1.1 Short Notes: Understanding Waves

Wave Motion

  • A wave is a travelling disturbance from a vibrating source.
  • In Figure 1.1, when a drop of water hits the surface of the water, it creates a disturbance causing a wave to move outwards.
  • When there is a disturbance on the water surface, this will cause wave to be formed. This disturbance causes the particle to vibrate. Therefore, energy is transferred outward by the wave without transferring matter.

Types of Waves

Transverse wave

  • The direction of vibration is perpendicular to the direction of motion of the wave.
  • Examples of transverse wave are radio waves, water waves, ultraviolet and infrared.

Longitudinal wave

  • The direction of vibration is parallel to the direction of motion.
  • Examples of longitudinal wave is sound wave.

Displacement - Distance Graph

  • In Figure 1.4, the crest is the highest point on a wave.
  • The trough is the lowest point on a wave.
  • The amplitude is the maximum displacement of the wave from its equilibrium position.
  • Wavelength, λ is the distance between two successive crest or trough.

Displacement – Time Graph

  • The period, T is the time taken for the wave to complete one oscillation.
  • The frequency, f is the number of oscillations in one second.

Relationship between speed, wavelength and frequency

The wave in Figure 1.6 is propagating with a frequency of 15 Hz. The wavelength of the wave is 3 cm. What is the speed of the wave?


Example question

Determine the velocity of the wave when the displacement of the particle is at maximum.


Velocity = Displacement/Time

= 4 cm/ 1 s

= 4 cm/s


  • What are the types of wave?
  • What is the relationship between time period and frequency?
  • A wave is travelling with a frequency of 20 Hz. Find the velocity of the wave.


  • Transverse wave and longitudinal wave.
  • Frequency is inversely proportional to period.
  • 80 cm/s.