Adjoining figure shows the snapshot of two waves A and B at any time t. The equation for A is y=Asin(kx−ωt−ϕ), and for B it is y = A sin (kx−ωt). It is clearly shown in the figure that wave A is ahead of B by a distance ϕk.
The motion of a single point in time, i.e., y versus t for two waves is best represented by