SACE Stage 2 Physics — Electricity & Magnetism 2.4

Thomson's e/m Determination

A simulated Teltron tube. Three controls: the accelerating voltage V_a, the deflecting voltage across the plates V_d, and the magnetic field B in the same region.

Accelerating voltage V_a V

100 V300 V

Deflecting voltage V_d V

−800 V+800 V

Magnetic field B mT

0 mT0.6 mT

Accelerating voltage V_a	— V
Deflecting voltage V_d	— V
Magnetic field B	— mT
Plate separation d	0.040 m
Plate length L	0.080 m

Electron charge e	1.602 × 10⁻¹⁹ C
Electron mass m_e	9.109 × 10⁻³¹ kg
Accepted e/m	1.759 × 10¹¹ C/kg