# electric dipole radiation

January 3, 2010

Many undergraduate physics students use David Griffiths’ Introduction to Electrodynamics in their junior level E&M class, and if they make it to Chapter 11, the reader sees how the motion of accelerated charges (in the dipole approximation) can lead to the emission of electromagnetic radiation. However, Griffiths’ derivation of the radiation intensity from an arbitrary dipole source is valid only if the direction of the dipole moment does not change with time. I rederive Griffith’s results without assuming a constant dipole direction to obtain the general formula for the intensity of radiation. I then show how this reduces to Griffith’s earlier expression for the total power radiated. PDF

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