e/m Experiment - Physics Demonstrations - e/m Experiment | Physics Undergraduate Labs

Filament current must NEVER exceed 4.5 A — this will burn out the electron gun. Always start with filament dial at zero and increase gradually until the beam is visible. Keep emission current at minimum for best results.

Purpose

Electrons accelerated through a known potential are deflected into circular paths by Helmholtz coils, enabling direct measurement of $$e/m$$ . Demonstrates the Lorentz force on moving charges and connects to Thomson's discovery of the electron. This apparatus is currently not functional.

e/m apparatus: large Helmholtz coils on a stand with e/m tube (wrapped in dark shielding) at center, multiple power supplies and meters on a wooden table in a lecture hall

Figure 1: The e/m experiment apparatus with Helmholtz coils, e/m tube, and associated power supplies mounted on a wooden table.

Safety Warnings

Danger: Filament Current Limit

Purpose