This applet shows interactions between moving charges. It shows with a system of two wires why magnetic fields must exist in order for the postulates of relativity and charge invariance to be consistent with one another.
Wires can have the same current with different drift velocities, in this applet, the electrons are moving at high speeds to show the relativist effects, but the effects are exactly the same at lower speeds.
*This applet is only a representation and approximation.
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