Properties of Mechanical waves and Electromagnetic waves

From Online Sciences - October 6, 2017

There are two types of motion , which are Translational motion and Periodic motion ,Translational motion is the motion that has starting point and end point ,Periodic motion is the motion that repeats itself regularly in equal intervals of time ,Periodic motion can be classified into wave motion and oscillatory motion .

Wave motion

When we throw a stone in water , The collision of the stone with water is a source of disturbance , This disturbance propagates on the surface of water in the form of uniform concentric circles , whose center is the position at which the stone falls .

These circles transfer the energy in the same direction of their propagation , These circles are called water waves and its propagation represents the wave motion , Wave is the disturbance that propagates and transfers the energy in the direction of its propagation .

Types of waves

There are many types of waves around us , some waves can be seen such as the water waves , other waves can not be seen but we can detect them such as radio and TV waves , Waves can be classified into Mechanical waves and Electromagnetic waves .

Types of mechanical waves are transverse waves ( such as water waves ) and longitudinal waves ( such as sound waves ) , Types of Electromagnetic waves aretransverse waves only ( such as radio waves ) .

Mechanical waves

Sources : Mechanical waves are produced from vibrating source that transmits the disturbance through the medium , Propagation medium : They propagate through materialistic media only .

Mechanical wave is a disturbance that propagate in materialistic media , such as water waves , sound waves , waves that propagate in strings during its vibration .

Conditions of mechanical waves

Oscillatory motion

It is the objects motion at the two sides of its original position ( rest position ) and repeated in equal intervals of time , There are some concepts related to oscillatory motion such as Complete oscillation , Amplitude , Frequency and Periodic time .

Complete oscillation

When the pendulum moves from A to B then to C and returns back to A ( A B C A ) , It has passed by A two successive times in the same direction ( in the same phase ) , So , it makes a complete oscillation .

Phase is the position and the direction of the medium particles at a certain instant , Complete oscillation is the motion of the oscillating body when it passes one point along the path of its motion twice successively in the same direction .


When the pendulum moves away from its rest position , it makes a displacement , where this displacement ( d ) is a vector quantity and measured in meter ( m ) , Displacement ( d ) is the distance of the vibrating body at any instant from its rest position or its equilibrium origin .

The maximum displacement made by the pendulum ( the distance AB or AC ) is called amplitude , The amplitude represents quarter of a complete oscillation , The measurement unit of amplitude is meter ( m ) .

Amplitude is the maximum displacement of the vibrating body away from its original position or it is the distance between two points along the path of the vibrating object , where the velocity at one point is maximum and zero at the other .

When the amplitude of a vibrating body = 20 cm , this means that the maximum displacement of the vibrating body away from its original position = 20 cm .


When the pendulum makes a number of oscillation in a certain time , the number of oscillations which it makes in one second is called frequency , the frequency ( ) can be determined from the relation :

Frequency= n ( Number of oscillations ) / t ( Time )

The measurement unit of frequency is Hertz ( Hz ) which is equivalent to oscillation/sec or cycle/sec or second1 , Frequency () is the number of complete oscillations made by a vibrating body in one second .

When the frequency of a tuning fork = 50 Hz , this means that the fork makes 50 complete oscillations ( vibrations ) in one second .

Periodic time

The time taken by the pendulum to pass by the same point two successive times in one direction ( to make a complete oscillation ) is called the periodic time , the periodic time ( T ) can be determined from the relation :

T = t ( time in seconds ) / n ( Number of complete oscillations )

T = 4 Time of amplitude

Periodic time ( T ) is the time taken by a vibrating body to make one complete oscillation or it is the time taken by the vibrating body to pass by the same point along the path of its motion two successive times in the same direction .

The measurement unit of periodic time is second ( s ) , When the periodic time of a vibrating body = 2 s , this means that the vibrating body takes 2 s to make one complete oscillation .

= 1 / T

Frequency = Reciprocal of the periodic time , So , the frequency is inversely proportional to the periodic time .

Types of mechanical waves

Transverse waves

= X ( Total distance ) / n ( Number of waves )
= n ( number of waves ) / t ( Time )

Longitudinal waves

Electromagnetic waves

1 1 = 2 2
1 / 2 =2 / 1
1 / 2 = V1 / V2


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