BEX-8510 · Ideal vacuum diode comprehensive experiment 
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There are a lot of free electrons in the metal, but the energy of the electron inside the metal is lower than the energy outside. Therefore, when the electron escapes from the metal, it needs to provide some energy to the electron. This energy is called the electron work   function. Studying the escape of electrons is a very meaningful work. Many electronic devices are related to electron emission. Therefore, studying the physical properties of this material is very important to improve the performance of the material. In addition, this   experiment can also use the magnetron method to measure the electron charge-to-mass ratio, and study the electron energy in vacuum

to follow the Fermi-Dirac distribution.


The core components of this experimental device are an ideal (vacuum) diode and an energized solenoid coil wrapped around the ideal diode. In this experiment, by measuring the electron work function of tungsten metal, tungsten wire is used as the "ideal" diode cathode material, the anode is made into a cylinder coaxial with the   athode, and the cathode emission surface is limited to a certain length with uniform temperature and can be approximated Think of the electrode as an ideal state of infinite length without edge effects. The determination of the work function (work function) of electrons and the experiment of the electron-to-mass ratio have comprehensively applied the basic methods of Richardson linear measurement, epitaxy measurement, compensation measurement and magnetron control. There is better skill training in data processing. Therefore, this is a more meaningful experiment.


  1. Independent ideal vacuum diode seat: The ideal vacuum diode is inserted on the independent tube seat, and is equipped with a   transparent acrylic protective cover, which can not only intuitively observe the working state of the vacuum diode, but also effectivelyprotect the glass device. The independent tube base is engraved with a clear experimental schematic diagram, which can enable   students to better understand the entire experimental principle.


  2. Accurate anode current measurement module: the anode current measurement module uses a micro-amp current amplifier and a   four and a half digital display meter, with a measurement range of up to 0.1uA~20mA, which can measure weak anode current   accurately, finely and stably.

  3. Stable anode voltage output module: the anode voltage output uses a linear power supply, and the output amplitude reaches   0~160.0V, which can provide the anode voltage of the vacuum diode stably and efficiently.

  4. Convenient data acquisition interface: Each experiment power supply is equipped with an analog data acquisition interface, which canbe connected to a voltage sensor and PASCO data acquisition software, which can collect a large amount of data in real time to   analyze the test results, and complete the experiment content conveniently, quickly, and efficiently.


Experimental content and typical data

Experiment 1: Determination of work function of metal electron

Table 1: Anode current and its logarithmic value at different anode voltages and filament temperatures, graph lgIa~√Ua,   get the intercept lgI at different temperatures and fill in Table 2.

Table 2: The calculated values of  lg( I / T2) and  1/T  at different temperatures T

Make a graph of lg( I / T2) ~ 1/T according to Table 2 and find the slope m of the line

Slope of straight line: m = -22802

Escape potential: φ = 4.53 (V)

Work function (work function) eφ = 4.53 eV

Relative error compared with the recognized value of work function (work function)  eφ=4.54eV : Er = 0.33%

Experiment 2: Electron movement in radial electric field and axial magnetic field (Magnetron method measures electron charge-to-mass ratio)

Experiment 3: Research on Fermi-Dirac distribution




Parts list

Metal Electronic Work Function Tester BEM-5715

Adjustable DC (constant voltage and constant current) power supply I, 12V/1A BEM-5055

Ideal vacuum diode box BEM-5716

Solenoid coil BC-105236

Connecting wire, 2mm sheathed banana plug, red BC-105238 【2】

Connection wire, 2mm sheathed banana plug, black BC-105239 【2】

Connecting wire, 4mm banana plug, red BC-105084

Connecting wire, 4mm banana plug, black BC-105083

Connecting wire, 4mm sheathed banana plug 1m, red BC-105074

Connecting wire, 4mm sheathed banana plug 1m, black BC-105073

Power cord BC-105075

User Manual CD-M-BEX-8510B

Digital experiment options

UI-5400    Capstone data acquisition software

PS-3211   Wireless voltage sensor【2】

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