Experiment: Deflection of a charged particle and the E/M ratio

Topics covered:

- Electrical deflection

- Determination of the e/m ratio

- Magnetic deflection with Helmholtz coils

Principles and objectives:

The objective of this lab is to carry out magnetic and electrical deflection

of a charged particle.

Magnetic deflection:

Place the coils in the corresponding slots of the tube holder.

Turn on the high voltage power supply. Apply voltage to the coils and observe the beam. The beam follows a circular path, the deflection occurs in a plane that is perpendicular to the magnetic field.

An electron with mass m and charge e, moving perpendicularly to a magnetic field B, is forced to follow a circular path due to the Lorentz force B e v, where v is the electron's velocity and r is the radius

of curvature.

Electrical deflection:

Turn on the high voltage power supply. Activate the capacitor voltage and observe the beam.

An electron, traveling at speed v through the electric field E of a capacitor with plates at voltage UP and with a separation d between the plates,

is deflected along a parabolic path.

Determination of the e/m ratio:

By applying Newton's second law to the electron accelerated by a known electric potential and deflected in a circular manner by a perpendicular magnetic field, it is shown that the electrons undergo an acceleration

ay = eE/m.

- 1 Deflectron (ref 232005) - 1 Set of cables for Deflectron (ref 283598) - 2 High voltage power supplies (ref 281142) - 1 power supply evo 2 F6 / F12 (ref 281483)