Perform accurate measurements of the charge-to-mass ratio of the electron. Includes power supplies which can also be used in other experiments.
- 1x Helmholtz coils for e/m
- 1x Replacement e/m Tube
- 1x Tunable DC Power Supply (Constant Current)
- 1x DC Power Supply II (Constant Voltage)
- 1x Red and Black Patch Cords
See the Buying Guide for this item's required, recommended, and additional accessories.
In 1897, J. J. Thomson showed that the mysterious cathode rays were actually negatively charged particles—he had discovered the electron. In the same year he measured the charge-to-mass ratio of the electron, providing the first measurement of one of the fundamental constants of the universe.
The Charge-to-Mass Ratio System reproduces one version of Thomson’s landmark experiment, providing an accurate measurement of the charge-to-mass ratio of the electron. And, since the electron tube can be rotated through 90°, students can also make a more general study of the behavior of electrons in a magnetic field.
This apparatus also has deflection plates, so students can study the effect of an electric field on moving electrons.
How It Works
A large, helium-filled electron tube is mounted between a pair of Helmholtz coils. The tube contains an electron gun, which generates a focused beam of electrons. A measured current is applied to the Helmholtz coils so that the magnitude of the magnetic field within the electron tube can be calculated. A measured accelerating potential (V) is then applied to the electron gun. The magnetic field (B) deflects the electron beam in a circular path with a radius (r) that is measured using the illuminated mm scale. From these measured values, the charge-to-mass ratio of the electron is calculated: e/m = 2V/B2r2. (The details of the calculations are fully described in the manual.)
|Hemholtz Coil Radius||16 cm|
|Number of Turns||130|
|Maximum Current||3.5 A|
|Filament Voltage||6.3 VAC|
|Acceleration Voltage||0 - 200 V|
|Tube Diameter||15.5 cm|
|Parts Available Separately||P/N||Price|
|Helmholtz coils for e/m||SE-9626||$1,030|
|Tunable DC Power Supply (Constant Current)||SE-9622||$927|
|DC Power Supply II (Constant Voltage)||SE-9644||$1,030|
|Replacement e/m Tube||SE-9651||$720|
|Replacement Mirror Scale -- e/m Apparatus||SE-9649||$61|
|Electron Charge to Mass Ratio||English||3.04 MB|