Experimental decision on the electromagnetic momentum expression for magnetic media

Abstract

An experiment is described which discriminates between the two serious candidates for the correct expression of the electromagnetic momentum density within magnetic media, namely, (1/c2)E*H and epsilon 0E*B. The corresponding predictions of both theories regarding the torques arising on the parts of a capacitor with magnetic material as dielectric are thoroughly examined. Final measurements are reported using three different magnetic samples (ferrites) at approximately 4.2K. The results conclusively expose the inadequacy of the (1/c2)E*H theory and vindicate, within the experimental errors, the Livens proposal (1918), Ge0E*B. A short concluding remark is presented on the linear mechanical momentum balance when uniform Poynting vector is present within a permanent magnet.