Description
In an e/m apparatus, electrons are accelerated through a potential difference. Current flowing through the device's Helmholtz coils produces a magnetic field perpendicular to the direction of the electrons' initial velocities. This produces a force on the electrons, causing them to travel in a curved path. This path becomes visible because the electrons interact with helium gas inside the tube, producing a glow effect as shown below.
Image
The ruler inside the e/m tube can be used to obtain the radius of the electron's circular path. From this the charge-mass ratio of the the electron can be calculated via:
Aliases
e/m Apparatus, Helmholtz Coils, e/m
Preparation Time
1 minute
Equipment Requirements
e/m apparatus, cow magnet
Preparation & Instructions
- Make sure to test the e/m apparatus to ensure it is functioning properly -- select one marked "Good" in the "e/m Apparatus Log
- The room will need to be dark during the demo