CHAPTER 14 - Magnetic and Dielectric Measurements

Abstract

This chapter discusses magnetic and dielectric measurements. Magnetic and dielectric materials are widely used in electronics. A practical method of determining the magnetic moment and, hence, the pole strength of a bar magnet is to use a deflection magnetometer. This consists of a long pointer suspended so as to rotate about its center, the angle of rotation being measured by a circular scale calibrated in degrees. Another method of determining magnet moment is to use a vibration magnetometer. The measurement of the real part of relative permittivity is generally performed by measuring the change in capacitance of a capacitor, brought about by the introduction of the dielectric between its electrodes. With a ballistic galvanometer, the damping is small and the pointer oscillates; the flux change must be made very quickly as the periodic time of the galvanometer is only a few seconds. The calibration cannot be made once and for all as it depends on the resistance of the circuit. In Grassot fluxmeter, the damping is very large and the pointer does not oscillate but moves out to the deflected position and stays there.