Basic Electronics 500 - Lecture notes 2 PDF

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FACULTY OF MEDIA, INFORMATION & COMMUNICATIONS TECHNOLOGY HIGHER CERTIFICATE IN SYSTEMS ENGINEERING

BASIC ELECTRONICS 500 YEAR 1

SEMESTER 1

Registered with the Department of Higher Education as a Private Higher Education Institution under the Higher Education Act, 1997. Registration Certificate No. 2000/HE07/008

FACULTY OF MEDIA INFORMATION AND COMMUNICATION TECHNOLOGY QUALIFICATION TITLE HIGHER CERTIFICATE IN SYSTEMS ENGINEERING

LEARNER GUIDE MODULE: BASIC ELECTRONICS 500 (1ST SEMESTER)

PREPARED ON BEHALF OF

5*, (PTY) LTD AUTHOR: Mr Katlego Luther Mahlako Malesa EDITOR: Mr Caston Zimunhu FACULTY HEAD: Mr Isaka Reddy Copyright © 2019 Registration Number: 2000/000757/07 All rights reserved; no part of this publication may be reproduced in any form or by any means, including photocopying machines, without the written permission of the Institution.

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LESSON PLAN ALIGNED TO MOBILE CONTENT [MOODLE]

SECTION

SUBJECT MATTER

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BSc. IN INFORMATION TECHNOLOGY

INTRODUCTION

1.1

Scientific Notation

1.2

Metric Prefixes

1.3

System of Units

Lesson 2

1.4

Charge

Lesson 3

1.5

Basic Electrical Circuit

Lesson 4

1.6

Relationship between Current, Voltage and Resistance

1.7

Open, Closed and Short Circuits

Lesson 1

2

Lesson 5

DIRECT CURRENT

2.1

Direct Current

Lesson 6

2.2

Alternating Current

Lesson 7

2.2.1

Properties of AC

Lesson 8

2.3

Applications of AC

Lesson 9

3

RESISTORS

3.1

Types of resistors

Lesson 10

3.2

Color Coding

Lesson 11

3.3

Variable resistors

3.4

Power Rating of Resistors

3.5

Resistor Troubles

Lesson 11

3.6

Checking Resistance

Lesson 12

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Lesson 10

ELECTRICAL CIRCUITS

4.1

Series Circuit

Lesson 13

4.2

Drop Series Circuit

Lesson 14

4.3

Total Power in a Series Circuit

Lesson 15

4.4

Parallel Circuit

Lesson 16

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4.5

Kirchhoff’s Laws

Lesson 17

4.6

RL, RC and RLC Circuits

Lesson 18

INTERACTIVE ICONS USED IN THIS LEARNER GUIDE

Learning Outcomes Study

Think Point

Research

Review Questions

Case Study

Read

Glossary

Bright Idea

Writing Activity

Key Point

Problem(s)

4

Web

References

Resource Multimedia Resource

Worked Example

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TOPIC ONE | ELETRIC CHARGE

LEARNING OUTCOMES

1. Demonstrate a sound understanding of electrical components and electronic circuits. 2. Demonstrate an understanding of the relationship between Current, Voltage And Resistance.

Introduction Electric circuit theory and electromagnetic theory are the two fundamental theories upon which all branches of electrical engineering are built. Many of electrical engineering such as power, electric machines, control, electronics, communication and instrumentation are based on electric circuit’s theory. Therefore, there basic electric circuits theory course is the most important course for an electrical engineering student and always an excellent starting point for a beginning student. Electrical engineering circuit’s theory is also valuable to students specializing in branches of the physical sciences because circuits are a good model for the study of energy systems. In general and because of the applied mathematics, physics and topology involved in electrical engineering, we are often interested in communicating or transferring energy from one point to another .To do this requires an interconnection of electrical devices such interconnection is referred to as an electric circuit and each component of the circuit is known as an element. An electrical circuit is an interconnection of electrical elements 1.1 Scientific Notation Before jumping directly into scientific notation, let’s take a closer look at powers of 10. A power of 10 is an exponent of the base 10 and can be either positive or negative.

Positive powers of 10 are used to indicate numbers greater than 1, whereas negative powers of 10 are used to indicate numbers less than 1. Table 1–1 shows the powers of 10 ranging from 10−12to 109 and their equivalent decimal

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values. In electronics, you will seldom work with powers of 10 outside this range. Expressing a Number in Scientific Notation The procedure for using any form of powers of 10 notation is to write the original number as two separate factors. Scientific notation is a form of powers of 10 notation in which a number is expressed as a number between 1 and 10 times a power of 10. The power of 10 is used to place the decimal poi nt correctly. The power of 10 THINK POINT indicates the number of places by which the What is the value of decimal point has been moved to the left or any number raised to right in the original number. If the decimal the power of 0? point is moved to the left in the original number, then the power of 10 will increase or become more positive. Conversely, if the decimal point is moved to the right in the original number then the power of 10 will decrease or become more negative. Let’s take a look at an example.

Table 1.1: Scientific Notation

1.2 Metric Prefixes The metric prefixes represent those powers of 10 that are multiples of 3. In the field of electronics, engineering notation is much more common than scientific notation because most values of voltage, current, resistance, power, etc. are specified in terms of the metric prefixes. Once a number is e xpressed in engineering notation, its power of 10 can be replaced directly with its corresponding metric prefix. Table 1 –2 lists the most common metric prefixes and their corresponding powers of 10. Notice that uppercase letters are used 7

for the abbreviations of the prefixes involving positive powers of 10, whereas lowercase letters are used for negative powers of 10. There is one exception to the rule however; the lowercase letter “k” is used for kilo corresponding to 𝟏𝟎𝟑. Notice that 33,000 Ω or 33 x 103 Ω can be expressed as 33 kΩ.

Table 1-2: Metric Prefixes

1.3 Systems of Units Table I–3 lists many of the electrical quantities that you will encounter in your study of electronics. For each electrical quantity listed in Table I–3, take special note of the unit and symbol shown. In the examples and problems that follow, we will use several numerical values with the various symbols and units from this table.

Table 1-3: SI Units

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1.4 Charge The concept of electric charge is the underlying principle for explaining all electrical phenomena. Also, the most basic quantity in an electric circuit is the electric charge. We all experience the effect of electric charge when we try to remove our wool sweater and have and have it stick to our body or walk across a carpet and receive a shock A charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C). The charge e on an electron is negative and equal in magnitude to 1.602 x 1019 C, while a proton carries a positive charge of the same magnitude as the electron. The presence of equal numbers of protons and electrons leaves an atom neutrally charged. The following points should be noted about electric charge: 



The coulomb is a large unit for charges. In 1C of charge, there are 1/(1.602x10-19) = 6.24x1018 electrons. Thus realistic or laboratory values of charges are on the order of pC , nC or µC.



According to experimental observations, the only charges that occur in nature are integral multiples of the electronic charge e = 1.602x10-19 C.



The Law of conservation of charges states that charges can neither be created nor destroyed only transferred. Thus the algebraic sum of electric charges in a system does not change. We can now consider the flow of electric charges. A unique feature of electric charge or electricity is the fact that it is mobile, that is, it can be transferred from one place to another, where it can be converted to another form of energy.



When conducting wire (consisting of several atoms) is connected to a battery (a source of electromotive force), the charges are compelled to move, positive charges move in the direction. While negative charges move in the opposite direction. It is conventional to take the current flow as the movement of positive charges.

Problems 1.1 Express each of the following numbers in scientific notation: i. 29 000 ii. 0,000075 iii. 789 iv. 0,00298 For more practice go to page 18 of the prescribed book: http://www.amazon.com/Grobs-Basic-Electronics-MitchelSchultz/dp/0073510858

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1.5 The Basic Electrical Circuit Understanding the electrophysiology of the voltage involves a basic understanding of electrical circuits. By basic, I mean really simple, so don't get scared yet. Figure 1.1 below shows a typical simple circuit.

Figure 1.1: Electrical Circuit

Voltage It is the force created by the separation of charges. Kind of like when two opposite poles of a magnet are put close together, but are separated by a short distance. A force tries to pull them together. When there are more negative charges on the inside of the membrane of a cell, there is a force driving positive charges inward to neutralize them. The unit of voltage is the volt and it is represented by the symbol V. Voltage is also called "potential" or "potential difference". Resistance It is a measure of how hard it is for charges to move in the system. In a cell, the lipid portion of the membrane is impermeable to ions, so the resistance to current across the membrane is determined by the opening and closing of ion channels. When the channels open, the resistance decreases. When they close, resistance increases (because ions can't move through the membrane). The units of resistance are ohms and it is represented by the symbol R. (Note When talking about channels, "conductance" is usually used instead of resistance. Conductance is the inverse of resistance (1/R), or how easy it is to pass charges. Its units are Siemens (S). Current It is the movement of charges. In an electrical circuit, electrons move from the negative pole to the positive pole (although electrical current is defined as the movement of positive charges, so current is said to go from the positive pole to negative pole - go figure). In cells, current is when ions move through the membrane (usually Na+, K+, Ca2+, or Cl-). 10

1.5.1 Current Measuring Devices Figure 1.2 shows a meter measuring the current in a simple dc circuit consisting of a battery and a resistor. Notice that the meter is connected between the positive terminal of the battery and the right lead of the resistor. Unlike voltage measurements, current measurements must be made by placing the meter in the path of the moving charges. To do this, the circuit must be broken open at some point, and then the leads of the meter must be connected across the open points to recomplete the circuit. When measuring the current in a dc circuit, the black lead of the meter should be connected to the point that traces directly back to the negative side of the potential difference. Likewise, the red lead of the meter should be connected to the point that traces directly back to the positive side of the potential difference. When measuring ac currents, the orientation of the meter leads is unimportant.

Figure 1.2: Measuring

Current

Current clamp In electrical and electronic engineering, a current clamp or current probe is an electrical device having two jaws which open to allow clamping around an electrical conductor. This allows properties of the electric current in the conductor to be measured, without having to make physical contact with it, or to disconnect it for insertion through the probe. Current clamps are usually used to read the magnitude of a sinusoidal current (as invariably used in What are the different alternating current (AC) power distribution types of current clamps? systems), but in conjunction with more List the other current advanced instrumentation the phase and measuring devices that you waveform are available. know.

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If R increases, V has to increase to keep their quotient (I) constant. What would happen to the pressure if you decrease the flow (by turning down the faucet) while keeping the nozzle on the hose (constant resistance)? If the resistance is kept constant and the flow is reduced by closing the faucet, the water pressure decreases: If I decrease, V has to decrease to keep their How does the graph that quotient (R) constant. This basic concept depicts the relation (keeping one variable constant, changing between I, V and R look another, resulting in the third changing) will like? Sketch it labelling both axis. help you to understand the voltage clamp.

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1.7 Open, Closed and Short Circuits A complete path through which electricity flows. As the term implies, circuits tend to be circular in design, but the starting point for electricity is not the same as the end point. It only appears so with most circuits because the start point and end point are usually located close together. A circuit can be created between any two points if there is available electricity at one of the points and a clear path for it to travel to the opposite point. Electricity will only flow continuously if a circuit exists, and it must be a complete circuit. 1.7.1 Open Circuit, Closed circuit Any circuit which is not complete is considered an open circuit. A complete circuit which is not performing any actual work can still be a closed circuit. For example, a circuit connected to a dead battery may not perform any work, but it is still a closed circuit. A circuit is considered to be closed when electricity flows from an energy source to the desired endpoint of the circuit. The open status of the circuit doesn't depend on how it became unclosed, so circuits which are manually disconnected and circuits which have blown fuses, faulty wiring or missing components are all considered open circuits. 1.7.2 Short Circuit A condition in any circuit of ant size in which power jumps from the energy source to either a ground point or to the end of the circuit without actually completing the full circuit. Since this condition shortens the route travelled by the electricity, the condition is known as a short circuit. Short circuits in energy transmission systems usually result in an overload which can result in anything from a harmless blown fuse to a lethal electrical fire. Most common short circuits that occur in household electrical service are potentially hazardous which is why fuses and breakers are so critical to safe electrical service. But a short doesn't necessarily indicate a hazard condition. For example, if a coin is accidentally set against the two poles of a 9-volt smoke-alarm-type battery, this creates a short circuit which rapidly drains the battery, but the condition is not a hazardous one because of the low voltage and storage capacity of these small energy sources.

Figure 1.4: Short circuit

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TOPIC TWO | ALTERNATING AND DIRECT CURRENT

LEARNING OUTCOMES

1. Demonstrate a sound understanding of alternating voltage and current. 2. Demonstrate an understanding of the characteristics alternating current and its applications.

2.1 Direct Current Direct Current (DC) is the unidirectional flow or movement of electric charge carriers (which are usually electrons). The intensity of the current can vary with time, but the general direction of movement stays the same at all times. As an adjective, the term DC is used in reference to voltage whose polarity never reverses. In a DC circuit, electrons emerge from the negative, or minus, pole and move towards the positive, or plus, pole. Nevertheless, physicists define DC as travelling from plus to minus. Direct current is produced by electrochemical and photovoltaic cells and batteries. Virtually all electronic and computer hardware needs DC to function. Most solid-state equipment requires between 1.5 and 13.5 volts. Current demands can range from practically zero for an electronic wristwatch to more than 100 amperes for a radio communications power amplifier. Equipment using vacuum tubes, such as a high-power radio or television broadcast transmitter or a CRT (cathoderay tube) display, require from about 150 volts to several thousand volts DC.

Figure 2.1: Direct Current

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2.2 Alternating Current In alternating current ( AC ) the movement of electric charge periodically reverses direction. In direct curren (DC), the flow of electric charge is only in one direction. AC is the form in which electric power is delivered to businesses and residences. The usual wavefor of an AC powe r circuit is a sine wave In certain applications, different waveforms are used, such astriangular or square waves. Audi and radi signals carried on electrical wires are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal. When a sine wave of alternating voltage is connected across a load resistance, the current that flows in the circuit is also a sine wave.

Figure 2. 2: A sine wave of alternating voltage applied across R produces a sine wave of alternating current in the circuit.

Alternating Current vs. Direct Current The figure below shows the schematic diagram of a very basic DC circuit. It consists of nothing more than a source (a producer of electrical energy) and a load (whatever is to be powered by that electrical energy). The source can be any electri cal source: a chemical battery, an electronic power supply, a mechanical generator, or any other possible continuous source of electrical energy. For simplicity, we represent the source in this figure as a battery.

Figure 2 .3 : DC Circuit

At the same time, the load c an be any electrical load: a light bulb, electronic clock or watch, electronic instrument, or anything else that must be driven by a continuous source of electricity. The figure here represents the load as a simple resistor. 17

Regardless of the specific source and load in this circuit, electrons leave the negative terminal of the source, travel through the circuit in the direction shown by the arrows, and eventually return to the positive terminal of the source. This action continues for as long as a complete electrical circuit exists.

Figure 2.4: Alternating Current versus Direct Current

Now consider the same circuit with a single change, as shown in the second Figure 2.4 above. This time, the energy source is constantly changing. It begins by building up a voltage which is positive on top and negative on the bottom, and therefore pushes electrons through the circuit in the direction shown by the solid arrows. However, then the source voltage starts to fall off, and eventually reverse polarity. Now current...