Description

Experiment Topics:
• Electron deflection in a uniform magnetic field
• Closed orbit or spiral path
• Determining an electron's specific charge e/m

This complete experimental system is used to determine an electron's specific charge and investigate the deflection of electron beams in a uniform magnetic field. The system comes complete with a fine-beam tube, Helmholtz coil pair for generating a uniform magnetic field, and operating unit for power supply.

The fine beam tube and Helmholtz coil pair are mounted on the operating unit, the fine beam tube being rotatable around its vertical axis. The tube and coil pair are both connected internally to the operating unit without a need for external wiring. All supply voltages for the tube and the current through the Helmholtz coils are adjustable. The anode voltage and coil current are displayed digitally and can be tapped additionally as equivalent voltage values. Inside the fine beam tube, a sharply delimited electron beam is generated by a system comprising an indirectly heated oxide cathode, perforated anode and Wehnelt cylinder. Impact ionization of neon atoms creates a very bright, also sharply delimited trace of the electron path in the tube. If the tube is aligned optimally and an appropriate current flows through the Helmholtz coils, the electrons are deflected into a circular orbit, whose diameter can be easily determined when the electrons strike one of the equidistant measurement marks, causing its end to light up. Diameter, anode voltage and magnetic field are the parameters used to determine the electron's specific charge. The magnetic field can be calculated from the coil current, the geometry of the Helmholtz coil pair being known.

Fine-beam tube:
Gas filling: Neon
Gas pressure: 1.3x10^-5 hPa
Bulb diameter: 165 mm
Orbit diameter: 20 … 120 mm
Measurement mark spacing: 20 mm
Helmholtz coil pair:
Coil diameter: approx.300 mm
Winding count: 124
Magnetic field: 0 …3.4 mT (0.75 mT/A)
Operating unit:
Coil current: 0 … 4.5 A, 3-figure digital display
Measurement output: 1 V*IB / A
Anode voltage: 15 … 300 V, 3-figure digital display
Measurement output: 0.01*UA
Heating voltage: 5 … 7 V
Wehnelt voltage: 0 … -50 V
General data: Tube's rotary angle: -10° … 270°
Supply voltage: 100 – 240 V, 50/60 Hz
Power supply cable: EU, UK and US
Dimensions: approx.310x275x410 mm³
Weight: approx.7.5 kg

The complete fine-beam tube system consists of the following parts:
Fine Beam Tube T
Operating Unit for Fine-Beam Tube

Spare tube for Fine Beam Tube T: 1008505