Physics Lab Equipment

LEAI-47 Determining Specific Charge of Electron - Advanced Model

LEAI-47 Determining Specific Charge of Electron - Advanced Model


  • Complete apparatus

  • Compact, stable, and affordable

  • Demonstrates electron motion in electromagnetic field

  • Measures e/m and geomagnetic component


This LEAI-47 experiment apparatus is designed to determine the specific charge of an electron, or the electron charge/mass ratio (e/m), to demonstrate the motion properties of electron beam in electrical and magnetic fields, and to measure the geomagnetic component. It is an ideal teaching apparatus for physics laboratories in colleges and universities. This apparatus has the following advantages:

1. Three digital voltmeters for displaying various voltages independently.

2. All parts enclosed in a solid suitcase for convenient maintenance.

3. Three times of electron beam focusing, namely electron spiral motion ≥ 6π.


Using this apparatus, the following experiments can be performed:


1. Quantitatively measure the rules of electron movement in both electric and magnetic field.

    a) Electrical deflection: electron + transversal electric field

    b) Electrical focusing: electron + longitudinal electric field

    c) Magnetic deflection: electron + transversal magnetic field

    d) Spiral motion magnetic focusing: electron + longitudinal magnetic field

2. Determine e/m ratio of an electron and verify the polar coordinate equation of electron spiral motion.

3. Measure geomagnetic component.

The instruction manual contains comprehensive materials including experimental configurations, principles, step-by-step instructions and some experimental results. Please click Experiment Theory and Contents to find more information about this apparatus.



Filamentvoltage 6.3 VAC; current 0.15 A
High voltage UA2600 ~ 1000 V
Deflecting voltage-55 ~ 55 V
Grid voltage UA10 ~ 240 V
Control grid voltage UG0 ~ 50 V
magnetization current

0 - 2.4 A

Solenoid parameters
Longitudinal coil (long)length: 205 mm; inner dia: 90 mm; outer dia: 95 mm; number of turns: 1160
Transversal coil (small)length: 20 mm; inner dia: 60 mm; outer dia: 65 mm; number of turns: 380
Digital meters3-1/2 digits
Sensitivity of electrical deflectionY: ≥0.38 mm/V; X:  ≥0.25 mm/V
Sensitivity of magnetic deflectionY: ≥0.08 mm/mA
e/m measurement error≤5.0%

Parts List

Main unit1
Long coil (solenoid coil)1
Small coil (deflection coil)2
Division screen1
Instructional manual1

     Apparatus for Determining Specific Charge of Electron.png

Schematic diagram of CRT

(Click figure to enlarge)

     Apparatus for Determining Specific Charge of Electron.png

Schematic diagram of front panel

(Click diagram to enlarge)

    LEAI-47 Determining Specific-1.jpg

Spiral trace of electron in magnetic field

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