Figure 6.3 Two travelling waves of the same frequency and amplitude travelling in opposite
directions, at successive instants of time. The wave travelling towards the right is represented
by the thin continuous curve and the wave travelling towards the left is represented by the
dotted curve. The thick continuous curve corresponds to the result of summing the two
travelling waves together, i.e. the resultant standing wave. The overall shape of this curve is
just like that of the standing wave corresponding to the fourth harmonic shown in Figure 6.2.
As time increases, the resultant standing wave evolves as shown.