.sents snapshots of the waves, at successive instants of time, separated
by T /8, where T is the period of the waves. Again the thin continuous curve
represents a wave travelling towards the right and the dotted curve represents a
wave travelling towards the left. (At some instants of time, the incident and reflected
waves lie on top of each other.) These waves are reflected at each of the walls.
Inspection of Figure 6.4 shows that the waves obey the rules of reflection that we