MadSci Network: Physics

Re: Why is radiation caused by acceleration decelerati

Date: Sat Nov 15 10:42:40 2003
Posted By: Yaxun Liu, Grad student, Electrical and Computer Engineering, University of Waterloo
Area of science: Physics
ID: 1068355943.Ph

Radiation means you have certain far field behavior. Generally, electric 
and magnetic field are in phase but perpendicular to each other, and 
attenuate inverse proportionally to the distance. Therefore to determine 
whether there is radiation, you only need to calculate the far field.

There is a derivation of the far field of an accelerated particle in the 
following book:

Julian Schwinger etc., Classical Electrodynamics, Ch32.1, Ch32.3, Perseus 
Books, 1998

The main steps of the derivation are as follows:
1) write down the time-domain far field representation of the scalar and 
vector potential for general charge and current distribution

2) derive electric and magnetic far field from scalar and vector potential.
It is found their strength is proportional to an integral, the integrand 
of which is the time-derivative of the delayed current distribution

3) Now consider the special case of a particle. The current distribution 
is a Dirac delta function for the particle. It is found the above integral 
becomes proportional to its acceleration.

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