1 What is EM radiation EM field is excited by time-dependent charge and currents. It may propagate in form of waves The problem is usually solved in terms of potentials 特征:与1/r正比的电磁场! 2. It is a boundary value problem Source charge and current excites EMF, EMF in turn affects source distribution -- boundary value problem For convenience our discussions are limited to a simple case Distribution of source is known1. What is EM radiation EM field is excited by time-dependent charge and currents. It may propagate in form of waves. The problem is usually solved in terms of potentials. 2．It is a boundary value problem Source (charge and current) excites EMF, EMF in turn affects source distribution --- boundary value problem! For convenience, our discussions are limited to a simple case – Distribution of source is known. 特征：与1/r 正比的电磁场！