
 Wave Functions 
  In fact, most physical waves, such as those of sound in air or waves on the surface of water, or an electromagnetic wave moving along a transmission line, or light propagating down a fibre, are not precisely described by an equation of this type. 
  This is quite accurately true for electromagnetic waves, including light, propagating in vacuum, and very close to true for sound waves of low intensity propagating in a homogeneous isotropic medium, for example, which explains the great utility of the simple wave equation. 
  Waves on the surface of deep water are also strongly dispersive, the phase velocity being proportional to the square root of the wavelength. 
 www.du.edu /~jcalvert/waves/wavefun.htm (5715 words) 
