# Radiation Pulse from an Accelerated Point Charge

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J. J. Thomson first suggested a pictorial representation of how an instantaneously accelerated point charge can produce a pulse of electromagnetic radiation. An electron, with charge , moving at a constant speed , even when a significant fraction of the speed of light , produces an electric field of magnitude , (add factor if you cannot live without SI units), where represents the *projected* position of the source charge at time , assuming that it continues to move at constant speed from its position at the retarded time . This is derived most lucidly in the Feynman Lectures [1]. Thus a uniformly moving point source emits a spherical longitudinal electric field, although its magnitude does vary with direction. This is represented in the graphic by a series of 12 uniformly spaced radial spokes.

Contributed by: S. M. Blinder (May 2011)

Open content licensed under CC BY-NC-SA

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References

[1] R. P. Feynman, R. B. Leighton, and M. Sands, *The Feynman Lectures on Physics, Vol. II*, Reading, MA: Addison–Wesley, 1964, pp. 26.1–26.4.

[2] E. M. Purcell, *Electricity and Magnetism: Berkeley Physics Course, Vol. 2*, New York: McGraw-Hill, 1984, pp. 331–334.

[3] D. V. Schroeder, "Purcell Simplified or Electricity, Magnetism, and Relativity." (January 1999) http://physics.weber.edu/schroeder/mrr/MRRtalk.html.

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