A Further Study of the Inertia of the Electric Carrier in Copper

Abstract

Nature of the experiments.—An apparatus similar to that of Tolman, Karrer and Guernsey, in which a copper cylinder is oscillated around its axis and the current due to the lag of the electrons in the cylinder detected by means of a secondary of many turns of fine wire connected through an amplifier with a tuned vibration galvanometer, has been used for a further study of the inertia of the electric carrier in metals. The method has been improved, among other ways by arranging to measure the direction, phase, and magnitude of the alternating current produced by the acceleration instead of merely determining the amplitude of the effect, as was done in the earlier experiments. The null method of balancing out the electromotive force of interest, introduced for this purpose, also had the advantage of eliminating the previous uncertain correction for the zero effect. A thorough study of the effect of the earth's field on the moving cylinder was also made, which has not been previously done. Results.—The effect of the earth's field in inducing currents in the moving apparatus was found to be in accord with that theoretically predicted, and it was satisfactorily demonstrated that this effect is eliminated when the cylinder is set parallel to the field and the coil set parallel to the cylinder. The final best value for the electromotive force produced by the acceleration was found to have an amplitude 19% less and a phase lagging 10° behind that predicted on the basis of an elementary theory which assumes a perfectly rigid conductor with conducting electrons having the same mass as electrons in free space. It is not certain whether this discrepancy is due to errors still present in the experimental work, or due to the over simplification introduced in the deduction of the elementary theory. The results are presumably more reliable than those of Tolman, Karrer and Guernsey which gave an amplitude 8% lower than the predicted, using the same apparatus in a less satisfactory form. The results should also be compared with those of Tolman and Stewart who measured the pulse of current produced by suddenly stopping a coil of wire rotating around its axis, and found values about 15% greater than the predicted. A possible source of error in their experiments, due to interaction between metal and insulation, was discovered in the present work, but it may be that there is a real difference in the effective mass of the carrier in the two kinds of experiment. It is believed that the present work demonstrates more satisfactorily than ever before the actual existence of an electromotive force due to the inertia of the electrons in an accelerated metallic conductor.