Determination of e/m

Complete Fine Beam e/m system

Using the gas filled tube, the deflection of electron beams in a uniform magnetic field (with the use of Helmholtz coils) provides a means of quantitatively determining the charge-to-mass ratio of the electron, e/m.

The tube’s n electron beam system consists of an indirectly heated oxide cathode, a Wehnelt cylinder and a perforated anode, in neon residual gas at a precisely set pressure. Integrated measurement marks for parallax-free determination of the diameter of the fine beam is also part of the electron beam assembly. Ionization of the gas atoms along the path of the electron produces a sharply defined, visible fluorescent beam. The tube is mounted on a base.

The magnetic field is provided by a set of Helmholtz coils, and the entire system is powered by a single power supply.

TEL-8481SYS3 Complete e/m System with He gas $2,579.00
TEL-8481430NESYS Complete e/m System with Ne gas $2,942.00

Helmholtz Coils

The Helmholtz coils are designed for use with the e/m tube. The coils can be connected in parallel or in series. A spring clip on the top crossbar can be used to mount a Hall sensor for magnetic field measurements.

Coil diameter: 295 mm
Coil spacing: 150 mm
Turns per coil: 124
DC resistance 1.2 Ohms each
Maximum coil current: 5 amps
Weight: 4.1 Kg
TEL 8481500 Helmholtz coils $760.00
Additionally required:
Power Supply TEL-33000
Connecting leads

Replacement e/m tube and base

TThe complete e/m system consists of the TEL-18575 e/m Tube and Base, the TEL 8481500 Helmholtz coils, and the TEL U33000 power supply for the tube and Helmholtz coils.
Gas Helium or Neon
Gas Pressure 1.3X10E-5
Filament voltage 4-14V AC/DC
Filament current: 300-450 mA
Wehnelt voltage: 0 – 50V
Anode voltage: 200-300 V
Anode current \lt;0.3ma
Diameter of fine beam path 20 –120 mm
Division spacing 20 mm
Tube diameter 160 mm
Total height including base 260 mm
Base plate 115X115X35 mm
Weight 820 g
TEL-18575WB e/m tube with base (He gas) $1,060.00
TEL-8481430/Ne e/m tube with base (Ne gas) $1,473.00

Flat Coil in a Rotatable Frame

> In conjunction with the pair of Helmholtz coils (TEL-8481500), this device is intended for experiments involving the law of induction. The flat coil is mounted on a plexiglass frame with a rotary bearing. The electrical connection to the coil is established via sliding contacts. A hand crank and pulley on the rotary frame's axle are used to drive the coil.

Number of turns: 4000
Effective area: 41.7 cm2
Dimensions: 110x80x11 mm
Weight: approx. 360 g
Maximum coil current: 5 amps
Weight: 4.1 Kg
TEL 8481510 Flat Coil in Rotatable Frame $250.00