transmitted through solids, they can be setup on the surface of liquids. But they can not be transmitted into liquids and gases.
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These waves can be transmitted through solids, liquids and gases because for these waves propagation, volume elasticity is necessary.
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| Medium should posses the property of rigidity | Medium should posses the property of elasticity |
| Transverse waves can be polarised. | Longitudinal waves can not be polarised. |
| Movement of string of a sitar or violin, movement of the membrane of a Tabla or Dholak, movement of kink on a rope, waves set-up on the surface of water. | Sound waves travel through air, Vibration of air column in organ pipes Vibration of air column above the surface of water in the tube of resonance apparatus |
(3) On the basis of energy propagation
(i) Progressive wave : These waves advances 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 remains stationary between two boundaries in medium. Energy is not propagated by these waves but it is confined in segments (or loops) 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. These waves are used for navigation under water (SONAR). They are used in ultrasonography (in photography or scanning soft tissue of body). Their used to repel mosquitoes or attract fishes
(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 disturbance are called the shock waves.
The speed of supersonic is measured in Mach number. One mach number is the speed of sound.
Mach Number = \[\frac{\text{Velocity}\,\text{of}\,\text{source}}{\text{Velocity}\,\text{of}\,\text{sound}}\].
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