Magnetorotation with Alternating Fields of High Frequency

Abstract

SOME time ago we carried out experiments¹ to determine whether the rotation of the plane of polarised light still takes place when the frequency of the magnetic field is very high, for example, ten times that of the Larmor precession frequency. Polarised light from an arc lamp (or preferably a sodium arc) is polarised by a nicol prism, then passes through a tube containing sodium vapour at low pressure (about 7.5 × 10⁴ mm.) and finally is analysed by a second nicol. The tube containing the sodium vapour is placed inside a coil forming part of a resonance circuit tuned to a high frequency valve oscillator. The plane of polarisation of the light was rotated on passing through the sodium vapour in the presence of the oscillatory magnetic field. The intensity of brightness after the second nicol was compared for high frequencies (n) with that for 50 c.p.s. No diminution in this ratio was found when the frequency n was about nine times the Larmor frequency O_L corresponding to the magnetic field amplitude .