M. Fabbrichesi , SISSA

Radiation from an oscillating charge distribution

In the begining of this lesson, corrections to the potentials Φ and **A **are derived leading to the so-called retarded potentials ( Liénard-Wiechert potentials ) where it is taken into account that a signal takes a finite time, corresponding to the velocity of light, to propagate from the source point of the field to the observation point **r. **Next, the problem of the radiation from an oscillating charge distribution is considered. Solutions for the vector potential are found for both the *near zone *and *far zone*. For the latter it is shown that the leading term of the vector potential depends on the electric dipole moment * p*. Expressions for the fields

**E**,

**H**and for the power radiated per unit solid angle are then given [Jackson, sec. 14.3]. In the last part of the lesson it is shown how by starting from the definition of dipole and by using the Liénard-Wiechert potentials it is possible to come to the result previously found for the radiated power (Hertz oscillator).