ect1501 - gimmenotes · 5.2 voltage in parallel circuits 5.3 kirchhoff’s current law 5.4 total...
TRANSCRIPT
ECT1501/101/3/2018
Tutorial Letter 101/3/2018
Electronics I Theory
ECT1501
Semesters 1 and 2
Department of Electrical and Mining Engineering
This tutorial letter contains important information
about your module.
BARCODE
2
CONTENTS
Page
1 INTRODUCTION .......................................................................................................................... 3
2 PURPOSE OF AND OUTCOMES FOR THE MODULE............................................................... 3
2.1 Purpose ........................................................................................................................................ 3
2.2 Outcomes ..................................................................................................................................... 3
3 LECTURER(S) AND CONTACT DETAILS ................................................................................... 3
3.1 Lecturer(s) .................................................................................................................................... 3
3.2 Department ................................................................................................................................... 4
3.3 University ...................................................................................................................................... 4
4 MODULE-RELATED RESOURCES ............................................................................................. 4
4.1 Prescribed books .......................................................................................................................... 4
4.2 Recommended books ................................................................................................................... 4
4.3 Electronic Reserves (e-Reserves) ................................................................................................. 4
4.4 Library services and resources information ................................................................................... 4
5 STUDENT SUPPORT SERVICES ................................................................................................ 5
6 STUDY PLAN ............................................................................................................................... 5
7 PRACTICAL WORK AND WORK-INTEGRATED LEARNING ..................................................... 8
8 ASSESSMENT ............................................................................................................................. 8
8.1 Assessment criteria ....................................................................................................................... 8
8.2 Assessment plan .......................................................................................................................... 8
8.3 Assignment numbers .................................................................................................................... 9
8.3.1 General assignment numbers ....................................................................................................... 9
8.3.2 Unique assignment numbers ........................................................................................................ 9
8.4 Assignment due dates .................................................................................................................. 9
8.5 Submission of assignments .......................................................................................................... 9
8.6 The assignments ........................................................................................................................ 11
8.7 Other assessment methods ........................................................................................................ 39
8.8 The examination ......................................................................................................................... 39
9 FREQUENTLY ASKED QUESTIONS ........................................................................................ 39
10 SOURCES CONSULTED ........................................................................................................... 39
11 CONCLUSION ............................................................................................................................ 39
12 ADDENDUM ............................................................................................................................... 39
ECT1501/101/3/2018
3
1 INTRODUCTION
Dear Student
Welcome to the subject Electronics I (ECT1501) at UNISA. This tutorial letter serves as a guideline to this course. It provides you with general administrative information as well as specific information about the subject. Read it carefully and keep it safe for future reference. We trust that you will enjoy this course.
2 PURPOSE OF AND OUTCOMES FOR THE MODULE
2.1 Purpose
The purpose of this module is to enable students develop competencies and skills in solving problems in DC and AC circuits. Students will be exposed to the operation of various electronic components, such as resistors, capacitors, inductors, transformers, diodes, etc. and learn how to test them.
2.2 Outcomes
Apply knowledge of mathematics, physical science and engineering fundamentals to
identify and solve problems through accurate calculations and measurements of basic SI
units and dimensions as used in engineering.
Solve basic electronics engineering problems using Ohm’s Law and Kirchoff’s Laws.
Apply and explain the fundamentals of reactive components in reactive (RLC) circuits.
Apply and explain the operation of transformers and their application in electronic circuits.
Design both half-wave and full-wave rectifier circuits.
3 LECTURER(S) AND CONTACT DETAILS
3.1 Lecturer(s)
Dr. KA Ogudo e-mail : [email protected] 011 471 2728
M. Dockrat Tutor Marker email: [email protected] phone: 0825625530
Mr. R Myataza Tutor Marker
e-mail : [email protected]
Tel numbers 076 2241 647 & 083 3999 311
Contact Times: Mon. – Fri: 18h00-21h00
4
3.2 Department
Department of Electrical and Mining Engineering: electrical&[email protected]
3.3 University
If you need to contact the University about matters not related to the content of this module, please consult the publication My studies @ Unisa that you received with your study material. This brochure contains information on how to contact the University (e.g. to whom you can write for different queries, important telephone and fax numbers, addresses and details of the times certain facilities are open).Always have your student number at hand when you contact the University.
4 MODULE-RELATED RESOURCES
4.1 Prescribed books
Electronic Fundamentals, FLOYD TL
ISBN.: 5 0130852368 (or Newest Edition)
4.2 Recommended books
There are no recommended books for this module.
4.3 Electronic Reserves (e-Reserves)
There are no electronic reserves for this module.
4.4 Library services and resources information
For brief information, go to www.unisa.ac.za/brochures/studies
For detailed information, go to the Unisa website at http://www.unisa.ac.za/ and click on
Library.
For research support and services of personal librarians, go to
http://www.unisa.ac.za/Default.asp?Cmd=ViewContent&ContentID=7102.
The Library has compiled numerous library guides:
finding recommended reading in the print collection and e-reserves –
http://libguides.unisa.ac.za/request/undergrad
requesting material – http://libguides.unisa.ac.za/request/request
postgraduate information services – http://libguides.unisa.ac.za/request/postgrad
finding , obtaining and using library resources and tools to assist in doing research –
http://libguides.unisa.ac.za/Research_Skills
how to contact the library/finding us on social media/frequently asked questions –
http://libguides.unisa.ac.za/ask
ECT1501/101/3/2018
5
5 STUDENT SUPPORT SERVICES
Important information appears in your my Studies @ Unisa brochure.
6 STUDY PLAN
Use your my Studies @ Unisa brochure for general time management and planning skills.
Program of study
TOPIC CHAPTER
1.
Demonstrate the fundamental knowledge of
common electrical components, quantities
and units.
1.1 Electrical components and measuring
instruments.
1.2 Electrical and magnetic units.
1.3 Scientific notation.
1.4 Engineering notation and Metric prefixes.
1.5 Metric unit conversions.
2.
Describe the fundamentals of voltage,
current and resistance in electric circuits.
2.1 Atoms.
2.2 Electrical charge.
2.3 Voltage.
2.4 Current.
2.5 Resistance.
2.6 The Electric circuit.
2.7 Basic circuit measurements.
2.8 Electrical safety.
3.1 Ohm’s Law
3.2 Application of Ohm’s Law
3.3 Energy and Power
3.4 Power in an Electric Circuit
3.5 The Power Rating of resistors
3.6 Energy conversions and voltage drop in a
resistance.
3.7 Power supplies.
3.8 Introduction to troubleshooting
4.1 Resistors in series
4.2 Current in a series circuit
4.3 Total series resistance
6
4.4 Ohm’s Law in series circuits
4.5 Voltage sources in series
4.6 Kirchhoff’s voltage law
4.7 Voltage dividers
4.8 Power in a series circuit
4.9 Circuit ground
4.10 Troubleshooting
3.
Demonstrate an understanding of application
of OHM’s Law to Series, Parallel and series
parallel circuits
5.1 Resistors in parallel
5.2 Voltage in parallel circuits
5.3 Kirchhoff’s current law
5.4 Total parallel resistance
5.5 Ohm’s Law in parallel circuits
5.6 Current dividers
5.7 Power in parallel circuits
5.8 Troubleshooting
6.1 Identifying series-parallel relationships
6.2 Analysis of series-parallel circuits
6.3 Voltage dividers with resistive loads
6.4 Loading effect of a voltmeter
6.5 The Wheatstone Bridge
6.9 Troubleshooting (based on 6.1 – 6.5)
4.
Explain the fundamentals of
electromagnetism
7.1 The magnetic field
7.2 Electromagnetism
7.3 Electromagnetic devices
7.4 Magnetic Hysteresis
7.5 Electromagnetic Induction
7.6 Applications of electromagnetic induction
5
Understand principles and operation of ac,
RC, rl and rlC circuits
8.1 The Sine wave
8.2 Sinusoidal voltage sources
8.3 Voltage and current values of a sine wave
8.4 Angular measurement of a sine wave
8.5 The sine wave formulae
8.6 Ohm’s Law and Kirchhoff’s Law in AC circuits
8.7 Superimposed DC and AC voltages
8.8 Nonsinusoidal waveforms
8.9 The oscilloscope
6.
Demonstrate a knowledge of capacitors
9.1 The basic capacitor
9.2 Types of capacitors
ECT1501/101/3/2018
7
9.3 Series capacitors
9.4 Parallel capacitors
9.5 Capacitors in DC circuits
9.6 Capacitors in AC circuits
9.7 Capacitor applications
9.8 Testing capacitors
10.1 Sinusoidal response of RC circuits
10.2 Impedance and phase angle of series RC circuits
10.3 Analysis of series RC circuits
10.4 Impedance and phase angle of parallel RC circuits
10.5 Analysis of parallel RC circuits
10.6 Analysis of series-parallel RC circuits
10.7 Power in RC circuits
10.8 Basic applications
10.9 Troubleshooting
7.
Demonstrate a knowledge of inductors
11.1 The basic inductor
11.2 Types of inductors
11.3 Series inductors
11.4 Parallel inductors
11.5 Inductors in DC circuits
11.6 Inductors in AC circuits
11.7 Inductor applications
11.8 Testing inductors
12.1 Sinusoidal response of RL circuits
12.2 Impedance and phase angle of series RL circuits
12.3 Analysis of series RL circuits
12.4 Impedance and phase angle of parallel RL circuits
12.5 Analysis of parallel RL circuits
12.6 Analysis of series-parallel RL circuits
12.7 Power in RL circuits
12.8 Basic applications
12.9 Troubleshooting
13.1 Impedance and phase angle of series RLC circuits
13.2 Analysis of series RLC circuits
13.3 Series resonance
13.4 Series resonant filters
13.5 Parallel RLC circuits
8
13.6 Parallel resonance
13.7 Parallel resonant filters
13.8 Applications
8.
Explain the fundamentals of transformers
14.1 Mutual inductance
14.2 The basic transformer
14.3 Step-up transformers
14.4 Step-down transformers
14.5 Loading the secondary
14.6 Reflected load
14.7 Impedance matching
14.8 The transformer as an isolation device
14.9 Practical transformers
14.10 Other types of transformers
14.11 Troubleshooting
9.
Demonstrate the fundamentals of semi-
conductors
16.1 Introduction to semi-conductors
16.2 The PN Junction diode
16.3 Diode characteristics
16.4 Diode rectifiers
16.4 Power supplies
16.5 Special purpose diodes
16.6 Troubleshooting
7 PRACTICAL WORK AND WORK-INTEGRATED LEARNING
The practical part of this module will be covered in the module ECTPRA1.
8 ASSESSMENT
8.1 Assessment criteria
Your final mark will be calculated by using a ratio of 20% year mark and 80% examination mark.
8.2 Assessment plan
You will find your assignments for this subject in this Tutorial Letter. Assignment 1 and 2 are compulsory and both assignments will be used in the calculation of your year mark. Please send the completed assignments to UNISA before the closing dates stated in this section.
The mark for Electronics I (ECT1501) is calculated as follows:
The year mark contributes to 20%.
The examination mark contributes to 80%
ECT1501/101/3/2018
9
The year mark is based on all the assignment marks obtained and their contribution towards the final year mark are as shown in the table below:
ASSIGNMENT NUMBER
CONTRIBUTION TOWARDS YEAR
MARK
1 (Compulsory) 10%
2 90%
TOTAL = 100 %
8.3 Assignment numbers
8.3.1 General assignment numbers
Assignments are numbered consecutively per module, starting from 01.
8.3.2 Unique assignment numbers
SEMESTER 1
Assignment 1: (Compulsory)
868704
Assignment 2: (Compulsory)
658899
SEMESTER 2
Assignment 1: (Compulsory)
690239
Assignment 2: (Compulsory)
673537
8.4 Assignment due dates
THE CUT-OFF SUBMISSION DATES FOR THE ASSIGNMENTS ARE :
Assignment 1: (Compulsory) Assignment 2: (Compulsory)
2 March 2018 9 April 2018
SEMESTER 2
THE CUT-OFF SUBMISSION DATES FOR THE ASSIGNMENTS ARE :
Assignment 1: (Compulsory) Assignment 2: (Compulsory)
29 August 2018 28 September 2018
8.5 Submission of assignments
ALL ASSIGNMENTS (submitted) HAVE TO BE ATTEMPTED!!!!!!! THE SUBMISSION OF AN EMPTY ASSIGNMENT COVER IS UNACCEPTABLE.
IT IS VERY IMPORTANT TO CONSIDER THE FOLLOWING POINTS :
10
NO LATE ASSIGNMENT SUBMISSIONS WILL BE ACCEPTED.
KEEP A CLEAR COPY OF THE ASSIGNMENT FOR YOUR OWN REFERENCE. THIS IS IMPORTANT, AS ASSIGNMENTS DO GET LOST.
SUBMISSIONS OF ASSIGNMENTS MUST BE IN ACCORDANCE WITH “MY STUDIES @ UNISA”.
Please note that model answers for the assignments will be dispatched to all students shortly after the closing date of the assignment. This implies that you cannot submit your assignment later than the stipulated submission date.
The model answers will be in tutorial letter 201, under additional Resources on myunisa. For detailed information and requirements as far as assignments are concerned, see the brochure my Studies @ Unisa that you received with your study material. To submit an assignment via myUnisa:
Go to myUnisa.
Log in with your student number and password.
Select the module.
Click on assignments in the menu on the left-hand side of the screen.
Click on the assignment number you wish to submit.
Follow the instructions.
ECT1501/101/3/2018
11
8.6 The assignments
SEMESTER 1
THE CUT-OFF SUBMISSION DATES FOR THE ASSIGNMENTS ARE :
Assignment 1: (Compulsory) Assignment 2: (Compulsory) Assignment 3 (Not compulsory)
2 March 2018 9 April 2018
ASSIGNMENT 1
1. How many amperes of current flows when 5 coulombs of charge flow past a given point in a wire in 2 seconds?
1. 2.5 A
2. 10 A
3. 0.4 A
4 20 A
5 50 A
2. The current – voltage relation is given bydi
v Ldt
. If the current in a 2H inductor varies at
a rate of 2A/s, find the voltage across the inductor.
1. 6 V
2. 4 V
3. 8 V
4 2 V
5. 16 V
3. The energy stored by the inductor in question 2 above is calculated by2
2
LiW . What is
the energy stored in the magnetic field after 2 seconds?
1. 16 J
2. 8 J
3. 32 J
4. 4 J
5. 2 J
12
4. What is the current delivered by the source in the circuit shown in figure 1?
1. 30.125 A
2. 28.571 A
3 25.125 A
4 27.581 A
5. 30.561 A
5 What is the voltage drop in resistor R1 in the circuit in figure 1
1. 20V
2. 5V
3. 5.5V
4. 0.5V
5. none of the above
R12Ω
R2
1Ω
V110 V
R3
2Ω
R4
4Ω
R5
4ΩR6
2Ω
R7
3Ω
Figure 1
6. Refer to the voltage divider network shown in figure 2. What is the voltage between A and B?
1. 111.111 V
2. 90.000 V
3. 11.111 V
4. 100.000 V
5. 20.000 V
ECT1501/101/3/2018
13
100 V
1kΩ
5kΩ
4kΩ
A
B
Figure 2
7. The current Id in the circuit shown in figure 3 is equal to:
1. 12 A
2. 24 A
3. 4 A
4. -12 A
5. None of the above
Ia = 5 A Ib = 3 A
Ic = 4 A
Ix = 1 A
Id = ? A
Io = 7 A
Figure 3
8. Consider the circuit which contains the two sources as shown in figure 4. The current passing through the 3 ohm resistor in the circuit is:
1. 3.625 A
2. 4.625 A
3. 5.000 A
4. 6.635 A
5. 5.625 A
14
R1
5Ω
R2
10Ω
R3
3Ω
I15 A V1
20 V
Figure 4
9. From the circuit in figure 4, the power dissipated in the 3 ohm resistor when both the sources are acting simultaneously is given by:
1. 94.921 W
2. 96.990 W
3. 18.750 W
4. 29.290 W
5. 48.040 W
10. Consider the circuit in figure 5. What is the current passing through the 24 ohm resistance (when connected to the circuit)?
1. 0.330 A
2. 3.330 A
3. 33.330 A
4. 0.290 A
5. 0.400 A
R1
2Ω
R2
12Ω
V110 V
R3
24Ω
Figure 5
11. From the circuit in figure 5, what is the voltage drop across the 24 ohm resistance?
1. 8.570 V
2. 9.750 V
3. 6.125 V
ECT1501/101/3/2018
15
4. 5.875 V
5. 7.920 V
12. Norton’s equivalent form in any complex impedance circuit consists of?
1. an equivalent current source in parallel with an equivalent resistance.
2. an equivalent voltage source in series with an equivalent conductance.
3. an equivalent current source in parallel with an equivalent impedance.
4. both (1) and (2)
5. none of the above
13. In a pure capacitor, the voltage
1. is in phase with the current
2. is out of phase with the current
3. lags behind the current by 90°
4. leads the current by 90°
5. (3) and (4)
14. What is the total reactance of a series RLC circuit at resonance?
1. equal to XL
2. equal to XC
3. equal to R
4. zero
5. one
15. In a pure inductive circuit, voltage?
1. is in phase with the current
2. is out of phase with the current
3. lags behind the current by 90°
4. leads the current by 90°
5 (3) and (4)
16
16. The number of diodes used in a half-wave rectifier is
1. one
2. two
3. three
4. four
5 none of the above
17. The unit for measuring impedance is
1. Voltage
2. Ohms
3. Amplitude
4. Siemens
5 none of the above
18. Zener diodes are widely used as
1. current limiters
2, power distributors
3. voltage references
4. variable resistors
5 both (2) and (3)
19. The small variation in the output voltage of a DC power supply is called
1. average voltage
2. surge voltage
3. residual voltage
4. ripple voltage
5 rms voltage
20. For normal operation of an npn transistor, the base must be
1. disconnected
2. negative with respect to the emitter
ECT1501/101/3/2018
17
3. positive with respect to the emitter
4. positive with respect to the collector
5. neutral
TOTAL = 100%
18
ASSIGNMENT 2
QUESTION 1
1.1 Figure 1 shows colour-coded resistors, in 1.1.1 and 1.1.2 below. Determine the
resistance value and the tolerance of each.
1.1.1
(3)
1.1.2 (3)
Figure 1
1.2 If you need a 330Ω resistor and 5% tolerance, what colour bands would you look for?
(2)
[8]
QUESTION 2
2.1 Refer to the circuit in Figure 2 to determine
2.1.1 The total resistance between terminals A and B. (6)
2.1.2 The current, IT, IR2 and IR3 in each branch with 10 V between A and B. (6)
2.2 Using the currents found in, calculate voltage drop across:
2.2.1 R1 (2)
2.2.2.R2 (2)
2.2.3 R3 (2)
R1
100Ω
R2820Ω
R3
220Ω
R4820Ω
R5
100Ω
R6680Ω
R7
100Ω
R8
220Ω
R9
100Ω
A
B
I1=It I3 I5
I9=It
I2 I4
I8
Figure 2
[18]
silver green white orange
orange
orange brown gold
ECT1501/101/3/2018
19
QUESTION 3
3.1 The circuit in Figure 3 consists of resistances and a voltage source. Use Kirchoff’s Laws to determine the currents in the circuit. (8)
R5
5Ω
R4
2Ω
R3
4Ω
R1
3Ω
VT
12 V
R26Ω
ABC
D E F
I1I3
I2
Figure 3
3.2 Find the voltage between A and B in each voltage divider
3.2.1 of Figure 4 (2)
3.2.2 of Figure 5 (2)
100Ω
47Ω
V112 V A
B
2.2kΩ
3.3kΩ
V28 V
A
B
1kΩ
Figure 4 Figure 5
[12]
QUESTION 4
4.1 Convert the following angular values from radians to degrees:
4.1.1 2π/8 (1)
4.1.2 3π/5 (1)
20
4.2 The control dial settings of an analog oscilloscope shown in Figure 6 are set as follows:
The VOLTS/DIVISION switch is set at 0.35 mV. The TIME/DIVISION setting is set at
0.4 mS.
Figure 6
Determine:
4.2.1 the peak-to-peak voltage (2)
4.2.2 the period of the waveform on the screen. (2)
4.2.3 the frequency of the waveform. (2)
[8]
QUESTION 5
5.1 Capacitors are used for a variety of reasons in both AC and DC applications. Name
FIVE of the applications. (ANY FIVE) (5)
5.2 Refer to Figure 7 and calculate:
5.2.1 the total capacitance for the circuit (2)
5.2.2 the voltage across each capacitor (8)
Figure 7
[15]
ECT1501/101/3/2018
21
QUESTION 6
6.1 For the circuit in Figure 8, determine:
6.1.1 total circuit impedance (ZT) (6)
6.1.2 total circuit current (IT) (2)
6.1.3 voltage drops across C1, C2 and resistors R1 and R2 (8)
6.1.4 phase angle (θ) (2)
6.2 For the circuit in Figure 8, draw the phasor diagram showing all voltages and the total
current. (6)
R1
100Ω
R2
100Ω
C1
100nF
C2
220nF
V12 Vrms
15 Hz
0°
Figure 8
[24]
QUESTION 7
7.1 What would cause the barrier potential of a PN silicon diode to decrease from 0.7 V to 0.6 V? (2)
7.2 Determine whether each silicon diode in Figure 9 is forward- or reverse-biased with the corresponding depletion junction voltage drop. (8)
22
7.3 Determine the voltage across each diode in Figure 9. 5)
10Ω
56Ω
1kΩ
1.5kΩ
4.7kΩ
10kΩ 10kΩ
5 V 8 V
100 V
30 V
10 V 20 V 4.7kΩ
(a) (b)
(c) (d)
Figure 9
[15]
TOTAL = 100%
ECT1501/101/3/2018
23
ASSIGNMENT 3 QUESTION 1: PULSE RESPONSE OF REACTIVE CIRCUITS 1.1 Define the term ‘time constant’ as applied in RC circuits. (2) 1.2 Refer to Figure 1 below.
VT
50 V
S1
C1
0.01 uF
R1
8.2 k ohm
Figure 1 Calculate the following:
1.2.1 The time constant. (2) 1.2.2 The capacitor voltage 100 μs after the switch is closed if the capacitor is
initially uncharged. (2) 1.3 Sketch the charging curve of question 1.2 above. (2) [8]
[8] QUESTION 2: RL CIRCUITS 2.1 In the RC circuit in figure 2, determine the following:
2.1.1 The total resistance of the circuit (2) 2.1.2 The total inductance of the circuit (2) 2.1.3 The total Impedance and the phase angle in degree. (6)
R1
47ΩR2
10Ω
L1
50mH
L2
100mH
V15 Vrms
100 Hz
0°
Figure 2
[10]
QUESTION 3: SERIES RLC CIRCUITS AND RESONANCE
3.1 Analyze the circuit in Figure 3 and determine: 3.1.1 Total impedance (ZT) (6) 3.1.2 Total current (IT) (2)
3.2 State four conditions for a series RLC circuit to be at resonance. (4)
24
R1
220Ω
R2
390Ω
L1
500µH
L2
1mH
C110nF
C21.8nF
Vs
12 V
Figure 3
3.3 A certain series resonant circuit has a maximum current of 50mA and a VL of 100 V. The source voltage is 12 V. Find: 3.3.1 Total impedance (ZT) (2) 3.3.2 Inductive reactance (XL) (2) 3.3.3 Capacitive reactance (XC) (2)
[18]
QUESTION 4: TRANSFORMERS 4.1 Explain the operation of transformer. (4) 4.2 What does electrical isolation mean in transformers? (1) 4.3 Can a DC voltage be coupled by a transformer? (1) 4.4 For the circuit in Figure 4, find the turns ratio required to deliver maximum power to
the 4 ohm speaker. (2) 4.5 What is the maximum power in watts delivered to the speaker? (3)
R1
16Ω
4 ohm
25 V
1:2
Figure 4 [11]
QUESTION 5: PULSE RESPONSE OF REACTIVE CIRCUITS 5.1 A single 12 volts pulse with a width of 200 µS is applied to the integrator in Figure 5.
The source resistance is assumed to be zero. 5.1.1 To what voltage will the capacitor charge? (2) 5.1.2 How long will it take the capacitor to discharge? (3) 5.1.3 Show the output voltage waveform. (4)
ECT1501/101/3/2018
25
R1
10MΩC1nF
VoutVin
200 micro second
12 V
0 V
Figure 5
[9] QUESTION 6: INTRODUCTION TO SEMICONDUCTORS 6.1 Draw simple circuits to show:
6.1.1 Forward biased pn junction diode (2) 6.1.2 Reverse biased pn junction diode (2) (NB: Include limit resistors in your circuits)
6.2 Which bias condition produces majority carrier current? (1) 6.3 Which bias condition produces a widening of the depletion region? (1)
[6] QUESTION 7: DIODES AND APPLICATIONS
Determine the most likely failure on the circuit of Figure 6 for each of the following symptoms. State the correct action you would take in each case. The transformer has turns ratio of 5:1.
7.1 No voltage across primary. (1)
7.2 No voltage at point 2 with respect to ground; 110 V rms across the primary. (1)
7.3 No voltage at point 3 with respect ground; 110 V rms across the primary. (1)
7.4 150 V rms at point 2 with respect to ground; input is correct at 110 V rms. (1)
7.5 68 V at point 3 with respect to ground; input is correct at 110 V rms. (1)
C1
T1F1 BR1
1
2
4
3
SW1A
5:1 C2
IC1
LINE VREG
COMMON
VOLTAGE110 V
/ 60Hz
Vout
1
4
2
3
5
6
Figure 6
[5] TOTAL = 67%
26
SEMESTER 2
THE CUT-OFF SUBMISSION DATES FOR THE ASSIGNMENTS ARE :
Assignment 1: (Compulsory)
Assignment 2: (Compulsory)
Assignment 3: (Not compulsory)
29 August 2018
28 September 2018
ASSIGNMENT 1
TO BE COMPLETED ON MARK READING SHEET
Question 1
The SI unit for measuring an Inductor is
1) Volts 2) Inductance 3) Henry 4) Amperes 5) Both (1) and (4) Question 2
Which of the following is not an electrical quantity? 1) Time 2) Voltage 3) Current 4) Power 5) Resistance Question 3
The unit of measuring power is 1) Volt 2) Watt 3) Ampere 4) Joule 5) Ohm
Question 4
The primary purpose of a resistor is to 1) Increase pressure 2) Limit current 3) Produce heat 4) Resist current change 5) Increase current
ECT1501/101/3/2018
27
Question 5
The current in a given circuit is not to exceed 12 Amperes. Which value of fuse is best? 1) 10 A 2) 25 A 3) 20 A 4) A fuse is not necessary 5) All of the above Question 6
If you measure all the voltage drops and the source voltage in a series circuit and add them together, taking into consideration the polarities, you will get a result equal to 1) The source voltage 2) The total of the voltage drops 3) Zero 4) The total of the source voltage and the voltage drops 5) Both (1) and (2) Question 7
In Figure 1 what does each voltmeter indicate when the switch (J1) is in Position 1? 1) U1 = 0.0 V and U2 = 1.2 V 2) U1 = 0.0 V and U2 = 12 V 3) U1 = 12 V and U2 = 0.0 V 4) U1 = U2 = 24 V 5) None of the above Question 8
In Figure 1 what does each voltmeter indicate when the switch (J1) is in position 2? 1) U1 = 1.2 V and U2 = 12 V 2) U1 = 0.0 V and U2 = 12 V 3) U1 = 12 V and U2 = 0.000 V 4) U1 = U2 =24 V 5) None of the above
R1 R2
J1
V1
12 V U10.000 V
+
-
U20.000 V
+
-
1
2
Figure 1
28
Question 9
For 10 V and 50 mA, the power is 1) 500 mW 2) 0.5 W
3) 500 000 W 4) Answers (1), (2), and (3) 5) None of the above Question 10
When you connect an ammeter in a series resistive circuit and turn on the source voltage, the meter reads zero. You should check for 1) A broken wire 2) A shorted resistor 3) An open resistor 4) Both (1) and (3) 5) Short circuit Question 11
When a 1.2 kΩ resistor and a 100 Ω resistor are connected in parallel, the total resistance is 1) Greater than 1.2 kΩ 2) Greater than 100 Ω but less than 1.2 kΩ 3) Less than 100 Ω but greater than 90 Ω 4) Less than 90 Ω 5) Greater than 99 Ω Question 12
If 120 mA of current is supplied into a parallel circuit consisting of three branches and two of the branch currents are 40 mA and 20mA respectively, then the third branch current is 1) 30 mA 2) 20 mA 3) 160 mA 4) 40 mA 5) 60 mA Question 13
The output of a certain voltage divider is 9 V with no load. When a load is connected, the output voltage 1) Increases 2) Decreases 3) Remains the same 4) Becomes zero 5) Both (1) and (2)
ECT1501/101/3/2018
29
Question 14
How many amperes of current flows when 8 coulombs of charge flow past a given point in a wire in 0.2 seconds? 1) 2.5 A 2) 10 A 3) 40 A 4) 20 A 5) 50 A Question 15
An uncharged capacitor and a resistor are connected in series with a switch and a 12 V battery. At the instant the switch is closed, the voltage across the capacitor is 1) 12 V 2) 6 V 3) 24 V 4) 0 V 5) 3 V Question 16
A magnetic field is made up of 1) Positive and negative charges 2) Magnetic domains 3) Flux lines 4) Magnetic poles 5) Electric field Question 17
Calculate the total resistance of two 180Ω resistor that are connected in parallel. 1) 360Ω 2) 180Ω 3) 99Ω 4) 100Ω 5) 90Ω Question 18
Four 10 mH inductors are in series. The total inductance is 1) 40 mH 2) 2.5 mH 3) 40 000 μH 4) 25 mH 5) Answers (1) and (3)
30
Question 19
Figure 2 shows three capacitors that are connected in series. The total capacitance of the circuit is 1) 6.69 pF 2) 0.69 F 3) 0.069 pF 4) 69.69 pF 5) 69.69 nF
C1
100pF
C2
560pF
C3
390pF100 V
Figure 2 Question 20
Refer to Figure 2. The total charge stored by the series capacitors is 1) 6.69 pC 2) 0.69 C 3) 0.069 pC 4) 69.69 pC 5) 6.969 nC
Total marks = 100%
ECT1501/101/3/2018
31
ASSIGNMENT 2
QUESTION 1
1.1 Define Ohm’s Law. (2)
1.2 Study the circuit shown in Figure 1. Calculate the currents for the voltage values of 0, 50, 100, 150 and 200. (10)
1.3 Sketch the current (in mA) versus voltage (in Volts) graph. (3)
R1
1.0kΩVo
current, I
Figure 1
[15]
QUESTION 2
2.1 State:
2.1.1 Superposition Theorem. (2)
2.1.2 Kirchoff’s Voltage Law. (2)
2.2 Consider the circuit, which contains the two sources as shown in figure 2. Use the Superposition Theorem to determine:
2.2.1 The current passing through the 3Ω resistor in the circuit is: (5)
2.2.2 The power dissipated in the 3Ω resistor when both sources are active simultaneously (6)
R1
5Ω
R2
10Ω
R3
3Ω
I15 A V1
20 V
Figure 2
[15]
32
QUESTION 3
For the circuit in figure 3,
Calculate:
3.1 IS (7)
3.2 VR (2)
3.3 VC (2)
3.4 VC (2)
(use complex notation)
3.5 Sketch the voltage phasor diagram (6)
3.6 Verify KVL around the closed path (2)
R1
6Ω
R2
4Ω
L1
50mH
L2
50mHC1200µF
C2200µF
E
20V
Figure 3
[21]
QUESTION 4
4.1 Define the following terms:
4.1.1 Frequency (1)
4.1.2 Period (1)
ECT1501/101/3/2018
33
4.2 For the sine wave in figure 4 determine:
4.2.1 The peak value (2)
4.2.2 The peak-to-peak value (2)
4.2.3 The rms value (2)
4.2.4 The average value (2)
4.2.5 The frequency (3)
Figure 4
[13]
QUESTION 5
5.1 Explain the operation of a transformer. (4)
5.2 To step 100 volts down to 50 volts, what must be the turn’s ratio of the transformer? (2)
[6]
QUESTION 6
6.1 Describe the process of doping to form semiconductor materials. (2)
6.2 Explain why a series resistor is necessary when a pn junction is forward biased.
(2)
6.3 Draw the curves to show only the forward characteristics of both Germanium and
Silicon diodes. (4)
[8]
V (volts)
T (mS)
-25
25
0 1 2
34
QUESTION 7
7.1 Draw a neat circuit diagram of a full-wave rectifier that uses a center-tapped transformer. (4)
7.2 Sketch the voltage waveform across load resistor if a capacitor is included in the circuit you have drawn in question 7.1 above. (2)
7.3 Calculate the peak voltage rating of each half of a center-tapped transformer used in a full-wave rectifier that has an average output voltage of 110 V. (4)
[10]
QUESTION 8
8.1 A transformer with a step-down ratio of 20:1, supplied with mains voltage of 220 Vrms at 50 Hz is connected to a bridge rectifier circuit using four silicon diodes with a 100 Ω load resistor (RL).
8.1.1 Sketch the input sinusoidal waveform. (2)
8.1.2 Sketch the waveform you would expect to find across RL. (2)
8.1.3 Calculate:
(a).The Root-Mean-Square (RMS) value of voltage across RL. (3)
(b) The average value of voltage across RL. (3)
(c) The required Peak Inverse Voltage (PIV) rating of the diode. (2)
[12]
TOTAL MARK = 100%
ECT1501/101/3/2018
35
ASSIGNMENT 3
(SELF EVALUATION DO NOT SUBMIT)
QUESTION 1: VOLTAGE, CURRENT, AND RESISTANCE 1.1 Determine the resistance values represented by the alphanumeric labels in the parts
shown below: 1.1.1 4k4 (1) 1.1.2 0.01k (1) 1.1.3 9M (1) 1.1.4 47R (1)
1.2 Colour coding is used to specify the resistance values (in ohms) as well as tolerance and
reliability. For five colour band resistors, what does the following represent? 1.2.1 First three bands. (1) 1.2.2 Fourth colour band. (1) 1.2.3 Fifth colour band. (1)
1.3 A 12 V source is connected across a 10 Ω resistor for 2 minutes. 1.3.1 What is the power dissipation in the 10Ω resistor? (3) 1.3.2 How much energy is used? (3) 1.3.3 If the resistor remains connected for an additional minute, does the power
dissipation increases or decreases, and why? (2) [15]
QUESTION 2: OHM’S LAW, ENERGY AND POWER 2.1 Define Ohm’s Law. (2) 2.2 Study the circuit shown in Figure 1. Calculate the currents for the voltage values of 0, 50,
100, 150 and 200. (10) 2.3 Sketch the current (in mA) versus voltage (in Volts) graph. (3)
R1
1.0kΩVo
current, I
Figure 1 [15]
QUESTION 3: KIRCHOFF’S VOLTAGE LAW 3.1 For the circuit shown in Figure 2, determine the unknown voltage drop V1. (3)
20 V
2 V 1 V
V1
5 V
8 V
Figure 2
36
3.2 Refer to Figure 3. Use the voltage divider rule to calculate
3.2.1 Voltage drop across terminal A and B. (3) 3.2.2 Voltage drop across terminal B and C. (3)
12 V
22Ω
47Ω
A
B
C
Figure 3 3.3 Determine the total voltage across points A and C. (3)
[12] QUESTION 4: INTRODUCTION TO ALTERNATING CURRENT AND VOLTAGE 4.1 Define period of a waveform. (2) 4.2 Refer to the sine wave displayed on the scope screen in Figure 4. The horizontal axis is
0 V. Determine 4.2.1 The peak value. (3) 4.2.2 The root-mean-square. (3) 4.2.3 The period. (3) 4.2.4 The frequency. (2)
[13]
Ch 1 V/DIV: 0.2 V T/DIV: 50 ms
Figure 4
QUESTION 5: RC CIRCUITS 5.1 Define the term ‘time constant’ as applied in RC circuits. (2) 5.2 A series RC circuit has a 270 kΩ resistor and a 2200 pF capacitor. What is the time
constant in S ? (3)
ECT1501/101/3/2018
37
5.3 How long does it take C1 of 1.5 microfarad to discharge to 3 V in Figure 5? The
capacitor has initial condition (IC) of 25 V. (Hint: t
-RC
iv = Ve ). (5)
C1IC=25V
SW1
R11kΩ
Figure 5
[10] QUESTION 6: RLC CIRCUITS 6.1 What is resonance? (2) 6.2 The total impedance of the series RLC circuit is given by
T
1Z ω =R+ j ωL -
ωC. (4)
6.2.1 Prove that, at resonance, 1
f =r2π LC
.
6.2.2 If R = 10 Ω and 1
ωL =ωC
, what is the value of TZ ? (1)
6.3 Calculate the resonance frequency of the series RLC circuit of Figure 6. (3)
R1
22Ω
L1
20mH
C1
47µF Figure 6
[10] QUESTION 7: SEMICONDUCTORS AND PN JUNCTION DIODES 7.1 Explain the following terms:
7.1.1 Doping. (2) 7.1.2 Forward bias. (2)
7.2 A germanium diode is connected as shown in Figures 7a and 7b. What is the approximate voltage drop across each diode in each circuit? (2)
7.2.1 7.2.2
38
R
Vbias
R
Vbias
V
0.000 V
+-
0.000 V
+-
V
D D
Figure 7a Figure 7b 7.3 Sketch the resulting output waveforms for the input signal at each diode: 7.3.1 (2)
IN OUTD
7.3.2 (2)
IN OUTD
[10] QUESTION 8: DIODES AND APPLICATIONS 8.1 Sketch the characteristic curve to show the pn junction silicon diode in the forward and
reverse regions. (8) 8.2 Study the following list of components:
220 V / 12 V, 2 A transformer 220 V / 12 -0-12 V, 2 A transformer 3 × 1N4004 diodes 2 × Electrolytic capacitors
Choose the correct components and sketch the following circuit diagrams. 8.2.1 A half wave rectifier. (3) 8.2.2 A full wave rectifier. (4) Clearly label the components on each circuit diagram.
[15]
TOTAL MARK = 100%
ECT1501/101/3/2018
39
8.7 Other assessment methods
None
8.8 The examination
Use your my Studies @ Unisa brochure for general examination guidelines and examination preparation guidelines.
9 FREQUENTLY ASKED QUESTIONS
The my Studies @ Unisa brochure contains an A-Z guide of the most relevant study information.
10 SOURCES CONSULTED
None
11 CONCLUSION
Please ensure that you have all the tutorial letters and prescribed book available before starting with your studies.
Tutorial letter 201, with the memoranda of the assignments wil
12 ADDENDUM
None