e/m Apparatus

Using the e/m Apparatus is a great way to demonstrate Lorentz Force!

Designed to be compact, this e/m Apparatus (also commonly known as a “Lorentz Force Demonstrator”) clearly demonstrates that electric and magnetic fields bend moving charges. This bundle includes the necessary power supply for this classic experiment. Use it to show magnetic and electrostatic deflection, measure e/m, and investigate electron beam behavior.

How it works: The e/m Apparatus (with power supply) consists of a vacuum tube mounted inside a pair of Helmholtz Coils that provide a transverse magnetic field. An electron gun placed inside the tube points downward and generates a beam of electrons controlled by adjusting the Accelerating Voltage knob. The magnetic field inside the tube is controlled by adjusting the Coil Current knob. Electrons are bent into a circle in accordance with the Lorentz Force Law qv x B. This beam is made visible by placing a small quantity of helium gas at low pressure in the vacuum tube; the helium glows when struck by the electrons.

The ratio of charge over mass for an electron can be calculated using the diameter of the circular path, the current applied to the Helmholtz coils, and the voltage used to accelerate the electrons. The accelerating voltage can be varied from 100 to 500 VDC and the current varied from 0-3A DC to provide a wide variety of beam energies and deflection fields. The orbit diameter itself is measured on an internal glass scale that includes fluorescent marks for easy measurement. The mark glows when the beam strikes it, making it easy to determine the exact beam diameter. Accelerating voltage and deflection current values are displayed on three-digit panel meters that allow quick and precise measurements. The voltage and current power supplies are controlled by an onboard microprocessor to ensure stable, precise, and easily reproduced results. Comes completely assembled with the electron tube, Helmholtz coils, an integral current and voltage power supply and complete usage manual.