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# SPM PHYSICS FORM 5 electronics

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### SPM PHYSICS FORM 5 electronics

1. 1. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics CHAPTER 9: ELECTRONICS9. 1: USES OF THE CATHODE RAY OSCILLOSCOPE (C.R.O)9.1.1: Thermionic Emission1. What is Thermionic Emission?………………………………………………………………………………………………2. (a) Label the figure of a vacuum tube: Figure 9.1 (b) The figure shows ………… emitted are accelerated ………….. the anode by the high …………………… between the cathode and anode. (c) A beam of electrons moving at high speed in a vacuum is known as a ………………..3. Factors that influence the rate of thermionic emission Factor Effect on the rate of thermionic emission Temperature of the cathode When the temperature of the cathode increases, the rate of thermionic emission increases. Surface area of the cathode A larger surface area of the cathode increases the rate of thermionic emission. Potential difference The rate of thermionic emission is unchanged, when the between the anode and potential difference increases, but the emitted electrons cathode. accelerate faster towards the anode.9.1.2 Properties of Cathode Rays1. List the four characteristics of the cathode rays.(i) ……………………………………………………………………..(ii) …………………………………………………………………….(iii) ……………………………………………………………………(iv) …………………………………………………………………… 1
2. 2. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: ElectronicsEnergy Change in A Cathode Ray Figure 9.2 By using the principle of conservation of energy, 1 2 v = velocity of electron mv = eV , V = Potential difference between Anode and 2 Cathode 2eV e = Charge on 1 electron = 1.6 x 10 -19 C Maximum velocity of electron, v = m m = mass of 1 electron = 9 x 10 -31 kg 1. In a cathode ray tube, an electron with kinetic energy of 1.32 × 10-14 J is accelerated. Calculate the potential difference, V between the cathode and the accelerating anode. [ e = 1.6 x 10 -19 C] Solution: 1 Kinetic energy = mv 2 = eV 2 1.32 × 10 = 1.6 × 10 −19 V -14 V = 8.25 × 10 3 V 2. In a vacuum tube, a cathode ray is produced and accelerated through a potential difference of 2.5kV. Calculate… (a) The initial electric potential energy of the cathode ray. (b) The maximum velocity of the electron. [ e = 1.6 x 10 -19 C; m= 9 x 10 -31 kg] Solution: (a) Electric potential energy = eV = 1.6 × 10 −19 × 2.5 × 10 3 = 4 × 10 −16 J 1 4 × 10 −14 (b) mv 2 = eV = 4 × 10 −14 v = 2 ×2 v = 8.89 × 1016 = 2.98 × 10 8 ms -1 2 9 × 10 −31 3. If the potential difference between the cathode and the anode in a CRO is 3.5 kV, calculate the maximum speed of the electron which hit the screen of CRO. [ e = 1.6 x 10 -19 C; m= 9 x 10 -31 kg] Solution: 1 2 mv = eV = 1.6 × 10 −19 × 3.5 × 10 3 = 5.6 × 10 −16 2 5.6 × 10 −16 v2 = × 2 = 1.24 × 1015 v = 1.24 × 1015 = 3.53 × 10 6 ms -1 9 × 10 −31 2
3. 3. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics9.1.3 Structure of the Cathode Ray Oscilloscope 1. Label all parts of Cathode Ray Oscilloscope below. Figure 9.3 2. Fill in the blank all components and its functions. Main part Component Function Electron gun Deflecting system Fluorescen t screen 3
4. 4. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics9.1.4 : The working Principle of the Cathode-Ray Oscilloscope.1. Fill in the blank the structure of CRO. Figure 9.49.1.5 Uses of the CRO. 1. The uses of cathode-ray oscilloscope are: (a) ……………………………………….. (b) ………………………………………. (c) ………………………………………. To measure a D.C voltage: The unknown voltage, V = (Y-gain) × h To measure a A.C voltage: Peak-to-peak voltage, Vpp = (Y-gains) × h 1 Peak voltage, Vp = (Y-gains) × (h) 2 1 Effective voltage or root-mean-square voltage, Vr.m.s = Vp 2 Short time intervals, t = no. of divisions between two pulses × time-base value. 2. If the CRO in figure uses Y-gains of 1.5 Vcm-1, calculate the value of Vpp. Solution: V = 1 .5 × 2 .0 = 3 .0 V Figure 9.5 4
5. 5. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 3. The figure shows a trace on a CRO set at 5 Volt per division on the vertical axis. (a) What is the maximum voltage (peak voltage) indicated? Solution: 1 Peak voltage, Vp = (Y-gains) × (h) 2 1 V P = 5 V/div × × 4 divs 2 Figure 9.6 V P = 10 V 4. Figure shows a trace on an oscilloscope for an a.c source. If the Y-gain is set to 1.5 Vcm-1 and the time-base is 2 ms cm-1. (a) Calculate the peak voltage,Vp of the a.c source. Solution: 1 V P = 1.5 Vcm -1 × × 4 cm 2 Figure 9.7 V P = 3 .0 V (b) Calculate the frequency, f of the a.c source. Solution: T = 4cm × 2 ms cm-1 1 T = 8 ms ∴f = = 125 Hz T (c) Sketch the trace displayed on the screen if the settings are changed to 1 Vcm-1 and 1 ms cm-1. 5. The diagram shows the trace on the screen of a CRO when an a.c voltage is connected to the Y-input. The Y-gain control is set at 2 V/div and the time base is off. Calculate the value of : (a) Peak-to-peak voltage, Vpp (b)Peak voltage, Vp. (c)Root-mean-square voltage, Vr.m.s Figure 9.8 5
6. 6. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics Solution: (a) Peak-to-peak voltage, Vpp = (Y-gains) × h = 2V/div × 6 divs = 12 V (b) Peak voltage, Vp = 6 V 1 1 (c) Vr.m.s = Vp = × 6 = 4.24 V 2 2 5 divs 6. When two claps are made close to a microphone which is connected to the Y-input and earth terminals, both pulses will be displayed on the screen at a short interval apart as Figure 9.9 shown in figure below. Measure the time lapse between the two claps. Solution: Length between two pulses = 5 divs Time taken, t = 5 divs × 10 ms/div = 50 ms ∴Time interval = 0.05 s 7. Figure shows the trace displayed on the screen of a CRO with the time-base is set to 10 ms/div. What is the frequency, f of the wave? Solution: Distance for two complete wave = 2 divs ∴ Time taken = 2 divs ×10ms/div = 20 ms 1 1 ∴frequency, f = = = 50 Hz T 20 ms Figure 9.10 8. An ultrasound signal is transmitted vertically down to the sea bed. Transmitted and reflected signals are input into an oscilloscope with a time base setting of 150 ms cm-1. The diagram shows the trace of the two signals on the screen of the oscilloscope. The speed of sound in water is 1200 ms-1. What is the depth of the sea? Solution: Time taken for ultrasonic waves to travel through a distance of 2 d = time between P and Q = 5 cm × 50 ms sm -1 = 250 ms = 0.25 s 2d Speed of ultrasonic waves, V = t 1200 × 0.25 Hance, d = = 150 m Figure 9.11 2 6
7. 7. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics9.2 SEMICONDUCTOR DIODES9.2.1 Properties of Semiconductors 1. Semiconductor is a group of materials that can conduct better than insulators but not as …………………………………………………………………………….. good as metal conductors. ……………………………. 2. Give the examples of pure semiconductor: Silicon (a) …………………………… Germanium (b) …………………………... Selenium (c) …………………………… 9. What is the “doping” process? Doping is a process of adding a certain amount of other substances called dopants ……………………………………………………………………………………………… such as Antimony and Boron to a semiconductor, to increase its conductivity. ……………………………………………………………………………………………… 10. Base on the figure, complete the statement below. (a) n-type semiconductors Figure 9.12 pentavalent Silicon like Silicon doped with ………………atoms such as …………… or antimony increases phosphorus …………. the number of free electron. The phosphorus atoms have five four …….. valence electrons, with …… being used in the formation of covalent bonds. The fifth electron is free to move through the silicon. The silicon has negative electrons ….………………….. as majority charge-carriers and it thus known as an n-type semiconductor. 7
8. 8. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (b) p-type semiconductors Figure 9.13 trivalent Semiconductor like Silicon doped with ……………….. atoms such as ………… Boron three or indium has more positive holes. The Boron atoms have only …………. one valence electrons; hence ………. of the covalent bonds has a missing electron. This missing electron is called a ‘positive hole’. The majority charge-carriers in positive holes this semiconductor are the ………………. and this semiconductor is thus known as a p-type semiconductor.9.2.2 The p-n junction (Semiconductor diode) 1. What is the function of semiconductor diode? The function of semiconductor diode is to allow current to flow through it in one direction ……………………………………………………………………………………………… only. ……………………………………………………………………………………………… 2. Label the p-n junction below and draw a symbol of the diode. p-type n-type Positive hole Negative electron Symbol p-n junction Figure 9.13 8
9. 9. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 3. (a) Forward-biased (i) positive terminal In forward-bias, the p-type of the diode is connected to …………………. and the n- negative terminal type is connected to the …………………… of the battery. (ii) Complete the diagram below to show the diode is in forward-bias. + - The bulb is light up The bulb does not light up Figure 9.14 (iii) Draw arrows to show the current, electrons and holes flow in the diagram.(b) Reverse-biased (i) In reverse-bias, the p-type of the diode is connected to …………………. , and the n- negative terminal positive terminal type is connected to the …………………… of the battery. (ii) Complete the diagram below to show the diode is in reverse-bias. - + The bulb is light up The bulb does not light up Figure 9.15 4. Draw arrows to show the current, electrons and holes flow in the diagram. 5. What the meaning of rectification? Rectification is a process to convert an alternating current into a direct current by using a diode. ……………………………………………………………………………………………… ……………………………………………………………………………………………… 9
10. 10. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 6. The figure shows a half-wave rectifier circuit that is connected to CRO. (i) Sketch waveform of the voltages observed on the CRO screen when the time- base is on. Figure 9.16 (ii) Sketch waveform of the voltages observed on the CRO screen when a capacitor is connected in parallel across a resistor, R. Figure 9.17 7. The figure shows a full-wave rectifier circuit that is connected to CRO. (i) Draw arrows to show the current flow in the first half cycle and to show the current flow in second half cycle in the diagram. (ii) Sketch the waveform of the voltages observed on the CRO screen when the time-base is on. a To CRO Figure 9.18 10
11. 11. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (iii) Sketch waveform of the voltages observed on the CRO screen when a capacitor is connected in parallel across a resistor, R. a To CRO Figure 9.19 8. What is the function of the capacitor? Acts as a current regulator or smoother. ……………………………………………………………………………………………....9.3 TRANSISTOR9. 3.1 Terminals of a Transistor. 1. What is a transistor? A transistor is a silicon chip which has three terminals labeled as base, collector and emitter. ……………………………………………………………………………………………… 2. Draw and label symbol of n-p-n transistor and p-n-p transistor. Collector, C Collector, C Base, B Base, B Emitter, E Emitter, E n-p-n transistor p-n-p transistor 3. State the function for each terminal in a transistor. (a) The emitter, E : Acts as a source of charge carriers, providing electrons to the collector. ………………………………………………………………………………. (b) The base, B : Controls the movement of charge carriers (electrons) from the emitter (E) to the collector (C). ………………… …………………………………………………………… (c) The collector, C: Receives the charge carriers from the emitter (E) ………………………………………………………………………………... 11
12. 12. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics9.3.2 Transistor circuit 1. (a) Transistor circuit with 2 batteries. BE Base circuit : …………………………………. CE Collector circuit : …………………………………. Ib Base current : …………………………………. Ic Collector current : …………………………………. R1 Limit the base current : …………………………………... Ie Limit the collector current R2 : …………………………………... Figure 9.20 Supply energy to the base circuit E1 : …………………………………... Supply energy to circuit.(b) Transistor circuit with 1 battery. E2 : …………………………………... Potential divider Rx : …………………………………... Potential divider Ry : …………………………………... Remember: Ie = Ib + Ic Ie > Ic > Ib Ie ∆Ic >>>>∆Ib No Ib, No Ic Figure 9.21 2. The working circuit of a transistor used as a potential divider can be connected as shown in figure. The voltage across Rx and Ry can be calculated as follows. ⎛ Rx ⎞ ⎛ Ry ⎞ Vx = ⎜ ⎟V VY = ⎜ ⎟V ⎜R +R ⎟ ⎜R +R ⎟ ⎝ x y ⎠ ⎝ x y ⎠ 12
13. 13. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (a) Figure shows a transistor circuit. The bulb can be lighted up when potential difference, V across resistor P is 2V and resistance P is 10 kΩ. Calculate the maximum resistance, S so that the bulb is lighted up. Solution: ⎛ Rp ⎞ Vp = ⎜ ⎟V Bulb ⎜R +R ⎟ ⎝ s p ⎠ ⎛ 10 × 10 3 ⎞ 2V =⎜ ⎟ ⎜ R + (10 × 10 ) 6 V 3 ⎟ ⎝ s ⎠ RS + 10 × 10 = 30000 3 RS = 20000 Ω = 20 kΩ Figure 9.229.2.3 Transistor as an Automatic Switch. 1. Complete the statement below. RX IC Battery voltage IB Base voltage RY IE Figure 9.23 The switching action is produced by using a potential divider. In a working circuit variable resistor shown in figure, a resistor, RX and a …………………………. are being used to form a zero potential divider. If the variable resistor is set to zero, the base voltage is ………. and off the transistor switches ………. However, if the resistance of the variable resistor is increases increased, the base voltage will……………. When the base voltage reached a certain minimum value, the base current, IB switches on the transistor. A large collector current, IC flows to light up the bulb. 2. What type of transistor is used in an automatic switch circuit? Transistor n-p-n ……………………………………………………………………………………………… 13
14. 14. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 3. (a) Light Controlled Switch (i) Complete the statement below. 10 kΩ R IC 1kΩ 6V IE LDR Figure 9.24 Figure shows a transistor-based circuit that functions as a light controlled switch. light-dependent resistor The ……………………….. (LDR) has a very high resistance in the …….… and a low dark bright light resistor resistor in ………………... R is a fixed ……………. The LDR and R form a potential divider in the circuit. low In bright light, the LDR has a very ………. resistance compared to R. Therefore, the base low voltage of the transistor is too …….. to switch on the transistor. large In darkness, the resistance of the LDR is very ……… and the voltage across the LDR is high ……… enough to switch on the transistor and thus lights up the bulb. This circuit can be on used to automatically switch …… the bulb at night. (ii) Complete the table below. Condition RLDR VLDR R VR Transistor (ON or OFF) Daylight low low high high OFF Darkness high high low low ON Remember ∆Ic >>>>∆Ib (iii) How can the circuit in figure be modified to switch on the light at daytime? The circuit can be modified by interchanging the positions of the LDR and resistor R. ………………………………………………………………………………………….. 14
15. 15. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (b) A Heat-Controlled Switch (i) Complete the statement below. Thermistor Diode Relay RB Alarm R Figure 9.25 Figure shows a transistor-based circuit that function as a heat controlled switch. thermistor high A ……………..is a special type of resistor. Its resistance becomes very ……… when it is drops cold. When the thermistor is heated, its resistance ………… rapidly. At room high temperature, the thermistor has a ………. resistance compared to R. Therefore, the base voltage of the transistor is too low to switch on the transistor. resistance When the thermistor is heated, its ……………. drops considerablely compared to R. on Therefore, the base voltage VB is high enough to switch ……. the transistor. When the ……………., on transistor is switch on, the relay switch is activated and the relay is switched ………. The circuit can also be used in a fire alarm system. (ii) What is the function of a diode is used in the heat-controlled circuit? To protect the transistor from being damaged by the large induced e.m.f in the relay ………………………………………………………………………………………….. coil when the collector current, IC drops to zero. ………………………………………………………………………………………….. (iii) Complete the table below. Temperature RThermistor VThermistor R VR Transistor (ON or OFF) High low low high high ON Low high high low low OFF Remember ∆Ic >>>>∆Ib 15
16. 16. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics9.2.4 Transistor as a Current Amplfier 1. Complete the statement below. mA R2 IC R1 µA R IB IE Figure 9.26 A transistor functions as a current amplifier by allowing a small current to control a collector current larger current. The magnitude of the …………………., IC is primarily determined by the base current small big ………………….., IB. A ……….. change in the base current, IB will cause a …….. change in the collector current, IC. The current amplification can be calculated as follows: ∆I C Current Amplification = ∆I B 2. Name the type of the transistor used. n-p-n transistor ……………………………………………………………………………………………… 3. What will happened to the readings of the miliammeter, mA and microammeter, µA when the resistance of R is reduced? The readings on miliammeter and microammeter increase. ……………………………………………………………………………………………… 4. A transistor is said to have two states, the ‘ON’ state and ‘OFF’ state. (a) Explain the meaning of the ‘ON’ state of a transistor. When a transistor is in the ‘ON’ state, currents flow in the base and in the collector circuit. ……………………………………………………………………………………… (b) Explain the meaning of the ‘OFF’ state of a transistor. When a transistor is in the ‘ON’ state, there is no current in the base and in the collector ……………………………………………………………………………………… circuit. ……………………………………………………………………………………… (c) What is the function of the rheostat, R? To change the base current. ……………………………………………………………………………………… (d) What is the function of the resistor, S? To control and limit the base current. ……………………………………………………………………………………… 16
17. 17. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics9.4 Logic Gates9.4.1 Analysing Logic gates 1. What is a logic gate? A switching circuit that is applied in computer in computer and other electronic devices. ……………………………………………………………………………………………… 2. Complete the table below. Gates Symbol Truth table Input Output A B Y A 0 0 0AND gate Y 0 1 0 B 1 0 0 1 1 1 Input Output A B Y A 0 0 0 OR gate Y 0 1 1 B 1 0 1 1 1 1 Input Output A Y A 0 1 Y NOT gate 1 0 17
18. 18. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics Input Output A B Y NAND A 0 0 1 gate Y 0 1 1 B 1 0 1 1 1 0 Input Output A B Y A 0 0 1 NOR gate Y 0 1 0 B 1 0 0 1 1 09.4.2 Combinations of logic Gates 1. Find the output Y for each combination of logic gates. 0011 A P 1100 Y 0100 B 0101 Figure 9.27 The truth table: Input Output A B P Y 0 0 1 0 0 1 1 1 1 0 0 0 1 1 0 0 18
19. 19. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 2. 0011 P A 1100 Y 1000 B Q 1010 0101 Figure 9.28 The truth table: Input Output A B P Q Y 0 0 1 1 1 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 3. 0011 A X 0001 B 0101 Y 0100 B 1010 The truth table: Figure 9.29 Input Output A B B X Y 0 0 1 0 0 0 1 0 0 1 1 0 1 0 0 1 1 0 1 0 19
20. 20. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 4. 0011 A P 1110 Y 0110 0111 B Q 0101 Figure 9.30 The truth table: Input Output A B P Q Y 0 0 1 0 0 0 1 1 1 1 1 0 1 1 1 1 1 0 1 0 5. A P B Y B The truth table: Figure 9.31 Input Output A B P Q Y 0 0 1 0 0 0 1 1 1 1 1 0 1 1 1 1 1 0 1 0 20
21. 21. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics 6. Figure shows a logic gate system which switches on an air-conditioner automatically. Input J Light detector L Air-conditioner Heat detector Input K Figure 9.32 Keys: The light detector (Input J): In the day, logic “1”. At night, logic “0”. The heat detector (Input K): Hot, logic “1”. Cool logic “0”. (a) Complete the truth table below: Input Output J K L 0 0 0 0 1 1 1 0 0 1 1 1 (b) Based on the truth table in (a), state the conditions in which the air-conditioner conditions in which the air-conditioner will operate and function normally. - On a hot say or daytime – On a hot night ……………………………………………………………………………………………… 21
22. 22. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: ElectronicsReinforcement Chapter 9Part A: Objective questions A. 2.5 V B. 5.5 V1. Which of the following is not a property C. 7.5 V of cathode rays? D. 12.5 V A. It is positively charged. E. 15.0 V B. It travels in a straight line. C. It can be deflected by magnetic field. 5. In p-type semiconductor D. It can be deflected by electric field. A. The number of holes are equal to the number of electrons.2. Cathode rays consists of B. The number of the holes are more A. Fluorescent particles than the number of electrons. B. Light rays from a screen C. The number of the holes are less than C. Beams of fast moving particles the number of electrons. D. Light rays from hot filament 6. Which of the following is not true about3. A beam of electrons is being deflected diode? due to a potential difference between A. It can be used to rectify alternating plates P and Q. current. P B. It can only conduct electricity when Figure 9.33 it is connected in forward in forward bias in a circuit. Q C. It is formed by joining an n-type and a p-type semiconductor. Which of the following statements is not D. The majority charge carriers in the true? diode are electrons. A. The potential at plate P is positive. B. The deflection would be greater if 7. The figure 9. 35 shows the arrangement the potential difference is greater. of silicon atoms after an atom P is doped C. The deflection would be greater if to form an extrinsic semiconductor. the electrons are moving faster. D. The electron beam will return to straight line if a suitable magnetic Figure 9.35 field is applied between the plates.4. The figure 9.34 shows the trace displayed on a CRO with the Y-gain control is turned to 3.75 V/div. Which of the following is not true? What is the maximum value of the A. The conductivity of the potential difference being measured? semiconductor increases. B. The semiconductor becomes an n- type. C. The majority charge carrier is Figure 9.34 electron. D. Atom P is a trivalent atom. 22
23. 23. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics8. The figure 9.36 shows a rectifier circuit. components connected in a circuit. Which of the following statements is Which of the following bulbs will light true? up continuously when the switch is on? A. P and Q only P B. P, Q and R only C. R and S only Q D. P, Q and S only 11. Which of the following circuits shows Figure 9.36 the connect directions of the base current A. A rectifier changes d.c to a.c. IB, emitter current, IE and collector B. Device P allows current to flow in current, IC? any directions. C. Device Q acts as a rectifier. D. The rectifier circuit would still work if device P is reversed.9. The figure 9.37 shows a circuit consisting of two diodes and a bulb. When the switch is on, the bulb does not light up. What needs to be done to light up the bulb? Figure 9.37 A. Replace the diode with a new one. B. Reverse the connection of the diode. C. Increase the number of bulbs. D. Connect a resistor in series with the bulb.10. Figure 9.38 Figure 9.38 shows four identical bulbs, P, Q, R and S, and four electronic 23
24. 24. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics12. Which of the following statements about a transistor is not true? A. A transistor can act as an amplifier B. A transistor can act as a relay switch. C. The function of a transistor is the same as that of two diodes. D. A transistor is a combination of two types of semiconductors. Figure 9.41 A. 3 kΩ B. 4 kΩ Figure 9.39 C. 5 kΩ D. 6 kΩ E. 7 kΩ13. What is the function of the transistor 16. The figure 9. 42 shows a transistor circuit shown in figure 9.39? circuit being used to amplify sound. A. As an amplifier B. As a rectifier M- Microphone C. As a switch device C- Capacitor D. As a modulator S- Speaker14. The figure 9.40 shows a transistor being used as a current amplifier. IC IB Figure 9.42 Which of the following is not correct about the circuit? A. T is an npn transistor Figure 9.40 B. The capasitor prevents d.c current but allows a.c current to pass through Which of the following is correct? it. A. IB > IC C. Speaker amplifies the sound. B. IB = IC D. R1 and R2 act as potential divider. C. IB < IC 17. The figure 9.43 shows a logic gate15. Figure 9.41 shows a circuit consisting of circuit with input signals, X and Y. a transistor which acts as an automatic switch. When the potential difference across the thermistor is 3 V and the resistance of the thermistor is 1000 Ω, Figure 9.43 the resistance value of resistor, R is .. Which of the following is the output signal? 24
25. 25. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics What is gate X? A. AND B. NOR C. OR D. NAND18. The figure 9.44 shows a logic gate circuit. 20. The figure 9. 45 shows a combination of three logic gates in a logic circuit. When inputs P and Q are both 1 output Y is 1. Figure 9.43 J Which of the following is the output Y signal Z? K A. 0110 B. 1010 C. 1110 Figure 9.45 D. 0101 Which of the following logic gates can19. The figure 9.44 shows the combination be used to represent J and K? of three logic gates. J K A. AND NOR B. NAND NOR Figure 9.44 C. OR AND D. NOR AND The truth table for the combination of tree logic gates is as follows.Part B: Structured Questions.1. Figure 9.46 shows a trace obtained on an oscilloscope screen when an a.c voltage is connected to the Y-plates of an oscilloscope. Scale: 1 division = 1 cm Figure 9.46 The Y-gain is set at 3 V/cm The time base is set at 5 ms/cm (a) Explain what is meant by thermionic emission. Emission of electrons from the surface of a metal by heat. ……………………………………………………………………………………………… (b) Determine the peak voltage of a.c voltage. 2 x 3 = 6V ……………………………………………………………………………………………… (c) Determine the time for one complete oscillation on the screen. 2 x 5 = 10 ms ……………………………………………………………………………………………… 25
26. 26. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (d) What is the frequency of the a.c voltage? f =1/T=50 Hz ……………………………………………………………………………………………… (e) With the same a.c voltage applied to the oscilloscope, the time-base setting is altered to 2.5 ms/cm and the Y-gain setting is altered to 2 V/cm. On the space below, sketch the new trace would appear on the oscilloscope.2. Figure 9. 47 shows a full wave bridge rectifier. The a.c supply has a frequency of 50 Hz. Figure 9.47 (a) When the polarity of the a.c supply voltage is positive at A, state the two diodes which are forward biased. D1 and D3 ………………………………………………………………………………………….. (b) When the polarity of the a.c supply voltage is negative at A, state the two diodes which are forward biased. D2 and D4 …………………………………………………………………………………………… (c) Using the axes in figure 9.48, sketch the voltage-time graph across the resistor, R. Voltage/V Time/ms Figure 9.48 26
27. 27. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (d) On the figure 9.49, sketch the voltage-time graph across the resistor if a capacitor is connected across the resistor if a capacitor is connected across the resistor R parallel with the resistor. Voltage/V Figure 9.49 Time/ms (e) Explain how the capacitor causes the voltage across the resistor to vary with time in the way that you have drawn. The charging of the capacitor by the power supply and the discharging of the capacitor ……………………………………………………………………………………………… through the resistor will smooth the output. ………………………………………………………………………………………………3. A student wants to build a simple lift motor control system which operates using two buttons, A and B for a two-storey building. A: Up button B: Down button The lift motor only activates when someone presses any one of the buttons. Figure 9.50 shows the circuit that can be used to activate the motor. 12 V Logic gate A X 240 V B Relay switch Motor 0V Figure 9.50 Keys: Buttons A and B : When pressed, logic “1” Not pressed, logic ”0” X Output : Motor is activated, logic “1” 27
28. 28. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (a) The truth table below shows the operations of the logic gates in a lift motor control system. Input Output A B X 0 0 0 0 1 1 1 0 1 1 1 0 (i) Using the keys given, complete the truth table. (ii) Name the logic gate in the circuit in the figure 9.50. AND Gate ………………………………………………………………………………… (iii) In the space below, draw the logic gate symbol in 3(a)(ii). (b) Why is a relay switch needed in the circuit? Activates large current in the main secondary circuit supply// small current ……………………………………………………………………………………………… at the output cannot activate the motor. ……………………………………………………………………………………………… (c) The door of the lift is fitted with a light transmitter and a detector which is a light dependent resistor, LDR. If the light dependent resistor detects light, the relay switch is activated and the lift door will close. Figure 9.51 shows an electronic circuit for the control system of the lift door. Figure 9.51 240 V Motor R 28
29. 29. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (i) State the relationship between the resistance and the intensity of light received by the light dependent resistor, LDR. The higher the light intensity, the lower the resistance of the resistor. ………………………………………………………………………………… ………………………………………………………………………………… (ii) Complete the circuit in figure 9.51 by drawing the resistor and the light dependent resistor using the symbols given below. Resistor Light dependent resistor (iii) Explain how the circuit functions. – High light intensity produces lower resistance and high base voltage ………………………………………………………………………………… - A bigger base current flows and activates the transistor ………………………………………………………………………………… - A big collector current flows through the relay switch and activates the ………………………………………………………………………………… circuit of the door motor. ………………………………………………………………………………… ………………………………………………………………………………… 29
30. 30. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: ElectronicsPart C: Essay Questions1. (a) The diode, bulb and battery in circuit X and circuit Y of figures 9.52 and 9.53 are identical. Figure 9.52 Figure 9.53 (i) What is meant by a direct current and an alternating current? [2 marks] (ii) Using Figures 9.52 and figure 9.53, compare the connection of the diodes and the conditions of the bulbs. Relating the connection of the diodes and the conditions of the bulbs, deduce the function of a diode. [5 marks] (iii) State the use of a diode. [1 mark] (b) A semiconductor diode is made by joining a p-type semiconductor with a n-type semiconductor. Describe and explain the production and the characteristics of a p-type semiconductor and a n-type semiconductor. [4 marks]2. Figure 9.55 shows four circuits W, X, Y and Z, each has an ideal transformer and the circuit are used for the purpose of rectification. Circuit W Circuit Y Circuit X Circuit Z 30
31. 31. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics (i) What is meant by rectification? [1mark] (ii) Explain the working principle of a transformer. [3 marks] (iii) You are asked to make a 12 V battery charger. Study the circuits W, X, Y and Z in figures 9.55 and consider the following aspects: Type of transformer The number of turns in the primary coil and in the secondary coil. Type of rectification Characteristics of output current Explain the suitability of the above aspects and hence, determine the most suitable circuit to make the battery charge. [6 marks]3. A student carries out an experiment to determine the relationship between the collector current IC to the base current IB of a transistor. R1 = 1kΩ A2 IC R2 = 56kΩ IB 6V A1 T R3 = 2kΩ Figure 9.56 Transistor T is connected to fixed resistor R1 =1kΩ and R2 = 56 kΩ and a rheostat R3 as shown in figure 9.56. The battery supplies a voltage of 6 V to the transistor circuit. Rheostat R3 is adjusted until the current IB detected by microammeter A1 is 10 µA. The collector current, IC recorded by miliammeter A2 is shown in figure 9.57(a). 2 3 1 4 0 5 mA (a) IB = 10µA 31 31
32. 32. JPN Pahang Physics Module Form 5 Student’s Copy Chapter 9: Electronics Rheostat R3 is then adjusted to lower value so that microammeter A1 gives IB = 20 µA, 30 µA, 40 µA, 50 µA and 60 µA. The corresponding readings of IC on miliammeter, A2 are shown in figure 9.57(b), 9.57(c), 9.57(d), 9.57(e) and 9.57(f). 2 3 2 3 1 4 1 40 5 0 5 mA mA (b) IB = 20µA (b) IB = 30µA 2 3 2 3 1 4 1 40 5 0 5 mA mA (c) IB = 40µA (d) IB = 50µA 2 3 1 4 0 mA 5 (e) IB = 60µA 32 32
33. 33. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics(a) For the experiment described identify… The base current, IB (i) the manipulated variable : ..……………………………… (ii) The collector current, IC the responding variable : ……………………………….. (iii) the fixed variable The supply voltage : ………………………………..(b) From the figure in 9.57, record the collector current, IC when IB = 10, 20, 30, 40, 50 and 60µA. Tabulate your results for IB and IC in the space given below. IB/µA IC/mA 10 0.8 20 1.6 30 2.4 40 3.1 50 3.9 60 4.8(c) On a graph paper, draw a graph of IC against IB.(d) Based on your graph, determine the relationship between IC and IB. Ic is directly proportional to IB ………………………………………………………………………………………………4. Figure 9.58 shows a microphone connected to a power amplifier. When the microphone has detected a sound, an amplified sound is given out through the loudspeaker. The sound becomes louder if the volume of the amplifier is turned on to increase the power. Power amplifier Loudspeaker Volume control Microphone Figure 9.58 33
34. 34. JPN Pahang Physics Module Form 5Student’s Copy Chapter 9: Electronics Using the information based on the observation of the brightness of the bulbs, (a) Make one suitable inference. (b) State one appropriate hypothesis that could be investigated. (c) Design an experiment to investigate the hypothesis stated in (b). Choose suitable apparatus such as a diode, rheostat and others. In your description, state clearly the following: (i) Aim of the experiment, (ii) Variables in the experiment, (iii) List of apparatus and materials, (iv) Arrangement of the apparatus, (v) The procedure of the experiment, which includes the method of controlling the manipulated variable and the method of measuring the responding variable, (vi) The way you would tabulate the data, (vii) That way you would analyse the data. 34