Here a gaussian pulse of current is placed on a ring. The pulse radiates heavily at first. The current spreads out on the ring becoming a uniform current. At which point the radiation ceases.
This example can explain simple quantum models of atoms. In the Bohr Model of the atom, an electron is treated like a wave on a ring. When the electron forms a standing wave pattern on the ring it forms a stationary current. Only certain discrete orbits satisfy the standing wave condition. Steady currents do not radiate because it takes a changing magnetic field and a changing electric field to create the radiation. For the discrete stationary orbits, no radiation occurs, but when an electron moves from one orbit to another, it is not in a standing wave pattern so it radiates. This simple model explains why discrete orbits exist in which the electron does not radiate, and why the electron radiates when it jumps from one orbit to another.
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