Bridge measurement of electromagnetic forces

A simple impedance bridge may be used to measure the variation of inductance of a disconnecting switch of practical dimensions as the switch blade is displaced by slight amounts from the closed position. The electromagnetic force tending to open the switch blade, calculated from the observed variation of inductance, checks the theoretical value obtained from Dwight´s formula. The bridge may be used to determine the electromagnetic forces acting on current carrying members the configuration of which is such as to make accurate theoretical calculation impossible.