When and Where is a Current Electrically Neutral?
Thomas E. Phipps
Many textbooks of electromagnetism give an example in which a current-carrying wire is alleged to be electrically neutral when at rest in the laboratory. They then show that the Lorentz contraction of moving charge, demanded by special relativity theory, causes a bunching of positive charge and a thinning of negative charge in the inertial system co-moving with the conduction electrons, with a resulting charge density imbalance and non-vanishing electric field measurable in that system. By a more careful application of special relativity theory, we show, on the contrary, that the wire cannot be strictly neutral in its rest system. Therefore the textbook calculations are in error.
