Poynting vector and intensity It can be shown that the Poynting vector always has the same direction as the ray. For a spherical wave this can be shown easily: 2 2n 下=ri Therefore: e.m.power propagates along rays! radiation Power-Density or Intensity is defined as: 1闷=S= 2n Poynting vector and intensity It can be shown that the Poynting vector always has the same direction as the ray. For a spherical wave this can be shown easily: S = E × H * 2 = E 2 2η ˆ ir Therefore: e.m. power propagates along rays! radiation Power-Density or Intensity is defined as: S = S = E 2 2η Tx r = rˆ ir