Classification Of Wave Motion

Classification Of Wave Motion

On the Bases of Necessity of Medium Required

MECHANICAL WAVES
The wave which propagates only in a material medium are called elastic or mechanical waves.
Example: Sound waves, Water waves (ripples), Waves on stretched strings, Earthquake waves and the Shock waves produced by a supersonic aircraft are mechanical (or elastic) waves.

ELECTROMAGNETIC WAVES
Wave which do not require any material medium for their propagation are called electromagnetic waves.
Example: Light waves, Radio waves, Television waves, and X-rays are electromagnetic waves. Thus, Light waves, Radio and Television waves, and X-rays can also travel through vaccum.

Difference between mechanical waves & electromagnetic waves

Mechanical wavesElectromagnetic waves
1.Mechanical waves need a material medium for their propagation. These waves cannot travel through vacuum.Electromagnetic waves do not need any material medium for their propagation. These waves can travel through vacuum.
2.Speed of mechanical waves are low and depends upon the source and the medium through  which they travel.(EMW) a electromagnetic waves travel with the speed of light (3 × 108 m/s) in vaccum. The speed of an electromagnetic wave in any material medium is less than that in vaccum.
3.Mechanical waves are due to the vibrations of the particles of the medium.(EMW) a electromagnetic  waves are not due to vibration of medium particles
4.Mechanical waves may be longitudinal or transverse waves.Electromagnetic are transverse waves.
5.Example: Sound waves, water waves, string waves are mechanical waves.Examples: Light waves, radio and TV waves, and X-rays are electromagneti


TRANSVERSE WAVES 
On the Basis of mode of Vibration of the Particle

A wave in which the particles of the medium oscillate about their mean position in a direction perpendicular to the direction of propagation of the wave is called a transverse wave.
Transverse waves can travel through solids and over the surface of liquids, but not through gases.

Examples: Following are the examples of transverse waves

  1. The water waves (ripples) produced on the surface of water is transverse waves. In water waves, the molecules of water move up and down from their mean positions.
  2. A pulse on a slinky when it is given a jerk is a transverse wave.
  3. All electromagnetic waves, e.g., light waves, radio waves etc., are transverse waves.
  4. The waves produced in a stretched string when plucked are transverse waves. When a string of sitar (a musical instrument) or guitar is plucked, transverse waves are produced in the string.

Graphical Representation:
Displacement-distance-graph-for-a-transverse-waves
(a) Crest: The highest point on the hump in a transverse wave is called a crest. Thus, the point of maximum positive displacement on a transverse wave is called a crest.
(b) Trough: The lowest point on the depression in a transverse wave is called a trough. Thus, the point of maximum negative displacement on a transverse wave is called a trough.

LONGITUDINAL WAVES
A wave in which the particle of the medium oscillate (vibrate) to and fro about their mean position in the direction of propagation of the wave is called a longitudinal wave.
Longitudinal waves can be produced in any medium, viz., in solids, liquids and in gases.
Example:
(i) Sound waves are longitudinal waves.
(ii) The waves produced in a spring (slinky) by compressing a small portion of it and releasing are longitudinal waves.

Graphical Representation:
Displacement-distance-graph-for-a-transverse-waves-1
(a) Compression: The part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is called a compression.
(b) Rarefaction: The part of a longitudinal wave in which the density of the particles of the medium is lesser than the normal density is called a rarefaction.

What is the difference between longitudinal and transverse waves?

 LongitudinalTransverse waves
1In a longitudinal wave the particles of the medium oscillate along the direction of propagation of the wave.In a transverse wave, the particles of the medium oscillate in a direction perpendicular to the direction of propagation of the wave
2Longitudinal waves can propagate through solids, liquids, as well as gases.Transverse waves can propagate through solids, and over the surface of liquids, but not through gases.
3Longitudinal waves consist of compression and rarefactions.Transverse waves consist of crests and troughs.

Transverse Waves and Longitudinal Waves Experiment

Aim: To study transverse waves and longitudinal waves using a slinky spring.
Material: Ribbon
Apparatus: Slinky spring
Method:

Classification Of Wave Motion 1

    1. A slinky spring is placed on the floor. One end of it is tied to the leg of a table.
    2. A short length of ribbon is tied to any part of the spring between the two ends.
    3. A set of transverse waves is produced by vibrating the spring at right angles with it as shown in Figure The movement of the ribbon is observed.
      Classification Of Wave Motion 2
    4. A set of longitudinal waves is produced by vibrating the spring in a to-and-fro direction as shown in Figure The movement of the ribbon is observed.
      Classification Of Wave Motion 3

Observations:

  1. In step 3, the ribbon is displaced in an up-and-down motion which is perpendicular with the direction of the propagation of the waves.
  2. In step 4, the ribbon is displaced in a to-and-fro motion which is parallel with the direction of the propagation of the waves.

Discussion:

  1. The ribbon tied to the slinky spring represents the particles of the medium of the waves.
  2. Step 3 shows that any point on the spring is displaced in an up-and-down motion which is perpendicular with the direction of the propagation of the waves.
  3. Step 4 shows that any point on the spring is displaced in a to-and-fro motion which is parallel with the direction of the propagation of the waves.

Conclusions:

  1. For transverse waves, the particles of the medium move in a direction perpendicular to the direction of the propagation of the waves.
  2. For longitudinal waves, the particles of the medium move in a direction parallel to the direction of the propagation of the waves.