E/M Ration Experiment

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Experiment #9: e/m Ratio Submitted by: Linda Agaby 1255497 Alexandre Belisle 1236050 Instructor: Caroline Viger Experiment performed: May 03, 2013 Report submitted: May 10, 2013 Abstract J.J. Thompson first discovered the charge to mass ratio of the electron by measuring the deflection of electrons when accelerated in a magnetic field, and their kinetic energy. To reproduce this experiment, Helmholtz coils were used to create a magnetic field, and an electron gun was used to create a flow of electrons. The electron gun is composed of a filament, and when the filament is heated, electrons obtain enough energy to escape the metal. These electrons are then accelerated by a potential between the anode and the cathode that is varied during the experiment. The electrons experience a magnetic force due to the field that is perpendicular to the velocity vector, so the electrons follow a circular path. By measuring the radius of the circular electron beam, the acceleration voltage and the current supplied, we can determine the charge to mass ratio. The value obtained was 1.00E11C/kg, which has a 30.65% percent deviation from the theoretical value. Introduction Velocity Vector Velocity Vector r r Electron Gun Voltage Controller Electron Gun Voltage Controller B B ΔV ΔV -Explanation: An electron is being shot by an electron gun/cathode gun. The electron is accelerating by being repelled by a negative plate and attracted by a positive plate. After, the electron is being accelerated in the y-axis (deflected) by a positive and a negative deflective plate. Afterward, the electron keeps his elliptical/circle path because of a magnetic field (out of the page) created by a Helmholtz coil. -Proof that: em=2VB2r2 F=ma It is well known that a particle following a circular orbit must have an acceleration

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