An oscillating quantity a can be written as a=ao cos(wt), where ao is the amplitude, w is the angular fre- quency, f=w/2T is the frequency, and T=1/f is the period a plane wave a=a(t-a/v) travelling along the z-axis can be written as a= ao coslw(t The quantity w(t-v in the bracket is the phase The wave is also unattenuated since ao is a constant