The orbit of a charged particle in a uniform and constant magnetic field is a circle when the initial velocity of the particle is perpendicular to the magnetic field. The radius of the orbit depends on the charge to mass ratio of the particle, q/m, the speed of the particle v, and the strength of the magnetic field B. When the strength of the magnetic field and the initial speed of the particle are known, a measurement of a radius of the orbit determines q/m. This principle was used by J.J.

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... son to measure the charge to mass ratio of the electron, e/m, in 1897. In this experiment I have used a commercially available CRT-8SJ31J with 70mm diameter screen size to repeat the Thomson's experiment and determine e/m of the charged particles. Electronic charge to mass ratio (e/m) is determined by subjecting the electron beam to electric and magnetic fields. This experiment backs up that the measured value of charge to mass ratio is in close agreement with the standard value of this ratio.