For a spherically symmetric medium, the wave equation in spherical coordinates can be written 128 (2) eik(-u) ,2 Show that a solution is of the form u for the r dr as: 1 du du )= dr v dt outgoing wave. Note that the dependence of amplitudes for a spherical wave can also be shown through considerations of energy over a spherical surface where energy is proportional to the square of the wave amplitude.