. Radio-activity . IZATION THEORY OF GASES [CH. The experimental arrangement used for the electric deflectionof the rays is shown in Fig. 10. The cathode rays are generated at the cathode G, and a narrowpencil of rays is obtained by passing the rays through a perforateddisc AB. The rays then passed midway between two parallelinsulated plates D and E, d centimetres apart, and maintained ata constant difference of potential V. The point of incidence of thepencil of rays was marked by a luminous patch produced on aphosphorescent screen placed at PF. The particle carrying a negative charge e in pa
. Radio-activity . IZATION THEORY OF GASES [CH. The experimental arrangement used for the electric deflectionof the rays is shown in Fig. 10. The cathode rays are generated at the cathode G, and a narrowpencil of rays is obtained by passing the rays through a perforateddisc AB. The rays then passed midway between two parallelinsulated plates D and E, d centimetres apart, and maintained ata constant difference of potential V. The point of incidence of thepencil of rays was marked by a luminous patch produced on aphosphorescent screen placed at PF. The particle carrying a negative charge e in passing between the charged plates, is acted on by a force Xe directed towards the positive Vplate, where X, the strength of the electric field, is given by -^. The application of the electric field thus causes the luminouspatch to move in the direction of the positive plate. If now auniform magnetic field is applied at the plates D and E, perpendi-cular to the pencil of rays, and parallel to the plane of the plates,. Fig. in such a direction that the electric and magnetic forces areopposed to one another, the patch of light can be brought back to itsundisturbed position by adjusting the strength of the magnetic H is the strength of the magnetic field, the force on the particledue to the magnetic field is Heu, and when a balance is obtained Heu = Xe, ^ ..(1). or H Now if the magnetic field H is acting alone, the curvature p of thepath of the rays between the plates can be deduced from thedeflection of the luminous patch. But we have seen that Hp = mu .(2). Il] IONIZATION TIIEOKV OK OASES 75 6 From euuations (1) and (2), the value of u and — for the particle^ m can be determined. The velocity it is not constant, but depends upon thepotential difference between the electrodes, and this in turndepends upon the pressure and nature of the residual gas in thetube. By altering these factors, the cathode particles may be madeto acquire velocities varying between about 1
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