Thomson e/m Tube
Thomson e/m Tube
TEL-2525
The Thomson e/m Tube is an evacuated tube in which a scale is printed on one side of a semitransparent square mica card. This card is held in place by two metal plates which can provide an Electric Field, E. Helmholtz Coils held in place by the Universal Stand can then provide a Magnetic Field, B at right angles to the Electric Field. A phosphor on the opposite side of the mica card will show the parabolic path of the electron beam in an Electric Field and the circular path of the beam in a Magnetic Field.
TEL-2525
The Thomson e/m Tube is an evacuated tube in which a scale is printed on one side of a semitransparent square mica card. This card is held in place by two metal plates which can provide an Electric Field, E. Helmholtz Coils held in place by the Universal Stand can then provide a Magnetic Field, B at right angles to the Electric Field. A phosphor on the opposite side of the mica card will show the parabolic path of the electron beam in an Electric Field and the circular path of the beam in a Magnetic Field.
A beam of electrons is generated from a hot filament. This beam is accelerated through the Magnetic and Electric Fields which are at right angles to each other and in a path that is perpendicular to the Electric Field. Using the kinetic energy formula 1/2mv2 and the Lorentz equation F=eE+evXB, (which describes the force on a charged particle in a Magnetic and Electric Field), permits one to calculate e/m. You can determine e/m using Thomson's method. You can also calculate e/m by using just the Magnetic Field.