Nodes & Antinodes (DP IB Physics): Revision Note

Nodes & Antinodes

• A standing wave is made up nodes and antinodes

  • Nodes are locations of zero amplitude and they are separated by half a wavelength (λ/2)

  • Antinodes are locations of maximum amplitude

• The nodes and antinodes do not move along the wave

  • Nodes are fixed and antinodes only oscillate in the vertical direction

Nodes and antinodes of a stationary wave of wavelength λ on a string of length L at a point in time 

The Formation of Nodes and Antinodes

• At the nodes:

  • The waves are in anti-phase meaning destructive interference occurs

  • The crest of one wave meets the trough of another

  • This causes the two waves to cancel each other out

• At the antinodes:

  • The waves are in phase meaning constructive interference occurs

  • The crest of one wave meets the crest of another (same for troughs)

  • This causes the waves to add together

Nodes and antinodes are a result of destructive and constructive interference respectively

Phase on a Standing Wave

• Two points on a standing wave are either in phase or in anti-phase

  • Points that have an odd number of nodes between them are in anti-phase

  • Points that have an even number of nodes between them are in phase

  • All points within a "loop" are in phase

Points A, B and D are all in phase. While points A and D are in antiphase with point C

• Constructive and destructive interference can be seen from the phase differences between two waves

A graphical representation of how stationary waves are formed - the black line represents the resulting wave