Abstract
IN a recent experiment1 a disk of high dielectric constant material (barium titanate) was suspended as a torsional pendulum in an intense axial magnetic field. It was found that if a radial electric field was applied to the disk in time quadrature with the magnetic field a substantial torque was produced which, to within experimental accuracy (<5%), was in agreement with a force density Ṗ×μ0H in the disk. The surprising feature of the torque was that it had a time average, contradicting the ‘Abraham force’ which predicts a force density of ∂(P×μ0H)/∂t with zero time average. The experiment seemed to suggest that the quantity Ṗ×μ0H does not produce a force since its time average would be equal but of opposite sign to the time average of Ṗ×μ0Ḣ.
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Walker, G. B., and Walker, G., Nature, 263, 401 (1976).
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WALKER, G., WALKER, G. An unusual electromagnetic surface force. Nature 265, 324 (1977). https://doi.org/10.1038/265324a0
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DOI: https://doi.org/10.1038/265324a0
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