e/m Thomson Method Apparatus

Apparatus

The experimental setup for Thomson’s method consists of the following components:

1. Electron Gun (Electron Source)

   • A heated filament (cathode) emits electrons via thermionic emission.
   • A cylindrical anode accelerates the electrons by applying a known potential difference ($V$).
   • The emitted electrons form a narrow beam.

2. Electric Deflection Plates

   • A pair of parallel plates produces a uniform electric field ($E$) perpendicular to the electron beam.
   • The potential difference applied across the plates (VEV_EVE​) causes vertical deflection of the electron beam.

3. Magnetic Field (Helmholtz Coils)

   • A pair of Helmholtz coils generates a uniform magnetic field ($B$) perpendicular to both the beam and the electric field.
   • The field is controlled by varying the current ($I$) through the coils.

4. Fluorescent Screen / Photographic Plate

   • The electron beam impacts a fluorescent screen, producing a visible spot that allows measurement of beam deflection.

5. Power Supplies

   • High voltage power supply for the electron gun (accelerating voltage $V$).
   • Variable voltage supply for the deflection plates.
   • Current supply for the Helmholtz coils.

6. Measurement Scale

   • A scale is used to measure the displacement of the electron beam on the screen.