# Wave, its types and characteristics

Wave motion and wave:

• A wave motion is a kind of disturbance which is transferred from one part of the medium to another part due to repeated periodic motion of particles of the medium about their mean position.
• Wave is the disturbance which travels through the medium with certain definite velocity without any change in its form.

Types of waves:

On the basis of whether a wave needs medium for its propagation or not, there are two kinds of waves:

Electromagnetic waves:

• The wave that doesn’t need medium for its propagation is called electromagnetic wave. Light wave, heat radiation (infrared rays), ϒ-rays, X-rays and microwaves are electromagnetic waves (non-mechanical waves).

Mechanical waves:

• The wave that needs material medium for its propagation is called mechanical wave. Sound waves, waves in stretched strings, waves in organ pipes, water waves, and waves in spring are mechanical waves.
• Mechanical waves transfer energy and momentum through the limited motion of particles with the medium remaining at its own place.
• For the propagation of mechanical wave through a medium, the medium must be elastic; it should have inertia and should have low degree of damping.

On the basis of direction of vibration of particles of a medium, there are two types of waves:

Longitudinal waves:

• The wave in which particles of the medium oscillate in simple harmonic motion about their mean position along the direction of propagation of wave is called longitudinal wave. Sound waves, waves in long coil or spring are longitudinal waves.
• Longitudinal wave results in compressions and rarefactions in the medium.

Transverse waves:

• The wave in which particles of the medium oscillate in simple harmonic motion about their mean position in a direction perpendicular to the direction of propagation of wave is called transverse wave.
• Waves in stretched string, light wave, heat wave are transverse waves.
• Transverse wave results in crests and troughs in a medium.
• Only transverse waves can be polarized, longitudinal waves can’t be. Hence, polarization is a characteristic to decide whether a wave is transverse or longitudinal.

On the basis of transmission of energy, there are two types of waves:

Progressive wave:

• The wave in which the disturbance is continuously transmitted along the direction of propagation of wave and energy is being transferred along with the disturbance from one place to another is called progressive wave.

Stationary wave or standing wave:

• The wave in which the disturbance is transmitted but energy is confined within a certain region is called standing or stationary wave.

Characteristics of wave:

1. Displacement and Amplitude:
• The instantaneous position of any particle of the medium in which the wave is propagating, is called displacement of the particle from its equilibrium position.
• The maximum displacement of the particle from the mean position is called amplitude of the wave.  Amplitude is a vector quantity.
2. Oscillation and Time period:
• A complete wave motion containing one crest and one trough (for transverse wave) and one compression and one rarefaction (for longitudinal wave) is called one oscillation or wave form.
• The time taken to complete one oscillation is called time period and is denoted by T.
3. Frequency:
• The number of oscillations made by vibrating body in one second is called frequency and is denoted by f or n.
• Frequency depends on the source and not on the medium.
• Frequency doesn’t change when wave travels from one medium to another medium.
4. Wavelength:
• The distance in the direction of propagation of wave in which the wave gets repeated itself is called wavelength.
• It is the distance between two consecutive crests or troughs (for transverse waves) and the distance between two consecutive compressions and rarefactions (for longitudinal waves).
• It is denoted by Lambda (λ).
• Wavelength depends on the nature of medium and the source producing wave.
5. Wave velocity:
• The distance travelled by wave in one second is called wave velocity.
• It is denoted by V.

V= fλ   (where, f is the frequency and λ is the wavelength of the wave)

• When wave travels from one medium to another medium, the velocity of the wave changes.

6. Phase:

• The quantity that gives the state of the vibrating particle regarding to its position and direction of motion is called phase.
• It is denoted by Phi (φ).