What Are Nodes and Antinodes?

Nodes are fixed points in a standing wave where the displacement is always zero. Antinodes are positions where the particles oscillate with the maximum possible amplitude.

This is required at both SL and HL in topic C.4, Standing waves and resonance.

How Nodes and Antinodes Form

A standing wave forms when two identical travelling waves with the same frequency and amplitude move in opposite directions and superpose. At some positions, the waves are always in destructive interference, producing nodes. At other positions, they repeatedly undergo maximum constructive interference, producing antinodes.

Adjacent nodes are separated by $\frac{\lambda}{2}$, and adjacent antinodes are also separated by $\frac{\lambda}{2}$. Therefore, if adjacent nodes are apart, then

$$\frac{\lambda}{2}=0.30\,\text{m}$$

so $\lambda=0.60\,\text{m}$.

All particles between two adjacent nodes oscillate in phase. Particles in neighbouring loops oscillate in antiphase, meaning their phase difference is $\pi$ radians.

A common misconception is that a particle at an antinode remains at maximum displacement. It actually oscillates through the equilibrium position with maximum amplitude. In air columns, also distinguish displacement nodes from pressure nodes: a displacement node corresponds to a pressure antinode, and vice versa.

No net energy is transferred along an ideal standing wave, although individual particles exchange kinetic and potential energy as they oscillate. The amplitude changes continuously with position: it rises from zero at a node to a maximum at an antinode, then falls to zero at the next node.

Exam Technique

In IB questions, identify nodes and antinodes from the standing-wave shape, then use the correct spacing relationship. Label whether the diagram represents displacement or pressure, especially for pipes, and use the term first harmonic rather than “fundamental.”