Abstract
THE law of the moving-iron instrument has been given in the form, torque equals ½ I2dL/dO, where I is the current in the coil and dL/dO the rate of change of inductance with angular deflexion. This law assumes the current remains constant for a small change in deflexion, but since a change in inductance is produced by a change in current, the assumption does not seem justifiable. The law therefore takes a more complicated form, and in a paper on the subject (J. Inst. Elec. Eng., 90, Pt. II, No. 13, February 1943) Dr. G. F. Tagg describes experiments which show that the simple law does not hold for a simple electromagnetic system, and it is considered that the law as enunciated in most text-books is incorrect.
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LAW OF THE MOVING-IRON ELECTRICAL INSTRUMENT. Nature 151, 423 (1943). https://doi.org/10.1038/151423a0
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DOI: https://doi.org/10.1038/151423a0