GT4520 electronic specific load (charge-to-mass ratio) tester instruction manual Determination of electron specific charge The electronic specific charge (charge-to-mass ratio, e/m) was first measured by the British physicist JJ Thomson (1856-1940) at the Cavendish Laboratory in Cambridge, England, in 1897 and was therefore awarded in 1906. Nobel Prize in Physics. In physics, there are many experimental methods for determining the electron specific charge, but all of them use an electric field, or a magnetic field, or an electric field and a magnetic field to control the motion of electrons, thereby determining the specific charge of electrons. This experiment was adopted by Helmhol. The magnetic field generated by the coil controls the movement of electrons in the Lorentz tube and determines the electron specific charge. Purpose 1. Observe the deflection of the electron beam under the action of an electric field. 2. Observe the motion law of the motion charge in the magnetic field after the Lorentz force, and deepen the understanding of this. 3. Determine the specific charge of electrons. laboratory apparatus The GT4520 electronic specific load tester includes: Lorentz force tube, Helmholtz coil, power supply and reading scale. The instrument is designed in an integrated design and is installed in a wooden black box for easy observation, measurement, carrying and Storage, as shown in Figure 1. Figure 1 Figure II Figure III 1. Lorentz force tube Lorenz tube, also known as Wilney tube, is the core device of this experimental instrument. It is a large bulb with a diameter of 153mm. After vacuuming in the bubble, it is filled with a certain pressure. The gas bubble is equipped with a special structure electron gun consisting of a hot cathode, a modulating plate, a tapered accelerating anode and a pair of deflecting plates, as shown in Figure 2. The electrons accelerated by the anode pass through the front end of the tapered anode. The holes are ejected to form an electron beam. After the electron beam with a certain energy collides with the inert gas molecules, the inert gas is illuminated, so that the trajectory of the electron beam becomes visible. 2. The Helmholtz coil Helmholtz coil is composed of a pair of circular coils that are uniformly aligned and parallel to each other and coaxial. As shown in Fig. 3, when the two coils are connected in series and connected with a current I, When the distance a is equal to the radius r of the coil, a less uniform uniform magnetic field can be obtained on the axis of the coil. If the distance a between the two coils is not equal to r, the magnetic field on the axis is not uniform. Students can find the total magnetic induction on the Helmholtz coil axis when a=r according to the superposition of the P-point magnetic induction B on the two individual coil axes. B=0.716 μ0NI r Where μ0 is the vacuum permeability, μ0=4π×10-7-H·m-1.N is the number of turns per coil, N=140åŒ.r is the equivalent radius of the Helmholtz coil, r =0.140m. According to the above data, it is calculated B=9.00×10-4/T (1) 3. The front panel of the power supply power supply is shown in Figure 4: Figure 4 The deflection voltage deflection voltage switch is divided into three levels: “uprightâ€, “open†and “downâ€. When “upright†is set, the upper deflection plate is connected with positive voltage, and the lower deflection plate is grounded. When “down†is set, the opposite is true. When “disconnectedâ€, no voltage is applied to the upper and lower deflection plates. When observing and measuring the motion trajectory of the electron beam under the Lorentz force, the “off†position should be set. The deflection voltage is controlled by the deflection voltage switch. The following potentiometer adjustment. The voltage value is from 50~250V, continuously adjustable, no display. The anode voltage is connected to the accelerating electrode in the Lorentz force tube to accelerate the movement speed of the electron. The voltage value is displayed by a digital voltmeter, and the value is adjusted by the potentiometer under the voltmeter. The voltage range during the experiment is about 100~ 200V. The coil current coil current (excitation current) direction switch is divided into three steps: “shunâ€, “off†and “reverse timeâ€. When “shunâ€, the current direction in the coil is clockwise, and the clockwise indication on the coil When the light is on, the direction of the generated magnetic field is directed to the inside of the machine. When the "reverse time" is set, the opposite is true. When "off" is set, the current direction indicator on the coil is completely extinguished, and there is no current in the coil. The current value is indicated by the digital ammeter. Size, adjusted by the potentiometer below the ammeter. Please note: Before converting the direction of the coil current, the coil current value should be adjusted to the minimum to avoid the contact point of the strong arc burnout switch when the current direction is switched. When observing the deflection of the electron beam under the action of the electric field force, the switch should be set to the "off" position. An external ammeter and an external voltmeter terminal are provided on the back cover of the instrument for external large-scale voltmeter and ammeter when used for classroom demonstration. The reading device is equipped with a single-claw digital vernier and a mirror on the front and rear coils of the Helmholtz coil, so that the claws, electron beam trajectories and claws on the vernier are mirrored when measuring the diameter D of the circumference of the electron beam. The three images in the coincidence form a line to reduce the parallax and improve the accuracy of the reading. The cursor reading is divided into two sizes: inch and mm. Please use the mm scale. Experimental principle For an electron moving at a velocity Ï… in a uniform magnetic field B, it will be subjected to the Lorentz force F=e×υ×B. When Ï… and B are in the same direction, the force F is equal to zero, and the motion of the electron is not affected by the magnetic field. When Ï… and B are perpendicular, the force F is perpendicular to the velocity Ï… and the magnetic induction B, and the electrons move in a uniform circular motion in a plane perpendicular to B, as shown in Figure 5. Maintaining the electron F=eÏ…B=m Î¥2 R e = Ï… (2) m RB The force of the circular motion is the Lorentz force, where R is the radius of the electron motion orbit. It can be seen that in the experiment, as long as the velocity Ï… of the electron motion, the radius R of the orbit and the magnetic induction B are measured, the specific charge of the electron can be determined. The speed of the electron motion should be determined by the accelerating electrode, that is, the voltage U of the anode (the initial velocity when the electron leaves the cathode is relatively small and can be ignored). 1 MÏ…2=eU (3) 2 Substituting (3) into (2), e = 2U m B2R2 Figure 5 Substituting (1) into the above formula, the electron specific charge e =2.47×106 U c?kg-1 m R2I2 If expressed by the diameter D of the electron beam trajectory, then e =9.88×106 U c?kg-1 (4) m D2I2 In the formula, U, D, and I are all quantities that can be measured experimentally. From this, the electronic specific charge can be obtained. If the speed of the electron motion and the magnetic induction B are not completely perpendicular, the electron beam will make a spiral motion. Experimental content Before starting the power-on experiment, check that the control switches and knobs on the instrument panel should be placed in the following position: the deflection voltage switch is “offâ€, the potentiometer is turned counterclockwise to the minimum voltage (50V, no display). Adjust the anode voltage The potentiometer is also turned counterclockwise to zero. The coil current direction switch is set to "off", and the potentiometer for adjusting the coil current is also adjusted counterclockwise to zero. The purpose of the above adjustment is to protect the instrument from high current and high voltage. Impact. Extend the service life of the Lorentz tube. Turn on the power, preheat for 5 minutes. Gradually increase the anode voltage to about 100~200V, you can see a beam of pale blue green light from the electron gun, this is the electron beam. 1. Observe the deflection of the electron beam under the action of an electric field Rotate the Lorentz force tube so that the angle is indicated as 90o, that is, the electron beam points to the left and is perpendicular to the coil axis. When turning the Lorentz force tube, be sure to hold the bakelite tube holder by hand, and do not hold the glass bulb to rotate. So as not to loosen the seat. Turn the deflection voltage switch to the "upward" position. At this time, the upper deflection plate is positive, the lower deflection plate is grounded, and the deflection direction of the electron beam is observed. The deflection voltage on the deflection plate is increased to observe the change of the deflection angle. When the voltage is constant, increase the anode voltage and observe the change of the deflection angle. Then adjust the deflection voltage to the minimum and the deflection switch to the "down" position for the same observation. Record observed phenomena and make theoretical explanations. 2. Observe the trajectory of the electron beam in the magnetic field. Turn the deflection voltage switch to the “off†position. The coil current direction switch is turned to the “positive†position. The current on the coil is illuminated by the direction indicator. The coil current and the anode voltage are increased to observe the movement of the electron beam in the magnetic field. Change situation. Turn the Lorentz force tube for further observation. Record observed phenomena and make theoretical explanations. 3. Measuring the specific charge of electrons According to the above, the electron beam trajectory is adjusted to a closed circle. Using the reading device, the diameter of the electron beam trajectory is carefully measured under different anode voltages U and different coil currents I. Calculate the electron according to formula (4) Bihe. Specific content suggestions: 1) Fix the anode voltage, change the coil current, and make multiple measurements. 2) Fix the coil current, change the anode voltage, and make multiple measurements. In order to make the experimental results more accurate, the key is to measure the diameter of the electron beam trajectory. D. The diameter of the circle is suitable between 4cm and 9cm. After the end of the experiment, the anode voltage and coil current are adjusted to a minimum, and both the deflection voltage switch and the coil current switch are turned to the "off" position, and then the power is turned off. Data table Students take care of themselves. Thinking problem 1. Why is the electron beam in the process of rotation, the trajectory becomes thicker and thicker, and it is more and more blurred. Is this normal? Please make a theoretical analysis. 2. Try to discuss from the measurement error point. The grading value of the vernier scale used in the reading device is 0.01mm. Is it reasonable? why? How much more should the indexing value be more reasonable? GT4520 electronic specific load tester instructions Overview The model of the GT4520 electronic load cell tester is model 153W-2 Lorentz force demonstrator, which has been used for more than 20 years. Now the company has improved on the original 153W-2 instrument, which can be used for measurement at the same time. Electronic specific load and renamed the GT4520 electronic specific load tester. Technical indicators 1, Lorentz force tube diameter 153cm, filled with inert gas, rotation angle >180o, with a scale indication. 2. The equivalent radius of the Helmholtz coil is r=0.140m, the distance a between the coils is equal to the equivalent radius r of the coil, and the number of turns of a single coil is N=140åŒ. 3. The deflection voltage is continuously adjustable from 50~250V, no display. It is divided into “uprightâ€, “disconnected†and “downâ€. The anode voltage is continuously adjustable from 0 to 250V. The voltage value is digitally displayed with an error of ±0.5%. The coil current is 0~2A continuously adjustable. The current value is digitally displayed, the error is ±0.5%. It is divided into three levels: “shunâ€, “disconnect†and “reverse timeâ€. There is an indicator light indicating the current direction. 4, the average relative error E ≤ 5%. Instrument acceptance 1. According to the packing list, please click on the complete set of instruments. 1GT4520 electronic specific load tester (host) 2 Lorentz force a 3 power cord 4 experimental lectures. 2, visual inspection. Is there any damage caused by rough handling? 3. Screw the fixing screw at one end of the downstream scale and lower the vernier scale. Then insert the Lorentz force tube into the main unit. Pay attention to the hand-held tube bakelite tube (do not grab the glass bulb) when inserting the tube, and connect the bakelite tube to the key. The socket key on the quasi-host should not be hard-inserted to avoid inserting the wrong pin and burning the Lorentz force tube. Fix the vernier. 4. Before starting to switch on the electric current, check the position of each control switch and knob on the instrument panel. It should be in the following position: the deflection voltage switch is set to “offâ€, and the potentiometer is turned counterclockwise to the minimum voltage (50V, no Display) Adjust the potential of the anode voltage counterclockwise to zero. The coil current direction switch is set to “shunâ€, and the potentiometer for adjusting the coil current is also turned counterclockwise to zero. Turn on the power and warm up for 5 minutes. Gradually increase the anode voltage. Up to 100∽200V, you can see a beam of pale blue green light emitted from the electron gun. This is the electron beam. Change the voltage of the deflection electrode and adjust the current of the coil to observe the orbit of the electron beam. When adjusting the coil current The deflection voltage switch should be set to "off". 5. Turn down the anode voltage and coil current, then turn off the power. Parameter data Measuring formula for measuring electron specific charge e =9.88×106 U c?kg-1 m D2I2 1. Fixed anode voltage and changed coil current Anode voltage U(V) Coil current I(A) Electron beam diameter D(m) Electronic specific load e / m × 1011 (c? kg-1) 100 1.00 0.0739 1.81 1.20 0.0639 1.68 1.40 0.0561 1.66 1.60 0.0476 1.70 1.80 0.0422 1.71 Average value 1.70 2, fixed coil current, change anode voltage Coil current I(A) Anode voltage U(V) Electron beam diameter D(m) Electronic specific load e / m × 1011 (c? kg-1) 1.50 100 0.0510 1.69 110 0.0522 1.61 120 0.0538 1.82 130 0.0576 1.72 140 0.0591 1.76 Average value 1.72 Average relative error E = 2.8% Inflatable Sled,Inflatable Snow Tube,Inflatable Snow Sled,Winter Snow Tube P&D Plastic Manufacture Co., Ltd , https://www.pdinflatable.com