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9.1 THERMIONIC EMISSIONS 2020 Flipbook PDF
9.1 THERMIONIC EMISSIONS 2020
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9.1 THERMIONIC EMISSIONS | DATE : …………………..
IDEA
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THERMIONIC EMISSIONS
Label with: cathode, anode, EHT, +/-, cathode ray, 6V
What is thermionic emission?
What is cathode ray?
Surface of metal consists of a large number of ………………… which are free to move but remain inside the metal. At room temperature, the electrons are free to move but the electrons cannot escape at the surface because they are held back by the ………………………… forces of the atomic nucleus. If the metal is heated at a high temperature, some of the free electrons may gain sufficient thermal energy to ……………………. from the metal. The process of emission of electrons from the surface of heated metal is known as ……………………………….. ……………………… Electrons are easily emitted if the metal is coated with an oxide of barium or strontium
Cathode ray is ……………………………………………………………………………… ……………………………………………………………………………… The properties of cathode ray can be studied using i) Maltese cross ii) Deflection tube
Bubble map of PROPERTIES OF CATHODE RAY
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MALTESE CROSS – TO STUDY THE PROPERTIES OF CATHODE RAYS
Procedure
Observation on the fluorescent screen
Discussion
1. Connect only the 6.3 V power supply to the filament
2. Connect the 6.3 V and EHT to the cathode and anode
3. Investigate the properties of cathode rays in a magnetic field Bring a pole of a bar magnet near to the neck of the tube
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DEFLECTION TUBE – TO STUDY THE PROPERTIES OF CATHODE RAYS
EHT to the metal plates is switched off
EHT to the metal plates is switched on
EHT to the metal plates is switched on and reversed
EHT to the metal plates is switched on and increased
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ENERGY TRANSFORMATION IN THE CATHODE RAY TUBE:
(i)
What physics principle involved in the CRO?
(ii)
State the energy transformation in the CRO.
(iii)
Derive the formula to determine speed of an electron.
EXERCISE 9.1: 1. One of the electron guns in a color television emits an electron beam which is accelerated by a potential difference of 240 V before hitting the deflection plate. (a) What is initial electric potential energy of an electron (b) The maximum kinetic energy of an electron (c) The maximum velocity of an electron. [ e = 1.6 x 10
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-19
C; m= 9 x 10
-31
kg]
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2.
Diagram 3.1 shows a cross section of a Maltese cross tube used to study the characteristics of cathode ray. Rajah 3.1 menunjukkan keratan rentas sebuah tiub palang Maltese yang digunakan untuk mengkaji sifat-sifat sinar katod.
Diagram 3.1 (a) What is the meaning of cathode ray? Apakah yang di maksudkan dengan sinar katod?
[1 mark] (b) (i)
When switch S1 and switch S2 are turned on, two overlapping shadows are formed on the screen. Explain why the shadows are formed on the screen. Apabila suis S1 dan suis S2 dihidupkan, dua bayang-bayang yang bertindih terbentuk diatas skrin. Terangkan kenapa bayang-bayang ini terbentuk di atas [1 mark]
(ii) Why is there a vacuum in the Maltese cross tube? Mengapa tiub palang Maltese berada dalam keadaan vakum?
[1 mark] (c)
(i)
Calculate the speed of cathode ray in the Maltese cross tube. Hitungkan halaju sinar katod di dalam tiub palang maltese . -19 -31 [Charge of electron, e = 1.6 x 10 C; Mass of one electron, me = 9 x 10 kg]
[2 marks]
(ii) How can the speed of cathode ray be increased? Bagaimana laju sinar katod boleh ditingkatkan?
[1 mark]
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(d) Diagram 3.2 shows a pair of magnet with opposite poles is placed at the sides of the tube. One of the shadows deflects. Rajah 3.2 menunjukkan sepasang magnet dengan kutub berbeza diletakkan pada sisi tiub tersebut. Satu daripada bayangbayang tersebut terpesong.s
Diagram 3.2 Rajah 3.2 (i) By using an arrow, show the direction of the shadow which deflects in Diagram 3.2. Dengan menggunakan anak panah, tunjukkan arah pesongan bayang pada skrin di Rajah 3.2. [1 mark] (ii) State the physics rule used to determine the direction of the shadow. Nyatakan peraturan fizik yang digunakan untuk menentukan arah bayang tersebut.
[1 mark]
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CATHODE RAY OSCILLOSCOPE A CRO is an instrument that converts electronic and electrical signals to a visual display – PARTS & COMPONENTS
Write the function of each part/component: Electron gun
to produce a ……………………….. beam of electrons
Filament
to ………………… up the cathode
Cathode
emits electrons through the process of ……………………….. emissions
Control grid
…………………………. the number of electrons in the electron beams
Focusing anode
To …………………… the electrons into a beam and to ………………………….. electrons from the area of the control grid.
Accelerating anode
To …………………………. the electron beam towards the screen
y-plate
To deflect cathode ray in ……………………..
x-plate
To deflect cathode ray in ……………………..
Pendafluor screen
To convert …………………….. energy to …………………….. energy
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CATHODE RAY OSCILLOSCOPE –KNOBS AND APPLICATIONS
Brightness Focus
Y-shift
X-shift Figure 9.3
Y-Gains
Time-base Y-input
What is Cathode Ray Oscilloscope?
Application of CRO
Earth
X-input
A cathode ray tube converts electronic and electrical signals to a visual display The graph produced consists of a horizontal axis, which is normally a function of time , and a vertical axis, which is a function of the input y The components in a cathode ray tube consist of a vacuum glass tube with an electron gun, a deflection system for deflecting the electron beam and a fluorescent-coated screen.
1.
A voltmeter to measure potential difference
2.
A timer to measure short time intervals
3.
A tool to display wave forms
DISPLAY WAVE FORMS USING A CRO (a) No input Time-base: OFF
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Time-base: ON
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(b) Y-Gain: 1V/div; Input: V = 4V dc
Time-base: OFF
Time-base: ON
(c) Y-Gain: 5V/div; Input : V = 10 V dc (connected in opposite terminals) Time-base: OFF
Time-base: ON
(d) Y-Gain: 2V/div; Time base : 10 ms/div Input : Vp = 6V ac; Period = 40 ms Time-base: OFF
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Time-base: ON
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MEASURE SHORT TIME INTERVALS
Time taken, t between two beats =
MEASURING POTENTIAL DIFFERENCE USING THE CRO time-base off time-base on
(a)
1.
What is the value of the dc voltage in figure (a) and (b) if the Y-gain control is 1 V/div?
(b)
(c)
(d)
Y-gain = 2 V/div Time-base = 5 ms/div 2.
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Find (a) peak voltage, Vp (b) peak to peak voltage, Vpp (c) root mean square voltage, Vrms (d)period, T (e)frequency, f
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3. If the controls on the CRO are set to 0.5 V/div and 2 ms/div, find (a) the peak voltage, V p and root mean square voltage, Vrms
(b) the frequency of the input signal
(c) (i) Sketch the trace displayed on the screen if the settings are changed to 1 V/div. Time-base remains. (ii) Sketch the trace displayed on the screen if the settings are changed to 1 V/div and 4 ms/div
(i)
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(ii)
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EXERCISE 9.4
4.
A student uses CRO to study the output voltage from a bicycle dynamo. The figure shows the trace and setting of the CRO for one particular speed.
(a) What are the setting of the time-base and the Y-gain control respectively?
(d) What is the root mean square voltage, Vrms?
(b) What is the peak voltage, Vp? (e) What is the period of the trace?
(c) What is the peak-to-peak voltage, Vpp?
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(f) Calculate the frequency of rotation of the dynamo.
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9.1 USES OF CRO 1. SPM 2005/45 Which the diagram shows the correct movement of an electron beam in an electric field? Rajah manakah menunjukkan pergerakan alur electron yang betul apabila berada di dalam medan elektrik?
3. SPM 2009/44 Diagram 26 shows an audio signal generator connected to a cathode to a cathode ray oscilloscope, CRO.
Which signal shows the loudest and the highest pitched audio signal?
2. SPM 2008/44 Diagram 27 shows a cathode being heated by a filament. Rajah 27 menunjukkan katod sedang dipanaskan oleh filamen.
4. SPM 2011/21 Diagram 15 shows the process of electrons escaping from the surface of a heated metal.
Which particle is emitted from the cathode? Zarah manakah dikeluarkan dari katod? A. B. C. D.
Proton Neutron Electron Alpha
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Diagram 15
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9.1 THERMIONIC EMISSIONS | DATE : ………………….. What is this process? A B C D
Radiation Evaporation Rectification Thermionic emission
7. SPM 2011/47 Diagram 33 shows the structure of a cathode ray oscilloscope.
5. SPM 2011/42 Diagram 29 shows a shadow formed on the screen of a Maltese Cross Tube. The shadow is deflected by the magnets. Which component, A, B, C or D causes the electrons to accelerate?
The direction of the deflection is determined by using A the Fleming’s left hand rule B the Fleming’s right hand rule C the right hand grip rule 6. SPM 2011/46 The doping process of pure semiconductor with pentavalent element will A cause the semiconductor to be negatively charged B produce p-type semiconductor C cause the resistance of the semiconductor to increase D produce majority charged carrier which are electrons
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8. SPM 2010/4 Diagram 4.1 shows a bright spot, P, formed on the screen of a cathode-ray oscilloscope, CRO, when it is switched on. Rajah 4.1 menunjukkan suatu bintik cerah, P, terbentuk di atas skrin osiloskop sinar katod, OSK, apabila suis dihidupkan.
(a) What is the meaning of cathode ray? Apakah yang dimaksudkan dengan sinar katod?
[1 mark] (b) Explain how the bright spot is formed on the screen of the CRO. Terangkan bagaimana bintik cerah terbentuk di atas skrin OSK.
[2 marks]
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9.1 THERMIONIC EMISSIONS | DATE : ………………….. (c) Diagram 4.2 shows the bright spot is displaced to Q when a direct current, d.c., supply, is connected to the Y-input of the CRO. Rajah 4.2 menunjukkan bintik cerah tersesar ke Q apabila bekalan arus terus, at disambungkan kepada input-Y OSK.
The Y-gain of the CRO is set at 2V/division Calculate the input voltage of the d.c. supply. Gandaan-Y bagi OSK disetkan kepada 2V/bahagian. Hitung voltan input bekalan at. [2 marks] (d) Diagram 4.3 shows an alternating current, a.c. supply, is connected to the CRO. Rajah 4.3 menunjukkan bekalan arus ulang alik, au disambungkan kepada OSK.
Draw the output signal on the screen in Diagram 4.3 when the peak voltage of the a.c. supply is 6V and the time-base is switched off. Lukiskan isyarat output pada skrin dalam Rajah 4.3 apabila voltan puncak bekalan au ialah 6V dan dasar-masa ditutup. [2 marks]
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9. SPM 2016
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