• Wave theory is a branch of physics that studies the properties of waves.
  • A wave can be described as a disturbance that travels through a medium from one location to another location.
  • They consists of disturbances which transfer the energy in the direction the wave travels without transferring matter.
  • Crest: A crest is a point on a surface wave where the displacement of the medium is at a maximum.
  • Trough: A trough is the opposite of a crest, so the minimum or lowest point in a cycle.
  • Amplitude: It is the distance from the centre line to the top of a crest or to the bottom of a trough.  
  • Wavelength: The wavelength can be measured as the distance from crest to crest or from trough to trough.
      The waves are classified mainly two types:
  • Mechanical 
  • Electromagnetic 
      - Mechanical Waves:
  • A mechanical wave is a wave acts as disturbance, and therefore travels through a  material medium.
  • While waves can move over long distances, the movement of the medium of transmission the material is limited. 
  • Therefore, oscillating material does not move far from its initial equilibrium position.
  • Mechanical waves are of two types:
     - Longitudinal waves:  
  • These waves occur when the oscillations are parallel to the direction of energy transfer.
  • It is a wave in which particles of the medium move in a direction parallel to the direction that the wave moves.


  • The longitudinal waves travel through a medium in the form of compression and rarefaction. 
  • Compression: It happens when molecules are forced, or pressed, together. 
  • Rarefaction: it occurs when molecules are given extra space and allowed to expand.

     Transverse waves:
  • These waves occur when a disturbance creates oscillations perpendicular at right angles to the direction of energy transfer.
  • It is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves.
  
  • The transverse waves travel through the medium in the form of crests and troughs.
     - Electromagnetic waves:
  •  These are the disturbance, which does not require any material medium for its propagation and can travel even through vacuum. 
  • Example : Radio waves, light waves etc.