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# Terminologies in Progressive Wave Motion

• Amplitude
• Period
• Wavelength
• Frequency
• Wave velocity
• Phase or phase angle (O)
• Phase difference
• Path difference
• Time difference

### Explanation:

Amplitude (A): The amplitude of a wave is the maximum displacement of any particle of the medium from its equilibrium position.

Period (T): Period (T) of a wave is the time taken by any particle of the medium to complete one vibration during a period (T).

Wavelength (λ): Wavelength (λ) is equal to the distance between two consecutive particles of the medium which are in the same state of vibration. It is equal to the distance travelled by the wave by its time period (T).

Frequency (f): It is the number of vibrations made per second by any particles of the medium (f = 1/T). Since the frequency of a wave is a characteristic property of the source which is producing the wave motion, hence, the frequency of a wave does not change when a wave travels from one medium to another medium.

Phase or Phase Angle (Φ): It represents the state of vibration of the particle of a medium with respect to its mean position.

Phase Difference Δ(Φ): It represents the different state of vibration of a particle at two different instants (or) any pair of particles at the same instant. ΔΦ = Φ2 – Φ1.

Wave Velocity (v): It is the distance travelled by the wave in one second (v = λ/T). It is determined by the mechanical properties of the medium through which the wave propagates. The velocity of wave motion is measured with respect to the medium, the wave velocity changes when the medium is in motion i.e. speed of sound through air changes when the wind is blowing.

There are two velocities associated with a wave. One is the wave velocity and the other one is particle velocity (which is the speed with which the particle of the medium vibrate when the wave passes through the medium).

Path Difference (Δx) or (x): It indicates the distance between two points measured along the direction of propagation of the wave through the medium.

Time Difference (ΔT): It indicates the time taken by the wave to travel from one point to another through the medium.