Skip to main content

Class 9, Science, Chapter-11, Lecture-1, Waves (Notes)

WAVE MOTION:

The motion of the disturbance produced in one part to another part without involving transfer of material with it is termed as wave motion.
Examples: motion of sound, motion of water waves (ripples)

WAVE:

A vibratory disturbance in a medium which carries energy from one part to another without involving transfer of material is termed as wave.
Examples: sound wave, water wave, light wave.

RIPPLES:

Waves on water surface with small distance between concentric rings are called ripples.

Characteristics of Wave Motion:

  • Wave motion is a periodic disturbance travelling in a medium.
  • Particles of medium vibrate about fixed positions, they do not move.
  • It travels at the same speed in all directions.
  • It only transfers energy from one point to another. It does not transfer matter.
  • The velocity of wave motion depends only on the nature of the medium and not on the nature or motion of the source.

Types of Waves:

  1. On the basis of Medium of Propagation
    1. Mechanical waves or Elastic Waves
    2. Non-mechanical waves or Electromagnetic waves.
  2. On the basis of Direction of Propagation
    1. Transverse waves
    2. Longitudinal waves

MECHANICAL WAVES:

The waves which require a material medium to propagate are called mechanical waves or elastic waves.
Examples: Sound wave, Water wave

NON-MECHANICAL WAVES:

The waves which do not require a material medium to propagate are called non-mechanical waves or electromagnetic waves.
Examples: Light wave, Radio wave

Differences Between:

Elastic Wave

Electromagnetic Wave

1. Require a material medium

1. Do not require a material medium

2. Have low speed

2. Have very high speed of 3 x 108 m/s.

3. Low frequency and large wavelength

3. High frequency and short wavelength

4. These are due to the vibration of the particles of the medium.

4. These are due to the variation in the electric and magnetic fields in space.

5. Can be transverse or longitudinal.

5. Can only be transverse.

TRANSVERSE WAVES:

The waves in which the particles of the medium move perpendicular to the direction of motion of the wave are called transverse waves.
Examples: Light wave, Water wave

CREST: 

The point on a transverse wave that exhibits the maximum amount of positive or upward displacement from the line of zero disturbance is termed as crest.

TROUGH: 

The point on a transverse wave that exhibits the maximum amount of negative or downward displacement from the line of zero disturbance is termed as trough.

LONGITUDINAL WAVES:

The waves in which the particles of the medium move along the direction of motion of the wave are called longitudinal waves.
Examples: Sound Waves 

COMPRESSION: 

The point on a longitudinal wave that exhibits the maximum density of the medium is termed as compression.

RAREFACTION: 

The point on a longitudinal wave that exhibits the minimum density of the medium is termed as rarefaction.

Differences Between:

Transverse Wave

Longitudinal Wave

1. The particle of the medium vibrate at right angle to the direction of wave.

1. The particles of the medium vibrate parallel to the direction of wave.

2. These consist of CREST and TROUGH

2. These consist of COMPRESSION and RAREFACTION.

3. Can be propagated only through solid or over the surface of a liquid.

3. Can be propagated through solid, liquid, gas.

4. These can be POLARIZED (directed in one direction).

4. These can not be POLARIZED.