Principle

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 Electric Work Function. It is a very meaningful work to study the escape of electrons. Many electronic devices are related to electron emission. For example, the electron gun of a TV set will affect the quality of the TV set. Therefore, studying the physical properties of this material will improve The performance of the material is very important.

Overview

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 cathode, 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. For the measurement experiment of work function (work function) of metal electrons, basic experimental methods such as Richardson's straight line measurement method, epitaxy measurement method and compensation measurement method are comprehensively applied.There is better skill training in data processing. Therefore, this is a more meaningful experiment.

Features

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 effectively protect 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: The experiment power supply is equipped with two analog data acquisition interfaces, which can be connected to voltage sensors 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

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%

Parts list

Metal Electronic Work Function Tester BEM-5715

Ideal vacuum diode box BEM-5716

Connecting wire, banana plug, 0.8 m, red BC-105084 [2]

Connecting wire, banana plug, 0.8 m, black BC-105083 [2]

Connecting wire, 1m, red BC-105074

Connecting wire, 1m, black BC-105073

Power cord BC-105075

User Manual CD-M-BEX-8509B

Digital experiment options

UI-5400    Capstone data acquisition software

PS-3211    Wireless voltage sensor【2】