Lecture notes Digital Electronics

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ANALOGUE AND DIGITAL ELECTRONICS TEACHING NOTES Joaquim Crisol Llicència D, Generalitat de Catalunya NILE Norwich, April of 2011 Electronics 1- Introduction to electronics. 1.1 Electricity and electronics. 30 min Classroom unit1.pps Before you start with Activity 1 you can show and comment on slide 1 with a mindmap of the contents of the 3 units. Activity 1 Individual, warm-up unit1.pps (2,3)  Show slide 2 for activity 1. Students should know these words from previous courses.  Give them time to write the answers in pencil in their workbooks.  Ask some students for the answers. With an IWB some of them can write them on the ppt.  Finally show the answers on slide 5. Let them check their answers. K1 Do you know the names of these objects? Light bulb Mp3-player Hair dryer Television Radio Computer (Electric) fan Drill Activity 2 Individual unit1.pps(4,5)  Show slide 3 with the definitions of electrical and electronic technology.  Let the students guess and fill in the blanks.  Ask some students for the answers. With an IWB some of them can write them on the pps.  Finally click on the pps to show the right answers Teaching notes Page 9 Electronics 1- Introduction to electronics. K2 Complete the definitions of electronic and electrical technology. Electrical technology energy Electronics Electronics is the branch of science and technology that deals with electrical circuits applied to information and signal processing. Electrical technology deals with the generation, distribution, switching, storage and conversion of electrical energy. Activity 3 Individual, pairs unit1.pps(6,7)  Show slide 6 with the empty table to classify objects from exercise 1 according to definitions given in exercise 2.  Let students check their answers orally with their partners using the scaffolding.  Finally ask any of them for the answers and check with slide 7. K3 Classify the objects from the first activity as electrical or electronic. Electrical Light bulb Hair dryer (Electric) fan Drill Electronic Mp3-player Radio Computer Television 1.2 Past, present and future of electronics. 60 min Classroom unit1.pps, u1a7.mp3, video from youtube Individual unit1.pps(8,9) Activity 4  Show slide 8 to triple match name, picture and definition. Tell students those three developments have been very important in the evolution of electronics.  You can ask some of them for their answers and why they have guessed that.  Show the right answers in slide 9. Reassure them that they are going to read more about those objects in next activity. Teaching notes Page 10 Electronics 1- Introduction to electronics. K4 Match these pictures with their names and definitions. A miniaturized electronic circuit Transistors manufactured on a substrate of semiconductor material. A device used to amplify and switch electrical signals by Integrated controlling the movement of circuits electrons in a low-pressure tube. A solid semiconductor device used to amplify and switch Vacuum tubes electronic signals. Activity 5 Individual unit1.pps(10,11,12,13)  Tell students to read the text by themselves in their workbooks.  It may be necessary to explain some words they don’t understand. For that you have the text on slides 10 and 11.  Then tell them they should search, highlight and transfer the information they are asked for in the activity and draw the time line.  Finally, you or a student can do the activity on the IWB (slide12) or directly show the answers on slide 13. K5 Find out what year these things happened by reading the text below. a) 1904 Invention of the vacuum tube. d) 1920 Start of radio broadcasting. b) 1947 Invention of the transistor. e) 1947 Start of black and white television.. c) 1960 First microchip. f) _ _ _ _ First mobile phone in your family. Place them on the timeline. a) d) b) e) c) f) 1900 1920 1940 1960 1980 2000 Teaching notes Page 11 Electronics 1- Introduction to electronics. Individual, check in pairs unit1.pps(14,15) Activity 6  Students should read the text in depth individually to fill in the table.  Let them write answer sentences as in the model. They should practice these sentences when checking answers with their partner. There is not a closed answer for the applications.  Ask some students for the answers orally. You can show the proposed answers on slide 15. K6 Fill in the gaps with data from the text above. Date Invention Applications 1904 Vacuum tubes To amplify electric signals 1947 Transistor To amplify electric signals 1960 Integrated circuit Microcomputers, mobile phones Activity 7 Individual, whole group unit1.pps(16,17,18), u1a7.mp3, youtube  This is quite an open and creative activity for the students. The purpose is to create awareness and discussion more than getting the right answer.  Let them see the two following pictures (16) and read the questions.  Then you should play the audio file or read the text below one or two times.  At this point they should answer questions a), b) and c).  Now, show the video from Greenpeace (link on slide 16) before asking them to write proposals for question d). It can also be done without the video.  Use slides 17 and 18 to answer the questions. For question d) you can have a debate. Let students explain proposals to the whole group and finally try to reach an agreement to choose the best ones. Teaching notes Page 12 Electronics 1- Introduction to electronics. Text to read or play: The world is consuming more and more electronic products every year. This has caused a dangerous explosion in electronic scrap (e-waste) containing toxic chemicals and heavy metals that cannot be disposed of or recycled safely. But this problem can be avoided. Every year, hundreds of thousands of old computers and mobile phones are dumped in landfills or burned. Thousands more are exported, often illegally, from Europe, the US, Japan and other industrialized countries, to Asia and Africa. There, workers at scrap yards, some of whom are children, are exposed to a cocktail of toxic chemicals and poisons. Optional video: http://video.google.com/videoplay?docid=5944615355863607664 K7 Look at these pictures and listen to the text. Then answer the questions below. a) What is e-waste? E-waste is old electronic rubbish. b) Where does most e-waste go? Most e-waste is exported to poor countries in Asia and Africa. c) Do you think e-waste is toxic? I think it is toxic because electronic products contain heavy metals such as lead and mercury and hazardous chemicals. d) E-waste will be a bigger problem in the future because more and more people use more and more electronic devices and change them more often. Talk to your partner and try to find a solution to the e-waste problem.  Governments should ... (open answer)  We all should ...(open answer)  Electronic products should ... (open answer) 1.3 From analogue to digital electronic systems. 90 min Classroom unit1.pps , worksheets 1A 1B Individual, pairs, class. unit1.ppt (19,20,21,22,23) Activity 8  Show slide 19 and explain how we can represent electronic systems with block diagrams.  Tell students to label the objects, identify the blocks and explain them using the word and sentence bank below. (slides 20, 21)  After that they have to practice explaining the diagrams with their partners following the model. Assess some of them individually.  Check the answers (slide 22, 23) and make a few of them explain the diagrams.  Correct grammar and pronunciation. Other students can give their own feedback. Teaching notes Page 13 Electronics 1- Introduction to electronics. K8 Label the objects by using the language bank below and identify the input and output block for each one. Process Input Output MICROPHONE ELECTRONICS LOUDSPEAKER It converts sound to It processes It converts electrical signals electrical signals electrical signals to MEGAPHONE sound. RADIO ELECTRONICS LOUDSPEAKER AERIAL It takes in It processes Transforms electromagnetic electrical signals. electrical signals to waves and produces sound. an electrical signal. TEMPERATURE TEMPERATURE ELECTRONICS DISPLAY SENSOR It senses changes in It processes It gives a readout of DIGITAL temperature and electrical signals. temperature. THERMOMETER produces an electrical signal. DISPLAY KEYPAD ELECTRONICS SCREEN Push-buttons that It processes It converts electrical signals electrical signals to generate electrical CALCULATOR visible numbers signals. Activity 9 Individual unit1.pps(24,25,26)  Read aloud and explain slide 24 about analogue, digital and binary signals. Explain vocabulary if needed.  Next, students should transfer the information and label the four signals on slide 24 and justify their decision matching the three sentences below.  Read the solutions on slide 26 and clarify any doubts before moving on. Teaching notes Page 14 Electronics 1- Introduction to electronics. K9 Label these signals as analogue, digital or digital binary. signal analogue signal analogue d. binary digital time time The dashed signal is digital binary because it has any value. The continuous signal is analogue because it has only two values The dotted signal is digital because it has only certain values. Activity 10 Individual, pairs, group unit1.pps(27,28)  Show slide 27 and ask students to label the three objects and classify them in the Venn diagram according to the last slide.  Then make them check answers orally with their partner using the model.  Ask three of them for the answers. Check with slide 28.  Now, give them some time to add a new example of each in the Venn’s diagram. Check some of them with the whole group. K10 We can think of objects as analogue or digital. Can you write the names of the following objects in the diagram? digital analogue 2) 1) 2) display 1) binary thermometer 3) 3) switch Teaching notes Page 15 Electronics 1- Introduction to electronics. Individual, pairs, group unit1.pps(29,30,31,32), worksheets 1A, 1B Activity 11  Show slide 29 with the gapped text for the activity. Ask students to read it on the screen or on their workbooks.  Make them work in pairs with an A member and a B member. Hand out worksheets A and B.  Individually, they have to copy text A or B into their workbooks.  After that they have to dictate the text they have copied to each other.  Next, they have to read the whole text and agree on a heading. At this point they may ask for some vocabulary.  Show slide 30 with the whole text. Listen to some proposals or the heading and agree on one.  Move on to slide 31. Ask them to draw what they think is the original signal without noise individually and complete the sentence below the signals.  Ask some of them to draw them on the IWB. Demonstrate that there are many possibilities for the analogue signal and what that means. K11 Mutual dictation: HEADING: Advantages of digital signals and noise. (a) Signals in nature are analogue. For example, sound is an air pressure wave . It is analogue because it can be any value. (b) Digital signals have many advantages : (a)  They can be converted to numbers and easily processed by computers .  They are easy to store and to compress using mathematical algorithms. (b)  Noise does not affect them as much as to analogue signals. When data is transmitted, processed or stored a certain amount of NOISE enters into (a) the signal . (b) With an analogue signal, noise cannot be distinguished from the original signal . We have distortion. In a digital signal, noise will not matter, as any signal close enough to a particular value will be interpreted as that value. Draw the original signal in colour. Which one is more difficult to rebuild? ? time time The digital binary signal is easier to reproduce because it can have only two values. Teaching notes Page 16 Electronics 1- Introduction to electronics. Individual unit1.pps(32,34,35,36), u1a12.mp3 Activity 12  Show gapped text on slide 32. Play the audio file or read aloud the complete text. Students have to fill in the gaps.  Explain and respond to questions about the text.  Show slide 35 with the 4-option question and ask them to choose one and give reasons for it.  Get answers from some students. Contrast them with the input text. Finally show the right answer and the explanatory diagram on slide 36. K12 Listen to the text about the analogue-digital conversion process. Fill in the gaps and answer the final question. Analogue signals are processed by analogue circuits and digital signals are processed by digital circuits. In between, we can use these electronic circuits to convert from analogue to digital and vice versa.  ADC: analogue-to-digital converters  DAC: digital-to-analogue converters …001010101010111111…. Digital Analogue Analogue PROCESS ADC DAC INPUT OR OUTPUT STORAGE For example, we can get sound with a microphone and analogue electronics. Then an ADC converts this signal to digital data. This data can be processed and stored in a digital format, such as mp3. Home electronics used to be analogue but nowadays everything is mainly digital. So, we have digital TV, digital photography, digital audio, etc. Circle the right answer: a) DAC stands for analogue-digital-conversion. b) Modern electronics is mostly digital. c) To play mp3 music we have to use a DAC. d) Sound is a digital signal. …001010101010111111…. Analogue Digital mp3 DAC OUTPUT music Teaching notes Page 17 Electronics 1- Introduction to electronics. Individual unit1.pps(37,38) Activity 13  This activity is intended to check understanding of texts in activities 11 and 12.  Students have to read all the statements, decide if they are true or false. In the second case, they have to produce the right statement. Use slide 37.  Go through each sentence and reason the answer with the participation of some students.  Show the corrected activity on slide 38. K13 Decide if these sentences are true or false. If they are false change them so that they are true. T / F A cassette tape is the digital evolution of a CD (compact disc). A CD is the digital evolution of a cassette tape. T / F DVB (digital video broadcasting) has no noise because it is an analogue signal. DVB has no noise because it is a digital signal. T / F Analogue photography can be easily modified, compressed and transmitted. Digital photography can be easily modified, compressed and transmitted. T / F An ADC converts digital signals to analogue. An ADC converts analogue signals to digital. T / F Digital electronic systems are older than analogue systems. Digital electronic systems are newer than analogue systems. T / F All digital signals are binary signals. All binary signals are digital signals. Individual unit1.pps(39) SELF ASSSESSMENT  Show the self assessment table and ask students to fill it in.  If they answer NO to some question they should revise the exercises at home.  Assign a few minutes at the beginning of next lesson to answer possible questions. More or QUESTION No Yes less Can I order the main developments in electronics and say what decade they happened? Do I know what problems e-waste can cause and how to avoid them? Can I draw a block diagram for a basic electronic system? Can I give examples of analogue, digital and binary signals? Can I compare analogue and digital systems? Teaching notes Page 18 Electronics 2- Analogue electronics. 2 ANALOGUE ELECTRONICS. 6 h Classroom, workshop unit2.pps, electronic kit Slides for unit 2: 1. Title. 47. 7a: sequence charge and discharge. 2. 1a: magnitudes. 48. 7a: answers. 3. 1a: answers. 49. Time constant graph. 4. 1b: Ohm’s law, formulations. 50. 7b: time constant calculations. 5. 1b: answers. 51. 7b: answers. 6. 1c: Ohm’s law, proportionality. 52. 7c: describe charge and discharge. 7. 1c: answers. 53. 7c: answers. 8. 1d: Ohm’s law, graphs. 54. Introduction to diodes. 9. 1d: answers. 55. 8a, 8b: basic questions. 10. 2a: Ω multiples. 56. 8a, 8b: answers. 11. 2a: answers. 57. 8c: draw wires on a circuit picture. 12. 2b: calculations (1). 58. 8c: answers. 13. 2b: answers. 59. How to calculate forward current. 14. 2b: calculations (2). 60. 9: calculate the current (1). 15. 2b: answers. 61. 9: answers (1). 16. 3a: colour code, blanks. 62. LED theory. 17. 3a: answers. 63. 10: current calculation. 18. 3b: resistor values. 64. 10: answers. 19. 3b: answers. 65. 11a: reason double polarisation. 20. Tolerance. 66. 11a: answers. 21. 3c: max/min resistance. 67. 11b: rectifier bridge design. 22. 3c: answers. 68. 11b: answers. 23. 3d: propose resistors. 69. 12a: transistor (blanks 1). 24. 3e: describe resistor. 70. 12a: transistor (blanks 2). 25. 4a: variable resistors. 71. 12a: answers 1. 26. 4a: answers. 72. 12a: answers 2. 27. Special resistors table. 73. 12b: gain calculations. 28. 4b: explain special resistors. 74. 12b: answers. 29. 4b: answers. 75. 12c: base current calculation. 30. 4c: visual classification. 76. 12c: answer. 31. 4c: answers. 77. 13a: how to control Ic. 32. Voltage dividers. 78. 13a: answers. 33. 5a: voltage divider calculation. 79. 13b: current amplifier. 34. 5a: answers. 80. 13b: answers. 35. 5b: predicting voltage divider. 81. Transistor as a digital switch. 36. 5b: answers. 82. 14a: Identify circuit. 37. 5c: potentiometer in a voltage div. 83. 14a: answers. 38. 5c: answers. 84. 14b: describe timer. 39. 6a: capacitors blank fill. 85. 14b: answer. 40. 6a: answers. 86. Self assessment. 41. 6b: Farad and submultiples. 87. Circuit 1: bridge rectifier. 42. 6b: answers. 88. Circuit 1 with values. 43. Text on types of capacitors. 89. Circuit 2: light regulator. 44. 6c: questions on types of capacitors. 90. Circuit 2 with values. 45. 6c: answers. 91. Circuit 3: timer. 46. RC for timing purposes. 92. Circuit 3 with values. Teaching notes Page 19 Electronics 2- Analogue electronics. 2.1 Resistors. 3 h Classroom unit2.pps, some real resistors. Activity 1a Individual unit2.pps (2,3)  Students should know the symbol of a resistor, the four electric magnitudes and their units from previous school years. The purpose of this activity is to remind them of that and to introduce English vocabulary as a warm-up.  Ask them to fill in the table on slide 2. You can to draw a basic circuit to remind them.  Show answers on slide 3. Check spelling and pronunciation with them. K1a Remember the main electrical magnitudes and find the unit for each one. Magnitude Unit Voltage (V) Volts (V) Electric current (I) Ampere (A) Power (P) Watt (W) Electric resistance (Ω) Ohms (Ω) Activity 1b Individual unit2.pps (4,5)  Students already learnt Ohm’s law in previous years. Now they should understand it better. For that, they need the vocabulary to express formulas.  Show slide 4 and read the formulae: “V equals I by R”, “I equals V over R”. Give them time to match the four descriptions to one of the formulae.  Ask some of them to read their answers before showing the key on slide 5. OHM’S LAW connects resistance, voltage and current in an electrical circuit. There are many ways to express this relationship: with text, with formula and graphically. a) Formula for finding the voltage across a resistor for a given current. b) Formula for finding the current through a resistor for a given voltage. K1b Which formula represents these formulations of Ohm’s law better, a) or b)? a The voltage (V) across a resistor is proportional to the current (I) passing through it, where the constant of proportionality is the resistance (R). b When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. a Voltage across a resistor equals the current through it multiplied by the resistance. b Current through a resistor equals the voltage across it divided by the resistance. Teaching notes Page 20 Electronics 2- Analogue electronics. Individual unit2.pps (6,7) Activity 1c  In this short activity students learn the language to express magnitude dependence.  Show slide 6 with the activity. Make it clear that more than one can be right.  Check answers with slide 7.  You can ask them for some more examples using the same grammatical structure. K1c Choose the right answer or answers (a and c). a) The higher the resistance, the lower the current. b) The higher the resistance, the higher the current. c) The lower the resistance, the higher the current. d) The lower the resistance, the lower the current. Activity 1d Individual unit2.pps (8,9)  Explain to students that graphs are very important to understand electronics.  Show slide 8 and ask them to identify the resistor for each graph without calculations. They just have to apply the relationships they have learnt. You can suggest that they write down the formula that explains each graph (I=V/R and V=R·I).  Ask some students describe the graphs for the whole class with the help of the substitution table and check at the same time the resistor values. Answers are on slide 9. K1d In this circuit, R can be 0.5 Ω, 1 Ω or 2 Ω. Identify which resistance corresponds to each graph. I V R= 0.5 Ω R= 2 Ω I R= 1 Ω R= 1 Ω + R V R= 2 Ω R= 0.5 Ω _ V I a) b) Construct a sentence that makes sense for graph a) and one for graph b). a) The higher the resistance the lower the current for a given voltage. b) The higher the resistance the higher the voltage for a given current. The lower the lower the current voltage. the resistance, for a given The higher the higher the voltage current. Teaching notes Page 21 Electronics 2- Analogue electronics. Individual unit2.pps (10,11) Activity 2a  Compare the use of multiples for resistance with the use of multiples for distance with m.  Explain the examples and get students do the first part of the activity on slide 10.  Check answers with slide 11. Check pronunciation for k and M.  Focus on numbers first. Just when they manage the conversion you should move to writing numbers in the second part of the activity. K2a Give the value in Ω for the following resistors. a) 6k8 = 6,800 Ω b) 1M2 = 1,200,000 Ω c) 47R = 47 Ω d) 5R6 = 5.6 Ω Write the answers like this: 5M6: five point six mega-ohms are five million six hundred thousand Ω. a) 6k8: six point eight kilo-ohms are six thousand eight hundred Ω. b) 1M2: one point two mega-ohms are one million two hundred thousand Ω. c) 47R: forty-seven Ω. d) 5R6: five point six Ω. Activity 2b Individual, pairs. unit2.pps (12, 13, 14, 15)  Explain the submultiples of the Ampere. The distance example for m and mm usually works.  Make students aware of the different use of . and , for grouping numbers and for decimal position in Anglo-Saxon countries.  Let them do the calculations and check results or procedure with their partners. Remind them to be careful with the use of “ ,” or “.” in their calculators.  You or some student should do and explain the activity step by step on slides 12 and 13. You can use slides 14 and 15 to check results too. K2b Now apply Ohm’s law to calculate the current through the resistors as in the example. When you finish, check the answers with your partner without reading their workbook. I? + 5M6 5V Remember: 0.001 A = 1 mA and 0.000001 A = 1µA Teaching notes Page 22 Electronics 2- Analogue electronics. a) I? + 6k8 5V b) I? + 1M2 5V c) I? + 47R 5V d) I? + 5R6 What result did you get for part a)? 5V Activity 3a Individual unit2.pps (16, 17), some resistors  Students should get the missing words from the table without further explanations. Just show them some resistors to see how the real colour code is printed on them. They will understand it better when they use it in the next activities.  Read the text on slide 17 yourself or have some students to read it to check pronunciation. K3a Fill in the blanks looking at the table below. A lot of resistors have coloured rings on them instead of numbers. Each colour stands for a different unit: black is zero, brown is one, red is two; orange is three; yellow is four; green is five; blue is six; violet is seven; grey is eight; white is nine, as you can see in the table below. The first band is for tens and the second band for units. The third band is the multiplier. Example: red / violet / green stands for 2 / 7 / 00000, that is 2700000 Ω or 2.7 MΩ. Teaching notes Page 23 Electronics 2- Analogue electronics. st nd 1 colour band 2 colour band Multiplier Tolerance Black 0 Black 0 Silver divide by 0.01 Silver 10% Brown 1 Brown 1 Gold divide by 0.1 Gold 5% Red 2 Red 2 Black multiply by 1 Red 2% Orange 3 Orange 3 Brown multiply by 10 Yellow 4 Yellow 4 Red multiply by 100 Green 5 Green 5 Orange multiply by 1,000 Blue 6 Blue 6 Yellow multiply by 10,000 Violet 7 Violet 7 Green multiply by 100,000 Grey 8 Grey 8 Blue multiply by 1,000,000 White 9 White 9 Activity 3b Individual unit2.pps (18,19)  In this activity students are going to get the value of a resistor without the tolerance. It is quite easy for them just looking at the examples and at the colour table.  Point out that colour black in the multiplier band means adding nothing.  Early finishers can explain the code to those who have difficulties.  Finally show slide 19 with the answers and read some values. K3b Obtain the value of these resistors: a) Brown / green / red: 1/5/00= 1,500 Ω = 1.5 kΩ b) Orange / orange / brown: 3/3/0= 330 Ω c) Green / grey / yellow: 5/8/0000= 580,000 Ω = 580 kΩ d) Yellow /violet / orange: 4/7/000= 47,000 Ω = 47 kΩ Express the previous values with M or k if possible. For example 27000 Ω= 27 kΩ Activity 3c Individual unit2.pps (20, 21, 22)  Explain the reasons for a tolerance band and how to calculate the maximum and minimum value for a resistor using slide 20.  Now students have to calculate the maximum and minimum value for the four resistors in activity 3b. Remind them to be careful with the decimal point and not to forget the unit when they fill in the table on slide 21.  Do some calculations for the whole class or show slide 22 with the answers. K3c Manufacturers of the resistors cannot guarantee the exact value. The fourth band expresses the TOLERANCE in %. With the tolerance we can calculate the minimum and maximum real values for the four resistors below as in the example: Red /violet / orange //silver R =27000 Ω ±10% 10% of 27000 = 27000·10/100=2700 R = 27000 Ω ± 2700 Ω Minimum value =27000-270=26730 Ω Maximum value = 27000+270=27270 Teaching notes Page 24 Electronics 2- Analogue electronics. Colours Value Tol. % Tol. Minimum Maximum Red /violet / orange //silver 27000 Ω 10% 2700 26,730 Ω 27,270 Ω Brown / green / red // silver 1500 Ω 10% 150 1,350 Ω 1,650 Ω Orange / orange / brown // gold 330 Ω 5% 16.5 313.5 Ω 346.5 Ω Green / grey / yellow // silver 580000 Ω 10% 58000 522,000 Ω 638,000 Ω Yellow /violet / orange // gold 47000 Ω 5% 2350 44650 Ω 49,350 Ω Pairs unit2.pps (23) Activity 3d  Explain that resistor values come in preferred series values.  Show them the activity and the sample dialogues for the activity on slide 23.  Assess the groups as they produce the colour codes and dialogues. K3d Work with your partner in turns. Choose 1 resistor from the pool and write down its colours. Then you have to tell your partner the colours and he has to find out the value. 330 kΩ 1kΩ 680 kΩ 1.8 MΩ 2200 Ω 1.5 kΩ 270 Ω 8.2 kΩ 1.2 kΩ 120Ω 270 kΩ 18 Ω 3.3 MΩ 390 Ω 820 Ω 5.6 kΩ 47 kΩ 4700 kΩ - My resistor is brown, black, red. - Is it 1000 Ω? - Yes, it is. You are right… - My resistor is … Activity 3e Individual or pairs, class unit2.pps (24), real resistors  This is a summary activity on resistors. Show students slide 24 with the model for describing a real resistor. Students can work individually or in pairs.  When they finish ask a few of them one by one to describe the resistor. The rest of the class must check the answer and report if they find any mistake. You can use this activity for assessment. k3e Your teacher will give you one real resistor. Note down the colours, calculate its value and write the text to describe your resistor to the class. Teaching notes Page 25 Electronics 2- Analogue electronics. The first band colour of my resistor is...... The quoted value is .......................... The tolerance is... The minimum….. Activity 4a class unit2.pps (25,26), some potentiometers  Explain how potentiometers are and work using some real ones.  Do the activity orally with the whole group to check understanding. Answers are on slide 26.  Make them copy results into their workbook. K4a Can you get the values for R in these 10 kΩ potentiometers? CB A A A 2 k 5 k 8 k C 10k 10k C 10k C 5 k 8 k 2 k B B B Activity 4b Individual unit2.pps (27, 28, 29)  Show slide 27 with the special resistors table. Explain what “coefficient” means using the language students learnt for Ohm’s law: the higher, the lower...  Show activity on slide 28. Let them write the explanations for PTC and LDR.  Have some of them read their answers and compare results with slide 29. K4b Explain how the special resistor works as in the model:  NTC thermistors’ resistance changes according to the temperature. As temperature goes up, the resistance goes down. They are used in temperature-sensing circuits.  PTC thermistors resistance changes according to the temperature. As temperature goes up, the resistance goes up. They are used in temperature- sensing circuits.  LDR’s resistance changes according to light. As light is brighter, the resistance goes down. They are used in light-sensing circuits. Teaching notes Page 26 Electronics 2- Analogue electronics. Activity 4c Individual unit2.pps (30,31)  Show empty diagram on slide 30. Let students fill in the blank from their knowledge or look for the names from previous activities.  Use slide 31 in combination with previous slides to show the finished diagram and where information is. You can round-up with some questions as - What’s the difference between a fixed resistor and a potentiometer? - What’s the difference between the symbol of a LDR and a variable resistor? K4c Complete the visual organizer. - Fixed resistors. - Variable or potentiometers. - Resistors - NTC thermistors + - Special resistors - PTC thermistors - LDR’s Individual unit2.pps (32, 33, 34) Activity 5a  Explain how and why we use resistors in potential dividers with slide 32.  I suggest deducing the formula to review Ohm’s law and series resistor association.  Use slide 32 to show the voltage divider they have to solve. Preferably, they have to do it without a calculator.  The key is on slide 34. K5a Calculate Vout by applying the formula of a voltage divider. I Vin= 9V R1=20Ω + R2=10Ω Vout Teaching notes Page 27

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