3.2.1 Stationary Waves

• Standing waves are produced by the superposition of two waves of the same frequency and amplitude travelling in opposite directions
• This is usually achieved by a travelling wave and its reflection
  • The superposition produces a wave pattern where the peaks and troughs do not move

• Stationary waves store energy, unlike progressive waves which transfer energy

Formation of a stationary wave on a stretched spring fixed at one end

Comparing Progressive & Stationary Waves

• A stationary wave is made up nodes and antinodes
  • Nodes are regions where there is no vibration
  • Antinodes are regions where the vibrations are at their maximum amplitude

• The nodes and antinodes do not move along the string
  • Nodes are fixed and antinodes only move in the vertical direction

• The phase difference between two points on a stationary wave are either in phase or out of phase
  • Points between nodes are in phase with each other
  • Points that have an odd number of nodes between them are out of phase
  • Points that have an even number of nodes between them are in phase

• The image below shows the nodes and antinodes on a snapshot of a stationary wave at a point in time

• • Where:
    • L is the length of the string
    • One wavelength λ is only a portion of the length of the string

ANSWER: C