Waves (in general)
E = Eo sin(?) where ? is a phase angle
in a moving wave, ? changes with both
- time (goes 2? radians in time T) and
- distance (goes 2? radians in distance ?)
so ??= (2?/?)*x +/- (2?/T)*t
- where 2?/T = ? and
- where 2?/? = k and so
phase speed: v = distance/time = ?/T = ?f = ?/k