Lecture 4 : Energy in electric and magnetic fields
3. Energy of EM waves (contd..)
Energy density stored in EM fields
We have already seen that the energy stored in electric field is
(we showed this result for a static field). When
the electric field represents a propagating wave, then taking into
account the "factor of 2" for averaged quadratic quantities, we get
(20)
The energy stored in magnetic field is (we
showed it for a static magnetic field). For a propagating wave,
Including the "factor of 2", we get
(21)
For a plane EM wave, energy stored in electric and magnetic
field is equal. The total energy of an EM wave is
(we showed this result for a static field). When
the electric field represents a propagating wave, then taking into
account the "factor of 2" for averaged quadratic quantities, we get
(we
showed it for a static magnetic field). For a propagating wave,
Including the "factor of 2", we get
