### Question

Why is that electrons radiate electromagnetic energy when they are accelerated?

An electromagnetic wave, as its name implies, consists of alternating electric and magnetic fields, oriented at 90 degrees to each other, moving at the speed of light. These alternating fields sustain themselves because electricity (moving electric charges) generates a magnetic field, and a changing magnetic field generates an electric field.

To demonstrate the first of these behaviors, hold a magnetic compass near a wire conducting a DC current. The compass needle will orient itself perpendicular to the wire as long as current is flowing. Electric meters and motors both take advantage of this behavior.

To demonstrate the second behavior, plunge a magnet into a coil of wire connected to a current measuring meter. As long as the magnet is moving, current will flow in the coil. Electric generators take advantage of this behavior.

An electron carries an electric charge. A stationary electron creates no magnetic field. (Like a wire with no current). An electron moving at constant velocity generates a steady magnetic field, but (like a stationary magnet in a coil of wire) a constant magnetic field won't result in another electric field. An electron moving with a CHANGING velocity (ie. accelerating), however, generates a CHANGING magnetic field, which WILL produce a changing electric field, which produces a changing magnetic field, etc. In other words, it generates an electromagnetic wave.
Answered by: Paul Walorski, B.A., Part-Time Physics Instructor

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### Science Quote

'When I examine myself and my methods of thought, I come to the conclusion that the gift of fantasy has meant more to me than my talent for absorbing positive knowledge.'

Albert Einstein
(1879-1955)