[UPSC CSE 2003] Electromagnetic Theory (Q398, 20M)

Define Poynting vector and explain its significance. The electric field vector for an electromagnetic field travelling in vacuum is given by \vec{E} = E_0 \cos (kz - \omega t) \hat{i} Calculate the Poynting vector for the wave and show that its magnitude is equal to the energy density of the wave time the velocity of light.