Important terms, Meanings, Definitions of Waves (Physics)

Some terms related to Transverse Waves:

Transverse Wave : It is that type of wave motion in which  the particles of the medium vibrate about their mean position in a direction at right angles to the direction of propagation (motion) of the wave.
                       

Crest : A portion in the medium at the maximum distance above the mean position is called a crest.

Trough : A portion in the medium at the maximum distance below the mean position is called a trough.

Wavelength (λ) :  The distance between two nearest crests or troughs is called wavelength. It is denoted by λ , and pronounce as "lambda".

Wave Velocity(v) : The velocity with which wave motion travels (propagates) through medium is called wave velocity. It is denoted by v.

Amplitude (a) : Height of crest and depth of Trough from the mean position is called Amplitude . It is the maximum displacement of particle above the mean position. It is denoted by a.

Frequency (n) : The number of vibrations or disturbances produced in one second (unit time) is called frequency. It is denoted by n.

Relation between Frequency, Wavelength and Wave Velocity.

                                           v = nλ   i.e.,

                        Wave Velocity = Frequency  X  Wavelength

Some terms related to Longitudinal Waves:

Longitudinal Wave : It is that type of wave motion in which the particles of the medium vibrate back and forth about their mean positions parallel to the direction of propagation (motion) of the wave.

Compression or Condensation :  In a longitudinal wave, the region in which the distance between the particles of the medium is less than their normal distances is called a compression.

or

A compression indicates temporary reduction in volume and consequently an increase in density.

Rarefaction : In a longitudinal wave, the region in which the distance between the particles of the medium is more than their normal distances is called rarefaction.
                 In this region, the particles of the medium move in the backward directions as shown in fig below:

                                  

The density of the medium around such particles is less than their normal density. 

Wavelength (λ) : In longitudinal wave, it is defined as the distance between two successive compressions or rarefactions.

Wave Velocity (v) : The velocity with which a longitudinal wave travel (propagates) through a medium is called wave velocity.

or

The distance travelled by the wave(transverse or longitudinal) per unit time is called wave velocity. It is denoted by v.

Amplitude (a) : It is the maximum displacement of each particle from its undisturbed position . It is the measure of extent of region or space of compression or of rarefaction.

Frequency (n) : It is the number of waves competed by a longitudinal wave or disturbance in one second. Its unit is Hertz (Hz).

Displacement (y): Displacement of a vibrating particle at any instant is the distance through which it has travelled from its mean position in the positive direction.

Wavelength (λ): In case of transverse waves, it is the distance between two consecutive troughs or crests. 
In case of longitudinal waves, it is the distance between nearest compressions or two nearest rarefactions.
Its S.I unit is metre, but a smaller unit is Å (Angstrom) is used preferably.

[1  Å  = 10⁻¹⁰ m].

Time Period : The time taken by a vibrating body  to complete one vibration is called time period. It is denoted by T. 

Frequency : The number of vibrations made by a vibrating body in one second is called frequency. It is denoted by n.

or

frequency of wave is the number of waves crossing any point in one second.

Relation Between Time-Period and Frequency:

Let a particle having time period T seconds completes n vibrations in 1 second.

                                 Frequency =  n  vibration/second

Number of vibrations completed in T second = 1

Number of vibrations completed in 1 second =1/T.

Acc. to definition of frequency, no. of vibrations completed in 1 second is called frequency.

hence                              n = 1/T

Unit of frequency is cycles/second or Hertz (Hz).

Relation Between Wave Velocity, Wave length and Frequency:

                                     v = nλ

where v is wave velocity

          λ is wavelength

          n is frequency

from definition,

                       V= Distance travelled / Time taken

                       v = λ/T

                        v = 1/T X λ                [n=1/T]

                        v  = nλ   

Courtesy:R.A.Banwat
Courtesy: tutorvista
Courtesy :everythingscience.co
Courtesy : earthsci.org