A new method for measuring electrical resistivities

Abstract

A new method for the measurement of electrical resistivities of conductors has recently been developed in this laboratory by inducing a momentary electromotive force in a plane uniform ring of the conductor suitably suspended in a homogeneous magnetic field and observing the resultant ballistic throw. In the actual experiments, the field was horizontal and the ring was suspended from a torsion fibre with its plane vertical and with its axis at an angle of 45° to the direction of the field. When the field is switched off in an interval of time very small compared to the time-period of the suspension, the ballistic kick θ is given by ° = A²TH²a/8πIρLin which I is the moment of inertia and T the period of oscillation of the suspension, A is the area of the ring, a the area of its cross-section and L its circumference, H is the magnetic field, and ρ is the resistivity. (The effect of the field on the resistivity is ordinarily negligible.