When a wire under tension is disturbed at a point, waves travel away from the point where the disturbance occurred. The waves are then reflected at the fixed ends of the wire. Therefore, we have two waves of the same frequency travelling in opposite sense along the wire.

Interference occurs between these waves. Points where destructive interference occurs are called nodes or (nodal points). Constructive interference gives anti-nodes.

For certain frequencies of disturbance, the nodes and anti-nodes do not move along the wire. This pattern of stationary nodes and anti-nodes is called a stationary (or standing) wave^*.

When a stationary wave occurs the wire is said to be in resonance.

Stationary waves can occur in other situations; see, for example, "Resonance in Air Columns"

• Waves Chapters Index