1.4.3 The field of an accelerated charge: Radiation

In the following example a charged particle is shown, which moves with a velocity no far from the speed of light (0.6c), accompanied by a neutral particle with the same velocity.

Something similar to this image will be obtained. A kink in the field lines is observed, corresponding to the division of space into two regions: the inner region, close to a circle, enclosed by the kinks, which contains those points of space that already "know" that the charge has stopped, and the outer region, containing the points where the information has not yet arrived. The field lines in the outer region (look at the red arrows) point towards the position where the charge would be found if it had kept moving with the same velocity (which would be the same as the position of the neutral particle, that keeps moving until the simulation is stopped).

A less sharp stop of the charge is shown in the following example.

The result obtained will be similar to that shown in the following figure. A circle centred at the starting point of the charge is plotted in red, and other circle centred at the point where deceleration begins in blue.

Search for an interpretation of the results.

Repeat the previous process but introducing now an acceleration of the charge. To do this, place the slider on the left. The result will be something like that:

Since the particle already had a high velocity, it accelerates up to a velocity very close to the speed of light. The field concentrates in a plane transversal to the direction of the motion of the charge. The field distribution is not radial any more. The radial distribution is therefore a characteristic of charges that move slowly compared to the speed of light.