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1、實驗2: 電子受靜電力及磁力作用的偏折 (課本實驗15/16),陰極射線管CRT的內部結構 控制柵極G 聚焦陽極F 加速陽極A (總電位V1) 水平偏壓(偏折)平行電極板 垂直偏壓(偏折)平行電極板 Z方向無偏折之電子束 螢光幕 陰極射線管(CRT)內的加熱燈絲 陰極射線管(CRT)內的陰極C,目的: 觀察陰極射線管(cathode ray tube, CRT)中之電子束在電場(E)及磁場(B)中之偏折運動情形，並測量電子的荷質比(e/m比) 原理: Lorentz force F = q(E + v x B) SI unit: N = C(V/m) = C(m/s).T,陰極射線管CRT的內
2、部結構,陰極射線管的工作原理 Operation Principle of CRT,I. 在水平和垂直偏折平行電極板(4,5)無外加偏壓信號時： 陰極射線管內的加熱燈絲(8)將陰極C(9)加熱放出熱電子 經控制柵極G(1), 聚焦陽極F(2)及加速陽極A(3)(總電位V1)後 電子往Z方向(6)做等速運動，mvz2/2 = eV1 vz = (2eV1/m)1/2 電子打到螢光幕(XY面)(7)上的中心位置，形成一亮點。,陰極射線管CRT的內部結構,電子質量 m = 9.11 x 10-31 kg 電荷 q = -e = -1.60 x 10-19 C,As V4 = 0 V5 = 0,Com
3、monly used to obtain a visual display of electronic information in oscilloscopes, radar systems, televisions, etc Be a vacuum tube in which a beam of electrons is accelerated and deflected under the influence of electric or magnetic fields.,The electrons are deflected in various directions by two se
4、ts of plates. The placing of charge on the plates creates the electric field between the plates and allows the beam to be steered.,Cathode Ray Tube (CRT),Cathode Ray Tube (CRT) - is one of the main elements of an oscilloscope.,A CRT is commonly used to obtain a visual display of electronic informati
5、on in oscilloscopes, radar systems, televisions, etc. The CRT is a vacuum tube in which a beam of electrons is accelerated and deflected under the influence of electric or magnetic fields. The tubes are produced with electrostatic and electromagnetic control, where electrostatic or magnetic fields d
6、eviate the electron beam respectively. The principle scheme of CRT has electrostatic control as well as the motion of the electrons in the beam drawing a sinusoid on the screen of oscilloscope.,Configuration of CRT,CRT consists of 6 sections: Glass bulb evacuated to a high vacuum (真空管) Cathode (a so
7、urce of electrons，電子槍陰極) Cathode heater (陰極加熱器) Electrodes for brightness and focus control, several accelerating anodes (亮度、聚焦、加速控制柵極) Pairs of horizontal and vertical capacitor plates deviating the electron beam Fluorescing screen (螢光幕),Discharge Tube,It was observed that whenever the glass tube f
8、illed with air at low pressure and sealed with electrodes at both the ends was subjected to about 10,000 volts of electricity, a strange glow was produced around the edges of the wide end of the glass tube, irrespective of the type of gases present in it. The glass tube with sealed electrodes is cal
9、led discharge tube.,Discharge Tube,Electron Gun,Electron guns Electron beams Focusing coils Deflection coils Anode connection Mask for separating beams for red, green, and blue part of displayed image Phosphor layer with red, green, and blue zones Close-up of the phosphor-coated inner side of the sc
10、reen,Cutaway rendering of a color CRT,CATHODE-RAY TUBE (CRT) - is one of the main elements of an oscilloscope.,One of anodes, which accelerate the electrons, is placed close to the screen. The high positive voltage is applied to this electrode. Under the action of the applied voltage the electrons a
11、re moved with acceleration from cathode to anode. In the absence of the voltage applied to deviating plates of the capacitor the electron beam will be incident on the screen in the center brightening a point in the fluorescing layer. In oscilloscope the analyzed signal after amplification is applied
12、 to vertical deviating plates, while the periodic sawtooth signal is applied to horizontal plates.,http:/physics- a result the electron beam “draws“ the dependence of the investigated signal on time on the screen of the tube. Reaching the right side of the screen the beam has to be returned to an in
13、itial point at the left side. Thus, if CRT is not blanked during this retrace, then the beam will leave a track crossing the image of investigated signal. For this reason, during retrace a negative voltage is applied to control electrode situated near to cathode and electrons are locked by such a wa
14、y at the electron gun. As a result, the electron beam will be discontinuous, as shown in animation.,Related Web Sites for CRT Animation,http:/highered.mcgraw- http:/physics- The Cathode Ray Tube site: http:/members.chello.nl/h.dijkstra19/page3.html How Television Works: http:/ 電子在直流電場中之偏折：利用水平電板X(4)
15、及垂直電板Y(5)所提供的電壓，產生均勻電場(E)，使電子束偏折，如電板Y長L, 兩板距離d, 直流電位差V2 (E = V2/d)，電子離開電板後距螢光幕D，則電子在Y方向偏折SE，使螢光幕(XY面)在Y軸 SE 處產生一亮點。,X, Y等速直線運動,X：等速直線運動 Y：等加度運動,3. 電子在交流電場中之偏折：若在電板Y加交流電頻率 f = /2 = 1/T因高頻，電子在螢光幕成一長為l的亮線Note：一般家電 Vrms = 110 V, f = 60 Hz,4. 電子在磁場中之偏折利用共軸雙線圈螺線管之均勻磁場(B)來偏折電子束如磁場在x方向 (長L)，電子離開磁場後距螢光幕 D則電子
16、在Y方向偏折 SB ( Sm)螢光幕(XY面)Y軸上SB有一亮點 5. 同時在電場及磁場的作用下並使電子不偏折SE + SB = 0eE = evzBvz = E/B 代入 SE 或 SB 即可求電子的荷值 (e/m) 比,實驗步驟：I. 陰極射線管電源 1. 陰極射線管(X = 60 mm, Y =54 mm,D = 115 mm, L = 11 mm, d = 1.65 mm)插入CRT基座(Unilab 031.502)X為X電板輸入端Y為Y電板輸入端A1為最後加速陽極Z接柵極 2. CRT基座接CTR電源供應(032.332)之五腳CRT插座(tube supply)注意：高壓電源!接電路前, 確定電源供應器開關為關(off)(燈暗) 3. 調整CRT亮點之亮度(brill)(加速陽極)及焦距(focus)(聚焦陽極),
