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:
- On the basis of Medium of Propagation
- Mechanical waves or Elastic Waves
- Non-mechanical waves or Electromagnetic waves.
- On the basis of Direction of Propagation
- Transverse waves
- 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. |