CASA B-03a Electrical Fundamentals I PDF

MODULE 03 Category B Licence CASA B-03a Electrical Fundamentals I  Copyright © 2024 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, w...

MODULE 03 Category B Licence CASA B-03a Electrical Fundamentals I  Copyright © 2024 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, without the written permission of Aviation Australia. CONTROLLED DOCUMENT 2024-01-23 B-03a Electrical Fundamentals Page 2 of 302 CASA Part 66 - Training Materials Only  Knowledge Levels Category A, B1, B2 and C Aircraft Maintenance Licence Basic knowledge for categories A, B1 and B2 are indicated by the allocation of knowledge levels indicators (1, 2 or 3) against each applicable subject. Category C applicants must meet either the category B1 or the category B2 basic knowledge levels. The knowledge level indicators are defined as follows: LEVEL 1 Objectives: The applicant should be familiar with the basic elements of the subject. The applicant should be able to give a simple description of the whole subject, using common words and examples. The applicant should be able to use typical terms. LEVEL 2 A general knowledge of the theoretical and practical aspects of the subject. An ability to apply that knowledge. Objectives: The applicant should be able to understand the theoretical fundamentals of the subject. The applicant should be able to give a general description of the subject using, as appropriate, typical examples. The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject. The applicant should be able to read and understand sketches, drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using detailed procedures. LEVEL 3 A detailed knowledge of the theoretical and practical aspects of the subject. A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner. Objectives: The applicant should know the theory of the subject and interrelationships with other subjects. The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples. The applicant should understand and be able to use mathematical formulae related to the subject. The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using manufacturer's instructions. The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. 2024-01-23 B-03a Electrical Fundamentals Page 3 of 302 CASA Part 66 - Training Materials Only  Table of Contents Electron Theory (3.1) 12 Learning Objectives 12 Electron Theory 13 Atoms 13 Electron Shells 14 Energy Levels 15 Electron Flow 16 Energy Bands 18 Ions 19 Molecules 20 Compounds 21 Electrical Properties of Molecules and Compounds 22 Conductors, Insulators and Semiconductors 25 Conductors 25 Insulators 26 Semiconductors 26 Static Electricity and Conduction (3.2) 29 Learning Objectives 29 Static Electricity 30 Static Charge 30 Triboelectric Effect 30 Coulomb’s Law of Charges 33 Distribution of Electrostatic Charges 34 Electrostatic Attraction and Repulsion 34 Dissipation of Accumulated Charges 35 Conduction of Electricity in Materials 37 Conduction of Electricity in Solids 37 Relative Resistances of Solid Conducting Materials 38 Conduction of Electricity in Liquids 39 Conductivity of Liquids 40 Conduction of Electricity in Gases 42 Thermionic Emission 43 Conduction of Electricity in a Vacuum 45 Electrical Terminology (3.3) 47 2024-01-23 B-03a Electrical Fundamentals Page 4 of 302 CASA Part 66 - Training Materials Only  Learning Objectives 47 Electrical Terminology 48 Electric Charge 48 Electric Current 48 Electric Current Flow Conventions 49 Electromotive Force/Voltage 50 Potential Difference 50 Resistance 52 Ohm's Law 53 Conductance 53 Generation of Electricity (3.4) 55 Learning Objectives 55 Generation of Electricity 56 Voltage Produced by Friction 56 Voltage Produced by Pressure 58 Voltage Produced by Heat 60 Voltage Produced by Light 61 Voltage Produced by Chemical Action 63 Voltage Produced by Magnetism and Motion 65 DC Sources of Electricity I (3.5) 70 Learning Objectives 70 The Cell 71 Galvanic Cell 71 Container 71 Electrodes 72 Electrolyte 73 Electrochemical Action 74 Cell Categories 75 Primary Cells 76 Alkaline Cells 77 Secondary Cells 78 Lead-Acid Battery Construction 80 Lead-Acid Battery 80 Battery Construction 80 Lead-Acid Electrolyte 82 Electrochemical Reaction 83 2024-01-23 B-03a Electrical Fundamentals Page 5 of 302 CASA Part 66 - Training Materials Only  Lead-Acid Discharging 84 Lead-Acid Charging 85 Service Life Killers 86 Internal Resistance of Electric Cells 87 Nickel-Cadmium Cell 89 Introduction to the Nickel-Cadmium Cell 89 Nickel-Cadmium Cell Thermal Runaway 90 Neutralising Spills 92 Other Types of Secondary Cells 94 Modern Cells 94 Silver-Zinc Cells 94 DC Sources of Electricity II (3.5) 96 Learning Objectives 96 Combining Cells 97 Connecting Cells 97 Battery Voltage 97 Series Connected Cells 98 Series Cell Implementation 99 Parallel Connected Cells 99 Series-Parallel Connected Cells 102 Thermocouples 106 Purpose of Thermocouples 106 Thermocouple Operation 106 Typical Thermocouples 108 Light 110 Electromagnetic Radiation 110 Photoelectric Cell 110 Anatomy of a Solar Cell 112 DC Circuits (3.6) 115 Learning Objectives 115 Voltage, Current and Resistance 116 Ohm's Law 116 Kirchhoff's Current Law 117 Kirchhoff's Voltage Law 117 Circuit Analysis 119 Series Aiding and Opposing EMF Sources 124 Current Dividers 124 2024-01-23 B-03a Electrical Fundamentals Page 6 of 302 CASA Part 66 - Training Materials Only  Voltage Dividers 127 DC Power Supply Internal Resistance 128 Resistance and Resistor I (3.7) 130 Learning Objectives 130 Resistance 131 Resistance 131 Factors Affecting Resistance 131 Specific Resistance/Resistivity 134 Resistor Stability vs Temperature 135 Resistor Labelling 136 Resistor Colour Codes 136 Four-Band Resistor Colour Code 136 Five-Band Resistor Colour Code 137 Resistor Markings 138 Standard EIA Decade Resistor Values Table 139 Wattage Ratings 141 Resistors Connected in Series and Parallel 142 Resistors Connected in Series 142 Resistors Connected in Parallel 142 Series-Parallel Combinations 143 Complex Series-Parallel Combinations 145 Resistance and Resistor II (3.7) 149 Learning Objectives 149 Potentiometers and Rheostats 150 Potentiometer 150 Rheostat 150 Galvanometer 151 Wheatstone Bridges 153 Purpose of the Wheatstone Bridge 153 Wheatstone Bridge Operation 153 Temperature Coefficient 156 Conductance 156 Temperature Effect on Resistance 156 Fixed Resistors 159 Resistors 159 Thermistors and Voltage Dependent Resistors 163 Thermistors 163 2024-01-23 B-03a Electrical Fundamentals Page 7 of 302 CASA Part 66 - Training Materials Only  Voltage-Dependent Resistor 165 Power (3.8) 167 Learning Objectives 167 Power, Work and Energy 168 Work 168 Energy 168 Kinetic Energy and Potential Energy 169 Work and Power 170 Power 171 Electrical Formulae 173 Power Calculations 174 Capacitance and Capacitors (3.9) 177 Learning Objectives 177 Basic Capacitor 178 Capacitor and Capacitance 178 Capacitor Operation 178 Factors Affecting Capacitance 181 Capacitance Values 181 Physical Properties 181 Area of Plates and Number of Plates 182 Distance Between Plates 182 Dielectric 183 Dielectric Constant 184 Dielectric Strength 184 Working Voltage 185 Construction and Identification of Capacitors 187 Common Capacitors 187 Ceramic Capacitors 187 Mica Capacitors 188 Electrolytic Capacitors 189 Tantalum Capacitors 189 Capacitor Identification 190 Variable Capacitors 191 Charging and Discharging of Capacitors 193 Capacitance and Charge 193 Resistor Capacitor Circuits 194 Exponential Capacitor Charge 195 2024-01-23 B-03a Electrical Fundamentals Page 8 of 302 CASA Part 66 - Training Materials Only  Time Constant for Exponential Charge 196 Exponential Capacitor Discharge 196 Calculating Circuit Capacitance 198 Capacitors Connected in Parallel 198 Capacitors Connected in Series 198 Testing Capacitors 201 Visual Inspection 201 Verify the Correct Capacitance 201 Magnetism I (3.10) 204 Learning Objectives 204 Magnetism 205 Magnetism and Electricity 205 Weber’s Theory of Magnetism 205 Domain Theory 207 Magnetic Flux and Flux Density 208 Magnetic Materials 210 Magnetic Poles 214 Earth's Magnetic Poles 214 Law of Magnetic Poles 215 Magnetic Lines of Force 216 General Properties of Magnetic Lines of Force 217 Magnetisation 219 Demagnetisation 221 Magnetic Shielding 223 Magnetic Properties and Materials 226 Reluctance and Permeability 226 Saturation Point 226 Hysteresis 227 Coercivity and Remanence in Permanent Magnets 229 Magnetism II (3.10) 232 Learning Objectives 232 Electromagnetic Fields 233 Electromagnets 233 Left-Hand Grasp Rule 233 Parallel Conductors 235 Electromagnetic Fields 235 Effect of Multiple Coils 236 2024-01-23 B-03a Electrical Fundamentals Page 9 of 302 CASA Part 66 - Training Materials Only  Left-Hand Grasp Rule for Polarity 237 Electromagnetic Field Strength 238 Magnetomotive Force 241 Magnetic Field Strength 241 Field Intensity/Field Strength 242 Magnetic Flux Density 243 Eddy Currents 244 Care of Magnets 245 Magnetic Terminology 246 DC Motor and Generator Theory (3.12) 248 Learning Objectives 248 DC Generator Theory 249 Electromagnetic Induction 249 Left-Hand Rule for Generators 250 Basic AC Generator 251 Generator Principles 256 Elementary DC Generator 257 Typical DC Generator Construction 258 Generator Field Frame 260 Effect of an Additional Armature Coil 261 Electromagnetic Poles 263 Brushes 264 Commutator 265 Commutation 265 Armature 267 Armature Two-Layer Winding 268 Armature Reaction 268 Armature Reaction in Generator With Field Windings 269 Compensating Windings and Interpoles 270 Motor Reaction in a Generator 271 Armature Losses 272 Terminal Voltage 275 Field Excitation 276 Series Wound Generator 278 Shunt Wound Generator 279 Compound Wound Generators 280 DC Motors 282 2024-01-23 B-03a Electrical Fundamentals Page 10 of 302 CASA Part 66 - Training Materials Only  Inducing a Force on a Conductor 282 Principles of Operation 282 Torque 284 Torque in a DC Motor 286 Commutator and Brushes on a DC Motor 286 Counter-EMF 287 DC Motor Types 289 Motor Types 289 Series Motor 289 Series Motor Speed Control 290 Shunt Motor 291 Compound Motors 294 Separately Excited Motor 296 DC Motor Characteristics 297 Reversing Motor Direction 298 Armature Reaction in DC Motors 299 Cancelling Armature Reaction 300 Starter Generators 301 2024-01-23 B-03a Electrical Fundamentals Page 11 of 302 CASA Part 66 - Training Materials Only  Electron Theory (3.1) Learning Objectives 3.1.1 Recall the structure and distribution of electrical charges within atoms, molecules, ions and compounds (Level 1). 3.1.2 Recall the molecular structure of conductors, semiconductors and insulators (Level 1). 2024-01-23 B-03a Electrical Fundamentals Page 12 of 302 CASA Part 66 - Training Materials Only  Electron Theory Atoms All materials are made up of atoms. The atoms contribute to the electrical properties of a material, including its ability to conduct electrical current. For the purpose of discussing electrical properties, an atom can be represented by the valence shell and a core that consists of all the inner shells and the nucleus. This concept has been demonstrated in the Carbon atom below. The key features are: The Nucleus (at the centre of the atom) - containing both protons and neutrons. Electron shells (also referred to as rings) - containing electrons. © Aviation Australia Carbon Atom The charges of these atomic elements are as follows: Protons – positively charged Neutrons – neutrally charged Electrons – negatively charged. 2024-01-23 B-03a Electrical Fundamentals Page 13 of 302 CASA Part 66 - Training Materials Only  © Aviation Australia Atomic structure All elements follow this foundational structure, containing protons, neutrons and electrons, but not all elements conduct electricity. Electricity is defined as the flow of electrons between atoms and therefore a materials conductivity is determined by its willingness to share electrons. A material that can easily conduct electricity (or share electrons) is known as a conductor. A material that doesn't conduct electricity is known as an insulator. A third material type, that can range between both a conductor and an insulator is known as a semiconductor. 2024-01-23 B-03a Electrical Fundamentals Page 14 of 302 CASA Part 66 - Training Materials Only  Electron Shells Electrons occupy electron shells (or orbits), each of which are located at a certain distance from the nucleus. Each of the electrons in a particular electron shell possess a discrete amount of energy. Some atoms can have up to seven electron shells. Electrons with the least amount of energy are in the electron shell closest to the nucleus and electrons that possess the greatest amount of energy are in the shell furthest from the nucleus. The electron's that are further away from the nucleus are also held more weakly by the nucleus forces, and thus can be removed by spending less energy. Hence we say that these electrons are "loosely bound" to the atom. The outermost shell of the atom is known as the valence shell and contains the valence electrons. Each electron shell corresponds to a different energy level and (the first four shells) are labelled by the letters K, L, M and N. © Aviation Australia Electron Orbits 2024-01-23 B-03a Electrical Fundamentals Page 15 of 302 CASA Part 66 - Training Materials Only  Energy Levels Energy levels and electron shells are commonly used interchangeably. Both of these terms correspond to a fixed distance from the nucleus where the electrons are most likely to be found. The energy levels increase at each shell outward from the nucleus. Each successive shell can only hold a certain number of electrons. In the diagram below the electron shell capacities are 2, 8, 18 and 32 respectively (the first shell can hold 2 electrons, the second 8 and so on). The rules that dictate the total number of electrons in which a shell can hold varies from atom to atom and requires a deeper understanding of chemistry - beyond that which is required for this module. © Aviation Australia Electron energy levels (first four levels) In Aviation, electron theory is focused on the atomic valence shell and how it enables conduction and current flow. A knowledge of the detailed inner workings of an atom and how electrons behave beyond the valence shell may not be required, however a thorough understanding of certain materials that conduct and insulate electricity and why they do so is required. Importantly, the outermost shell of the atom is the valence shell and forms a significant energy band known as the valence band. This valence band determines whether or not an atoms electrons will flow (easily). 2024-01-23 B-03a Electrical Fundamentals Page 16 of 302 CASA Part 66 - Training Materials Only  Electron Flow A balanced atom has an equal number of protons and electrons. In the balanced state, an atom will always have an equal number of protons and electrons, and thus will have a net charge of zero. Hydrogen (1 Proton and 1 Electron) All matter contains energy, and the energy in an atom causes the electrons to spin around the nucleus. As the electrons spin, the centrifugal force tends to pull them away from the nucleus. However, the electrostatic attraction between the protons and the electrons produces a force which opposes the centrifugal force and holds the electrons in a specific orbit. A balanced atom's electrons will remain in their orbits as long as nothing upsets this balance. Positive electrical forces outside an atom can disrupt the balance and will tend to attract or 'steal' electrons from the outer ring. This outside electrical force could be caused by effects such as static friction, passing a wire through a magnetic field or from a chemical reaction (like within a dry cell battery). Other free electrons move to fill the space vacated by the first free electron. When this conditions occurs continuously, the movement of electrons becomes an electron flow known as current. © Aviation Australia Electron flow The result of gaining or losing electrons leaves the atom in an unbalanced electrostatic condition with an electrical charge. Charged atoms are called ions. If an atom has too many electrons, it is a negatively charged ion, and if it has too few electrons, it is a positively charged ion. The amount of energy that it takes for an atom to become negatively or positively charged is determined by the electrons in valence band of an atom. 2024-01-23 B-03a Electrical Fundamentals Page 17 of 302 CASA Part 66 - Training Materials Only  All electrons are alike, as are all protons and all neutrons. The structure, number and arrangement of these subatomic particles is what makes atoms differ from each other. For example, the simplest atom - a Hydrogen atom, has only one proton and one electron with only one electron shell (shown above). In contrast, the nucleus of a copper atom has 29 protons with 29 electrons orbiting the nucleus spread across four shells (shown below). © Aviation Australia Copper atom (29 Protons and 29 Electrons) Both hydrogen and copper are examples of atoms in a balanced state because they contain exactly the same number of protons (positive) and electrons (negative). The neutrons have no effect on the flow of electricity. 2024-01-23 B-03a Electrical Fundamentals Page 18 of 302 CASA Part 66 - Training Materials Only  Energy Bands The valence band of an atom contains the valence electrons. When an electron in the valence band acquires enough additional energy, it can leave the valence shell and become a free electron. A free electron exists in what is known as the conduction band. The difference in energy between the valence band and the conduction band is called an energy gap (also referred to as band gap). This is the amount of energy that a valence electron must have in order to jump from the valence band to the conduction band. Once in the conduction band, the electron is free to move throughout the material and is not tied to any given atom. The illustration below shows energy diagrams for insulators, semiconductors and conductors. © Aviation Australia Energy Bands in the three material types Insulators have a very large band gap. Valence electrons do not jump into the conduction band except under breakdown conditions where extremely high voltages are applied across the material. Semiconductors have a much narrower energy gap. This gap permits some valence electrons to jump into the conduction band and become free electrons, by adding energy such as heat. By contrast the energy bands in conductors overlap. In a conductive material there is always a large number of free electrons. 2024-01-23 B-03a Electrical Fundamentals Page 19 of 302 CASA Part 66 - Training Materials Only  Ions Normal atoms have a neutral charge, that is, they contain the same number of positively charged protons as negatively charged electrons. An ion is an atom that has lost or gained electrons. Its charge is positive if the atom has lost electrons and negative if the atom has gained electrons. A neutral atom and positive and negative ions For example, Copper (Cu) contains 29 electrons in it's neutral state. It is possible for copper to become ionised. Two common ions of copper are Copper (1+) and Copper (2+). Copper (1+) - Copper with one additional positive charge is known as the Cuprous ion (Cu+). Copper (2+) - Copper with two additional positive charges is known as the Cupric ion (Cu2+). Any atom which gains or loses electrons becomes an ion, so each element may have variations in both the positive and negative direction. Neon Lights A common practical use of ionisation is in Neon lighting. The group of elements on the periodic table which are known to be the most stable are called the noble gases. The noble gases contain the maximum number of valence electrons in their filled valance shell and are unreactive to other elements (under normal conditions). Neon (Ne) is one of these noble gases. A neon light is a sealed glass tube filled with neon gas that when ionised by high voltage, conducts electric current. This conduction can be used to produce light and in the case of Neon, produce red light. The different noble gases can be used to produce different colours. 2024-01-23 B-03a Electrical Fundamentals Page 20 of 302 CASA Part 66 - Training Materials Only  Molecules A molecule is two or more atoms bonded together and is the smallest particle to which a substance can be reduced and retain its characteristics. Electrically, a molecules conductivity depends on the bonded elements. Generally, ionic bonds join metals to nonmetals, covalent bonds join nonmetals to nonmetals and metallic bonds are responsible for the bonding between metal atoms. The metallic bonding that occurs between different metals, forms an alloy. Aluminum foil and copper wire are examples of metallic bonding in action and are known for conducting electricity well. Molecular structure of a nicotine molecule - C10 H14 N2 2024-01-23 B-03a Electrical Fundamentals Page 21 of 302 CASA Part 66 - Training Materials Only  Compounds A compound is matter in which all the molecules are identical, but the molecules are comprised of different atoms in exact proportions. Two or more individual elements combine to form a separate substance whose characteristics may be completely different from the original elements’ characteristics. Molecule vs Compound Molecule is the general term used to describe any atoms that are connected by chemical bonds. Every combination of atoms is a molecule. A compound is a molecule made of atoms from different elements. All compounds are molecules, but not all molecules are compounds. Water is a compound because it is made up of hydrogen and oxygen atoms (H2O). Carbon dioxide (CO2) and common salt, sodium chloride (NaCl), are also compounds. © Aviation Australia Water Molecule 2024-01-23 B-03a Electrical Fundamentals Page 22 of 302 CASA Part 66 - Training Materials Only  Electrical Properties of Molecules and Compounds Compounds that conduct a current are held together by electrostatic forces. They contain a positively charged atom (or molecule), known as a cation, and a negatively charged atom (or molecule), known as an anion. In their solid state, compounds do not conduct electricity, but when dissolved in water, the ions dissociate and can conduct a current. At high temperatures, when these compounds become liquid, the cations and anions begin to flow and can conduct electricity without water. Non-ionic compounds, or compounds that do not dissociate into ions, do not conduct a current. You can construct a simple circuit with a light bulb as an indicator to test the conductivity of aqueous compounds. The test compound in this setup will complete the circuit and turn on the light bulb if it can conduct a current. Typically, it is understood that water and electricity do not mix, ever. However, pure water is in fact an insulator and does not conduct electricity. It is the impurities that are introduced to water which make it conductive. When salts and other inorganic chemicals dissolve in water, they break into ions. The water that is seen in nature and the water that we use in our daily life contains several impurities and charged ions which makes it a very good conductor of electricity. An electrolyte is defined as any liquid or gel which contains ions and can be decomposed by electrolysis. Karishma50, CC BY-SA 4.0, via Wikimedia Commons Some compounds may conduct electricity where others may not To describe the compounds in the diagram (above), ethanol is an alcohol made up of carbon, hydrogen and oxygen and is an insulator. Potassium chloride (KCl which is also known as potassium salt) when dissolved in water makes an excellent conductor. And, acetic acid, which is the main component of vinegar is also a compound of carbon, hydrogen and oxygen and is a poor conductor of electricity. 2024-01-23 B-03a Electrical Fundamentals Page 23 of 302 CASA Part 66 - Training Materials Only  Compounds with Strong Conductivity The easiest way to determine whether a compound can conduct a current is to identify its molecular structure. Compounds with strong conductivity dissociate completely into charged atoms or molecules, or ions, when dissolved in water. These ions can move and carry a current effectively. The higher the concentration of ions, the greater the conductivity. Table salt, or sodium chloride, are examples of compounds with strong conductivity. It dissociates into positively charged sodium and negatively charged chlorine ions in water. Compounds with Weak Conductivity Compounds that dissociate only partially in water are weak electrolytes and poor conductors of an electric current. Acetic acid which is the compound present in vinegar, is a weak electrolyte because it dissociates slowly in water. 2024-01-23 B-03a Electrical Fundamentals Page 24 of 302 CASA Part 66 - Training Materials Only  Conductors, Insulators and Semiconductors Conductors The most commonly used conductors are single-element materials, such as copper, silver, gold and aluminium, which are characterised by atoms that have a single valence electron very loosely bound to the atom. These valence electrons can move freely around the conductor due to the overlap in the energy level of valence and conduction electrons. A conductive material has many free electrons that, when moving in the same direction, make up the electric current. © Aviation Australia Good conductors have 1-3 electrons in the outer (valence) shell The atomic number of the elements have been included in the diagram above. Recall that the atomic number is the number of protons in the nucleus of an atom. In a neutral or balanced atom the number of protons always equals the number of electrons. The electron counts for each shell can be identified with the valence electrons (the furthest right number) in these conductors being between 1 and 3. Copper (Cu) is the most commonly used conductor due to it's availability and price (in comparison with silver and gold) and is commonly used as wire in electric circuits. Copper has only one valence electron. When a positive force is applied, the valence electron is drawn away, leaving the atom positively charged. The atom now has more protons than electrons, thus creating a positive ion. The now positive ion tries to attract electrons from surrounding atoms. 2024-01-23 B-03a Electrical Fundamentals Page 25 of 302 CASA Part 66 - Training Materials Only  © Aviation Australia Electron flow in a copper wire Insulators An insulator is any material that inhibits (stops) the flow of electrons (electricity). An insulator is any material with five to eight free electrons in its valence shell. Aviation Australia An insulator has 5-8 electrons in the valence shell Because electrons in atoms with this number in the valence shell are held (bound) tightly to the atom, they cannot be easily moved to another atom or make room for more electrons. Some common insulators are glass, air, plastic, rubber, and wood. Rubber (natural rubber), for example, is a hydrocarbon and made up of hydrogen atoms and carbon atoms. In rubber, the electrons are tightly bound within the material, which means that they are not free to be shared by neighboring atoms. This is why rubber and it's variants are commonly used as the insulators around copper wiring. 2024-01-23 B-03a Electrical Fundamentals Page 26 of 302 CASA Part 66 - Training Materials Only  Semiconductors A semiconductor is a material which can act as both an insulator and a conductor. The nature of a semiconductor makes it an extremely useful tool in electronics. Semiconductors are employed in various kinds of electronic devices, including diodes, transistors, and integrated circuits. A semiconductor has four electrons in its valence shell. The two most common semiconductor elements exists in this configuration: silicon (Si) and germanium (Ge). Gallium arsenide (GaAs) is another common semiconductor material, however unlike silicon and germanium it is compound rather than an element. Carbon is also a semiconductor, it conducts electricity in some of its forms, such as graphite, but it doesn't conduct nearly as well as metals like copper or gold. In forms such as diamond, carbon is an insulator. © Aviation Australia Semiconductor atomic structure (4 electrons in valence shell) Silicon and germanium have four electrons in their valence shell which allows them to form a crystalline (crystal) structure. Silicon is abundantly available in quartzite. Extraction, purification, and crystallization processes for silicon are both efficient and economical. It is what makes silicon the most common semiconductor element in the world. The four electrons form perfect covalent bonds (i.e. the attraction/repulsion stability that forms between atoms when they share electrons) with four neighbouring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance. 2024-01-23 B-03a Electrical Fundamentals Page 27 of 302 CASA Part 66 - Training Materials Only  Aviation Australia Silicon structure with good semiconductor properties As electricity involves the flow of electrons, metals tend to be good conductors of electricity because they have 'free electrons' that can move easily between atoms. While silicon crystals look metallic, they are not in fact metals. All of the outer electrons in a silicon crystal are involved in perfect covalent bonds, so they can't move around. A pure silicon crystal is nearly an insulator – very little electricity will flow through it. Neither silicon nor germanium will conduct electricity. This is due to the number of electrons in the valence shell, combined with the strong covalent bonds formed when valence electrons in one atom mix with those in another. The process that changes the behaviour of silicon or germanium to allow conduction is known as doping. 2024-01-23 B-03a Electrical Fundamentals Page 28 of 302 CASA Part 66 - Training Materials Only  Static Electricity and Conduction (3.2) Learning Objectives 3.2.1.1 Describe the nature, causes and effects of static electricity (Level 2). 3.2.1.2 Describe the distribution of electrostatic charges in materials, the effect of electrostatic charge imbalance (Level 2). 3.2.1.3 Describe the methods for dissipation of accumulated static charges in aircraft (Level 2). 3.2.2 Describe the laws of electrostatic attraction and repulsion (Level 2). 3.2.3.1 Describe the units of electrostatic charge (Level 2). 3.2.3.2 Explain Coulomb's Law (Level 2). 3.2.4.1 Describe how conduction of electricity occurs in solids (Level 2). 3.2.4.2 Describe how conduction of electricity occurs in liquids (Level 2). 3.2.4.3 Describe how conduction of electricity occurs in gases (Level 2). 3.2.4.4 Describe how conduction of electricity occurs in vacuum (Level 2). 2024-01-23 B-03a Electrical Fundamentals Page 29 of 302 CASA Part 66 - Training Materials Only  Static Electricity Static Charge All matter is made up of atoms, which are themselves made up of charged particles (electrons and protons). Protons are positively charged, the electrons are negatively charged, and the neutrons are neutral. Opposite charges attract (positive to negative) and like charges repel (positive to positive or negative to negative). Most of the time, these charges are balanced within an atom, which makes the atom neutral. An atom may be balanced, positively charged or negatively charged Static electricity is the result of an imbalance between negative and positive charges in a material. These charges can build up on the surface of an object until they find a way to be released or discharged. Examples of static discharge include lightning and the shock that is sometimes felt upon touching another object (like a car door). The rubbing of certain materials against one another can transfer negative charges, or electrons. Some materials at an atomic level hold on to their electrons more tightly than others do. The strength in which matter holds on to it's electrons determines its place in the triboelectric series. If a material is more apt to give up electrons when in contact with another material, it is more positive in the triboelectric series. If a material is more apt to 'capture' electrons when in contact with another material, it is more negative in the triboelectric series. 2024-01-23 B-03a Electrical Fundamentals Page 30 of 302 CASA Part 66 - Training Materials Only  Triboelectric Effect Friction, pressure and separation are the major causes of static electricity. This process is called the triboelectric effect (tribo means 'rubbing'). It is a type of contact electrification in which certain materials become electrically charged after coming into contact with another different material, and are then separated. The triboelectric effect between two materials The electrons are transferred from one substance to another following contact, friction and separation. Friction is caused by contact and pressure between materials The magnitude of the static charge is determined by the material composition, the applied forces, the separation rate and the relative humidity. Environmental variables like relative humidity influence the level of electrostatic charges. When humidity is low, higher static charges are generated. Static becomes more noticeable in the winter months, in dry climates and in air-conditioned environments. Increasing humidity to 60% limits static build-up because surface moisture on materials makes a good conductor. Unfortunately, 60% relative humidity is extremely uncomfortable, can cause equipment problems and can introduce contaminants into your system. 2024-01-23 B-03a Electrical Fundamentals Page 31 of 302 CASA Part 66 - Training Materials Only  Means of static Electrostatic Voltages at 10% to Electrostatic Voltages at 65% to generation 20% relative humidity 90% relative humidity Walking across carpet 35 000 1 500 Walking over vinyl floor 12 000 250 Worker at a bench 6 000 100 Vinyl envelopes for work 7 000 600 instructions Plastic bag picked up 20 000 1 200 from bench Chair padded with 18 000 1 500 polyurethane foam Triboelectric Series Aviation Australia Triboelectric series positive and negative static generation 2024-01-23 B-03a Electrical Fundamentals Page 32 of 302 CASA Part 66 - Training Materials Only  The triboelectric series is a list that ranks materials according to their tendency to gain or lose electrons. Materials higher on the triboelectric series become positively charged (lose electrons), those lower in the series become negatively charged (gain electrons) and the elements in the centre are neutral. The voltage levels generated when two materials are rubbed together can be predicted as those materials close together in the series will produce less voltage than those further apart in the series. Coulomb’s Law of Charges The relationship between attracting or repelling charged bodies was first discovered and written about in the 1780s by a French scientist named Charles A. Coulomb. Coulomb's Law Charged bodies attract or repel each other with a force that is directly proportional to the product of their individual charges, and is inversely proportional to the square of the distance between them. The amount of attracting or repelling force which acts between two electrically charged bodies in free space depends on two things: 1. Their charges, and 2. The distance between them. The strength of attracting and repelling forces varies inversely with the square of the distance between the two charges. For example, if the distance between two objects with dissimilar charges is doubled, the force of attraction is reduced to one fourth of its original value. If the distance between the two objects is tripled, the force of attraction becomes one ninth of its original value. On the other hand, if the distance between the objects is halved, the force of attraction increases fourfold. The interaction between charged objects is a non-contact force which acts over some distance of separation. There are always two charges and a distance between them as the three critical variables which influence the strength of the interaction. Aviation Australia Interaction of two charged particles 2024-01-23 B-03a Electrical Fundamentals Page 33 of 302 CASA Part 66 - Training Materials Only  Coulomb's Law Equation q1q2 F = ke 2 s Where Ke is the Coulomb constant, q1 and q2 are the signed magnitudes of the charges, and s is the distance between the charges. The unit for quantities of electric charge is the Coulomb. Symbol for coulombs is C. Symbol for charge is Q. 1 coulomb = 6.25 x 1018 electrons. In electricity, the practical unit of electrical charge is the coulomb, which is equal to the electric charge of approximately 6.25 × 1018 electrons. The coulomb measures the quantity of electric charge, or the number of electrons, regardless of whether the charge is moving or not. Distribution of Electrostatic Charges Materials that bear imbalances of opposite charge will attract each other and cling together. Materials that bear imbalances of like charge will repel each other. When an object bearing an enormous accumulation of positive or negative charge comes close to another object bearing the opposite charge, a spark may jump across the space between them. This can result in both the enormously powerful discharges of lightning and the small yet stimulating shocks we receive when touching something after shuffling across a carpet in our stocking feet. Because wool cloth is a material that readily gives up electrons, it is used in many activities to produce an accumulation of negative charge on an otherwise neutral object. Human hair is another common material that readily gives up electrons. Materials of opposite charge will attract each other 2024-01-23 B-03a Electrical Fundamentals Page 34 of 302 CASA Part 66 - Training Materials Only  Electrostatic Attraction and Repulsion An uncharged pith (painted styrofoam) ball is attracted to a rod which is positively or negatively charged. Regardless of the polarity of the charged rod, because the pith ball is neutral, it will always react as an opposite polarity. For example, if the rod has lost electrons and is positive, the neutral pith ball will be of negative polarity with respect to the rod. So the rod being positive and the ball being negative (with respect to the rod) will cause the ball to be attracted. The attraction will still occur if the rod has an excess of electrons and is negatively charged. In this case, the ball will appear to be positively charged with respect to the rod, so it will again be attracted. Once the rod touches the ball, electrons flow to establish an even balance, and when both the rod and the pith ball exhibit like electrostatic charges, they repel each other. A material such as rubber is known as an electrical insulator. Accumulations of charge will not move across the surface of a rubber object easily. When one part of a balloon is rubbed with wool, the wool gives up electrons, making that part of the balloon negatively charged even though the rest of the balloon may remain neutrally charged. When a charged object, such as a balloon that has been rubbed with wool, is brought near a neutrally charged object, such as a piece of Styrofoam, the Styrofoam is said to become positively charged by induction and may leap towards the charged balloon. An object charged by induction does not actually have to lose or gain electrons. A negatively charged balloon brought near a neutrally charged piece of Styrofoam repels the electrons on the surface of the Styrofoam. The repelled electrons migrate as far away from the balloon as possible. This leaves the near end of the Styrofoam with an imbalance of positive charge and results in the attraction of the Styrofoam to the balloon. Attraction of opposite and repulsion of like charges 2024-01-23 B-03a Electrical Fundamentals Page 35 of 302 CASA Part 66 - Training Materials Only  Dissipation of Accumulated Charges The feature of charge accumulation at points is used to advantage on some aircraft. Unwanted charge that dissipates during flight is dissipated into the atmosphere by discharge wicks. These are located where the air friction can pick off the charge concentrated on them. They are designed, and their location on the aircraft is selected, to minimise the interference with aircraft radio performance that may otherwise be caused by uncontrolled random discharges. Distribution of static charges on different materials and shapes Discharge wicks are usually fitted to large aircraft, but seldom to small ones. This is because less charge accumulates on smaller aircraft. Static discharge wicks on the trailing edges of an aircraft wing 2024-01-23 B-03a Electrical Fundamentals Page 36 of 302 CASA Part 66 - Training Materials Only  Conduction of Electricity in Materials Conduction of Electricity in Solids In solid conductors made of various metals – silver being the best, closely followed by gold, aluminium and copper – these materials have a large number of free electrons readily available to move from atom to atom. When an electrical force (EMF) is applied to the metal, it attracts these free electrons from their outer orbits and starts a domino effect with electrons jumping from atom to atom. The result is that the electricity reaches the other end of the conductor at the speed of light even though the individual electrons move between atoms. This is called conduction current. Solid conductor electron flow An electron leaves the negative terminal of the battery and knocks another electron out of an atom in the conductor. This free electron in turn knocks an electron out of another atom and takes its place. At the other end of the conductor cable the negatively charged electrons in the conductor are attracted to the positive battery terminal. Electricity is conducted through solids via movement of electrons. Copper is the material most commonly used as a conductor. Brass, aluminium and carbon are also used often, and although silver and gold are better conductors than these, they are used only in special applications because of their high cost. The descending order of conductivity is silver, copper, gold, aluminium, brass and then carbon. 2024-01-23 B-03a Electrical Fundamentals Page 37 of 302 CASA Part 66 - Training Materials Only  © Aviation Australia Copper wire is the most common conductor used in electrical cable Although most metals do not conduct electricity as effectively as the above-mentioned metals, all metals are reasonably good conductors. Many are rarely produced specifically as conductors, but when they are part of the assemblies manufactured for some other primary purpose, they may also be used as conductors. Examples of this are the use of steel, aluminium and other metals in aircraft and automobile structures and engines as conducting mediums, particularly as an earth or return path. Electron flow (animated) 2024-01-23 B-03a Electrical Fundamentals Page 38 of 302 CASA Part 66 - Training Materials Only  Relative Resistances of Solid Conducting Materials In practice it is more usual to think of conductors’ and components’ resistance (commonly referred to as resistivity) rather than their conductance. Copper, with a datum of 1, is used as a baseline by which to compare other materials’ resistance. Adapted from Brandes, E. A., Ed., Smithells Metals Reference Book, Sixth Edition, Butterworth Inc. 1983 Electrical resistivity of copper and other pure Metals at 20 degrees Celcius Carbon is the only non-metal solid that has significance as a conductor. Although carbon has a resistance 2000–3000 times that of copper, its self-lubricating quality makes it the most suitable material for a rubbing connection with commutators or slip rings (which are usually manufactured from copper) used in generators and alternators. 2024-01-23 B-03a Electrical Fundamentals Page 39 of 302 CASA Part 66 - Training Materials Only  Conduction of Electricity in Liquids When current is passed through some liquids, it creates what we call ions, atoms of liquid or gas that have either gained or lost an electron. If an atom gains an electron, it has an overall negative charge (more electrons than protons) and is called a negative ion. If it loses an electron, it has an overall positive charge (fewer electrons than protons) and is called a positive ion. Ions - atoms of liquid or gas that have either gained or lost an electron In a liquid, it is not so much atoms which are ionised, but rather groups of atoms called molecules. Negatively charged ions move in one direction and positively charged ions move the opposite way. The charges they carry are given up at the appropriate electrodes. Usually when this process occurs, the liquid will be caused to break down into its component parts or, in some cases, one of the metal electrodes will be eaten away. Ionic substances are made of charged particles – ions. When the ionic solid is dissolved in water, the ionic lattice breaks up and the ions become free to move around in the water. When electricity is passed through the ionic solution, the ions are able to carry the electric current because of their ability to move freely. A solution conducts by means of freely moving ions. Conductivity of Liquids Liquids which are able to conduct ionically are known as electrolytes. It is the chemical nature of these liquids to form positive and negative ions. Most electrolytes are acid, alkali or salt solutions. 2024-01-23 B-03a Electrical Fundamentals Page 40 of 302 CASA Part 66 - Training Materials Only  Solution Conductivity Pure water (distilled) non Tap water poor Pool or sea water weak Soluble salt solution (NaCl) strong Strong acids strong Weak acids weak Strong bases strong Weak bases (Ammonia) weak Molecular compounds (sugar solution) non If positive and negative electrodes are placed in an electrolyte, the positive and negative ions will naturally be attracted to the opposite-polarity electrodes. The ionic transfer of electric charge is a conduction of current. When ions reach the electrodes, depending on their polarity, they either give or receive electrons, thus contributing to the electron transfer of charge through the solid conducting circuit external to the electrolyte. 2024-01-23 B-03a Electrical Fundamentals Page 41 of 302 CASA Part 66 - Training Materials Only  Electrodes in an electrolyte solution of molten lead bromide 2024-01-23 B-03a Electrical Fundamentals Page 42 of 302 CASA Part 66 - Training Materials Only  Conduction of Electricity in Gases In their normal state gases are insulators, but when ionised they become conductors. Heat or high electrical potentials can dislodge electrons from, or cause electrons to move into, the atoms or molecules of a gas. Ions are thus formed and the gas is said to be ionised; in this condition, the resistance of the gas is markedly decreased. Ionisation occurs across the gap of spark plugs in piston engines, in fluorescent and gas discharge lamps, and in the air path of a lightning discharge. © Aviation Australia Ionisation in the spark of an engine spark plug 2024-01-23 B-03a Electrical Fundamentals Page 43 of 302 CASA Part 66 - Training Materials Only  Thermionic Emission Thomas Edison discovered the principle of thermionic emission as he looked for ways to keep soot from clouding his incandescent light bulb. Edison placed a metal plate inside his bulb along with the normal filament. He left a gap, a space, between the filament and the plate. He then placed a battery in series between the plate and the filament, with the positive side towards the plate and the negative side towards the filament. When Edison connected the filament battery and allowed the filament to heat until it glowed, he discovered that the ammeter in the filament-plate circuit had deflected and remained deflected. He reasoned that an electrical current must be flowing in the circuit – even across the gap between the filament and plate. Edison could not explain exactly what was happening. At that time, he probably knew less about what makes up an electric circuit than you do now. Because it did not eliminate the soot problem, he did little with this discovery. However, he patented the incandescent light bulb and made it available to the scientific community. Thermionic emission or The Edison Effect Let's analyse the circuit. You probably already have a good idea of how Edison’s circuit works. The heated filament causes electrons to boil from its surface. The battery in the filament-plate circuit places a positive charge on the plate (because the plate is connected to the positive side of the battery). The electrons (negative charge) that boil from the filament are attracted to the positively charged plate. They continue through the ammeter and battery, and then back to the filament. You can see that electron flow across the space between filament and plate is actually an application of a basic law you already know: unlike charges attract. 2024-01-23 B-03a Electrical Fundamentals Page 44 of 302 CASA Part 66 - Training Materials Only  Edison's bulb had a vacuum so the filament would glow without burning. Also, the space between the filament and plate was relatively small. The electrons emitted from the filament did not have far to go to reach the plate. Thus, the positive charge on the plate was able to attract the negative electrons. © Aviation Australia Thermionic emission in the light bulb The key to this explanation is that the electrons were floating free of the hot filament. It probably would have taken hundreds of volts to move electrons across the space if they had to be forcibly pulled from a cold filament. Such an action would destroy the filament and the flow would cease. Edison’s application of thermionic emission in causing electrons to flow across the space between the filament and the plate has become known as the Edison effect. Metallic conductors contain many free electrons, which at any given instant are not bound to atoms. These free electrons are in continuous motion. The higher the temperature of the conductor, the more agitated the free electrons, and the faster they move. A temperature can be reached at which some of the free electrons become so agitated that they actually escape from the conductor. They 'boil' from the conductor's surface. The process is similar to steam leaving the surface of boiling water. Heating a conductor to a temperature sufficiently high that it causes the conductor to give off electrons is called thermionic emission. 2024-01-23 B-03a Electrical Fundamentals Page 45 of 302 CASA Part 66 - Training Materials Only  Conduction of Electricity in a Vacuum Conduction of current in a vacuum is much more difficult to achieve because there are no gas molecules which can liberate free electrons. It requires a cathode (negative electrode) to be forced to release electrons either by heating it up (thermionic emission) or by using a high voltage to strip electrons out of it, as in a thermionic valve (radio valve) or cathode ray tube of the television or oscilloscope type. This stream of electrons will then pass across the tube to the anode, which has a high positive potential (25 000 volts is not uncommon in TV sets). Electrons are emitted from a cathode by thermionic emission (heating of conductor) and stream across to the plate (anode) because of electrostatic attraction. © Aviation Australia Conduction of electricity in a vacuum 2024-01-23 B-03a Electrical Fundamentals Page 46 of 302 CASA Part 66 - Training Materials Only  Electrical Terminology (3.3) Learning Objectives 3.3.1 Describe potential difference and the factors affecting it (Level 2). 3.3.2 Describe electromotive force and the factors affecting it (Level 2). 3.3.3 Identify the units of voltage and the factors affecting it (Level 2). 3.3.4 Identify the units of current and the factors affecting it (Level 2). 3.3.5 Identify the units of resistance and the factors affecting it (Level 2). 3.3.6 Identify the units of conductance and the factors affecting it (Level 2). 3.3.7 Identify the units of electric charge and the factors affecting it (Level 2). 3.3.8 Describe conventional current flow and the factors affecting it (Level 2). 3.3.9 Describe electron flow and the factors affecting it (Level 2). 2024-01-23 B-03a Electrical Fundamentals Page 47 of 302 CASA Part 66 - Training Materials Only  Electrical Terminology Electric Charge The coulomb is the unit for quantities of electric charge transferred between points of different electrical potential. © Aviation Australia Coulombs The coulomb is the electric charge equivalent to a definite number of electrons (6.24 × 1018). The symbol for coulombs is C. Q (or lowercase q) is used as the symbol for charge. Q = 3 C or q = 3 C Q = 3C means a charge of three coulombs. 2024-01-23 B-03a Electrical Fundamentals Page 48 of 302 CASA Part 66 - Training Materials Only  Electric Current Charge may be transferred between points of different potential at varying rates of flow. The rate of transfer is measured in coulombs per second, and 1 C/s is one ampere. The ampere is the unit of current. If 1 C flows through a circuit each second, the current is one ampere; 10 C/s is 10 amperes. Amp is the abbreviation for ampere. The symbol for amperes is A and I is the symbol for current. I = 3 A or i = 3 A I = 3 A means a current of three amps. Electric Current Flow Conventions According to the electron theory, the current always flows from the most negative point to the most positive point. Therefore, if a conductor is connected between the terminals of a power source, that is, a battery or generator, a current will flow from the negative terminal (-) to the positive terminal (+). Before scientists understood the true nature of the structure of the atom, electricity had already been in use for a long time even though no-one knew how or why it worked. It was assumed that, like water, charges of some type moved from a point of high pressure (+) to a point of low pressure (-). If the pressure difference was great, then the flow was great, and if the difference was small, so was the flow. This is known as the conventional current flow theory and is still in use in some textbooks even today. © Aviation Australia Electron flow vs conventional current 2024-01-23 B-03a Electrical Fundamentals Page 49 of 302 CASA Part 66 - Training Materials Only  For all your studies of electricity in this course, the electron theory (electron flow) and all the rules which have been devised for it will be used. Current flow, which is electron movement, is understood to occur from negative to positive. Electromotive Force/Voltage Voltage is a measure of the force or pressure that is applied to electrons to remove them from their orbits and propel them along a wire. Electric circuit It is usually called electromotive force, or EMF for short, so the statement that 12 volts are being applied to a circuit indicates the EMF being applied to move electrons down the wire. Current does work or expends energy when it overcomes resistance. As in all cases in which work is done, a force must perform the work. This force is EMF. The unit for this force is expressed in volts. The current in a circuit is proportional to the voltage driving it through the circuit. Doubling the voltage doubles the current, and halving the voltage halves the current. The symbol for volts is V. E is the symbol for EMF. E = 3 V means an electromotive force of 3 volts. 2024-01-23 B-03a Electrical Fundamentals Page 50 of 302 CASA Part 66 - Training Materials Only  Potential Difference Potential is denoted with reference to a point (e.g. +100 V with reference to 0 V). If we have two bodies, each at a different potential, then the voltage which is measurable between them is a measure of that difference in potential. It can have either a positive or negative sign, depending on the point of reference. Voltage can relate to different points of reference and so have a positive or negative sign. Even if one of the bodies has a zero charge, the other body can still relate to it as a positive or negative potential. Aviation Australia Potential difference between three independent bodies The voltage difference between two bodies is called the potential difference (PD) and is measured in volts. 2024-01-23 B-03a Electrical Fundamentals Page 51 of 302 CASA Part 66 - Training Materials Only  Aviation Australia EMF in a simple circuit Resistance The current in a circuit is inversely proportional to the resistance of the circuit. For circuits with a steady EMF, doubling the resistance halves the current, and halving the resistance doubles the current. Aviation Australia Resistance is a property that opposes current flow 2024-01-23 B-03a Electrical Fundamentals Page 52 of 302 CASA Part 66 - Training Materials Only  Resistance is directly proportional to the length of any conductor and inversely proportional to its cross-sectional area. Thus a 10-m length of copper wire has twice the resistance of a 5-m length of the same wire. If one copper wire has twice the cross-sectional area of the other, but the same length, the resistance will be half. The ohm is the unit of electrical resistance. The symbol for ohms is Ω. R is the symbol for resistance. R = 3 Ω means a resistance of three ohms. Factors Controlling Resistance Even the very best conductors have some resistance, which limits the flow of electric current through them. The resistance of any object, such as a wire conductor, depends on four factors: The material of which it is made Its length Its cross-sectional area Its temperature. For most materials, the hotter the material, the more resistance it offers to the flow of an electric current. Conversely, the colder the material, the less resistance it offers to the flow of an electric current. Ohm's Law The relationship between voltage, current and resistance can be described by Ohm's law. V = IR 2024-01-23 B-03a Electrical Fundamentals Page 53 of 302 CASA Part 66 - Training Materials Only  Conductance Conductance is the reciprocal of resistance. It is a rarely used term. The siemen is a unit for the measurement of a material’s ability to conduct current. 1 G = siemens R The symbol for siemens is S. The symbol for conductance is G. G = 3 S means a conductance of 3 siemens. 2024-01-23 B-03a Electrical Fundamentals Page 54 of 302 CASA Part 66 - Training Materials Only  Generation of Electricity (3.4) Learning Objectives 3.4.1 Describe typical methods by which electricity is generated using light (Level 1). 3.4.2 Describe typical methods by which electricity is generated using heat (Level 1). 3.4.3 Describe typical methods by which electricity is generated using friction (Level 1). 3.4.4 Describe typical methods by which electricity is generated using pressure (Level 1). 3.4.5 Describe typical methods by which electricity is generated using chemical action (Level 1). 3.4.6 Describe typical methods by which electricity is generated using magnetism and motion (Level 1). 2024-01-23 B-03a Electrical Fundamentals Page 55 of 302 CASA Part 66 - Training Materials Only  Generation of Electricity Voltage Produced by Friction The first method discovered for creating a voltage was generation by friction. The development of charges by rubbing a rod with fur is a prime example of the way friction generates voltage. Triboelectric effect Electrostatics is a subject with which most persons entering the field of electricity and electronics are somewhat familiar. For example, most have seen the way a person’s hair stands on end when turning on or off a TV tube, or when holding a balloon or plastic item near their head after vigorous rubbing. A Greek philosopher, Thales of Miletus, discovered that when a rod of amber was rubbed with fur, the rod attracted some very light objects such as paper and wood shavings. Other substances, such as glass, produce similar effects when rubbed with silk, ebonite or fur. William Gilbert, an English scientist, classified all the substances which possessed similar attracting properties as electrics, a word of Greek origin meaning 'amber'. Because of Gilbert's work with electrics, a substance such as amber or glass was recognised as being electrified or charged with electricity when given a vigorous rubbing. In a natural or neutral state, each atom of a material has a balanced number of protons and electrons. If electrons are removed, it will become electrically positive, and if the material gains electrons, it will be considered electrically negative. When two bodies of matter have unequal charges and are near one another, an electrical force is exerted between them. However, since they are not in contact, their charges cannot equalise. The existence of such an electric force where current cannot flow is referred to as static electricity, or electrostatic force. 2024-01-23 B-03a Electrical Fundamentals Page 56 of 302 CASA Part 66 - Training Materials Only  One of the easiest ways to produce a static charge is by friction. When two pieces of matter are rubbed together, electrons can be 'wiped off' one material and onto the other. If the materials used are good conductors, it is quite difficult to obtain a detectable charge on either because equalising currents can easily flow between the conducting materials. These currents equalise the charges almost as fast as they are created. A static charge is more readily created between materials that are not conductors. When a hard rubber rod is rubbed with fur, the rod will accumulate electrons given up by the fur. Since both materials are poor conductors, very little equalising current can flow and an electrostatic charge builds up. When the charge becomes great enough, the current will flow regardless of good conductivity of the materials. These currents will cause visible sparks and produce a crackling sound. Static electricity Other forms of static occur with rubber-soled boots on some carpets or in your car on dry, non-humid days. Get out of your car, and when you grab the door to close it, you will get a zap. To avoid this, grab the door, then place your foot on the ground. The spark will jump from your boot, not your finger. Because of the nature of the materials with which static electricity is generated, it cannot be conveniently used or maintained. For this reason, very little practical use has been found for voltages generated by this method. Static electricity is more of a nuisance than a useful form of electrical energy, and it creates some extremely dangerous situations. 2024-01-23 B-03a Electrical Fundamentals Page 57 of 302 CASA Part 66 - Training Materials Only  Static electricity is of real concern during fuelling operations, both aircraft and vehicular. The movement of the fuel through a fuel pipe has the same effect as rubbing a rod with a piece of fur (relative movement) and can build up huge potential differences. If an electrostatic spark emits at the point of the refuel, fuel vapours will ignite and an explosion will likely result. Always ensure all earth leads are serviceable and correctly utilised during refuelling operations. Filling vehicles and drums at service stations can also produce electrostatic sparks. When siphoning fuel, use only appropriate anti-static tubing. Aviation Australia Bonding during aircraft refuelling to reduce the fire risk Aircraft movement through the air can also build up huge potential charges on the aircraft skin, which can then cause electrostatic discharges when the aircraft returns to the ground. Aircraft utilise static discharge needles or wicks, positioned to minimise interference with radio systems and where friction can pick off the positive or negative charge. Static discharge wicks 2024-01-23 B-03a Electrical Fundamentals Page 58 of 302 CASA Part 66 - Training Materials Only  Voltage Produced by Pressure A specialised method of generating an EMF utilises the characteristics of certain ionic crystals, such as quartz. These crystals have the remarkable ability to generate a voltage whenever stresses are applied to their surfaces. Thus, if a quartz crystal is squeezed, charges of opposite polarity will appear on two opposite surfaces of the crystal. If the force is reversed and the crystal is stretched, charges will again appear, but will be of the opposite polarity from those produced by squeezing. If a crystal of this type is given a vibratory motion, it will produce a voltage of reversing polarity between two of its sides. Quartz or similar crystals can thus be used to convert mechanical energy into electrical energy. This phenomenon is called the piezoelectric effect. Quartz crystal Crystalline materials produce small amounts of electricity when a force is applied that changes their shape in some way. These are called piezoelectric materials. Piezoelectric effect (animation) Quartz is an example of a piezoelectric substance. When small amounts of pressure are applied to a quartz crystal, a small voltage is produced from the changing charge, created by the moving electrons. Phonographs with a crystal cartridge utilise the piezoelectric principle to convert the movement of the needle to an electrical signal, which is later amplified and played through speakers. Microphones and barbecue lighters also use this principle. 2024-01-23 B-03a Electrical Fundamentals Page 59 of 302 CASA Part 66 - Training Materials Only  Aviation Australia Piezoelectric effect on quartz This method of generating an EMF is not suitable for applications with large voltage or power requirements but is widely used in sound and communications systems, where small voltages can be effective. Crystals of this type possess another interesting property, the converse piezoelectric effect. That is, they have the ability to convert electrical energy into mechanical energy. A voltage impressed across the proper surfaces of the crystal will cause it to expand or contract its surfaces in response to the voltage applied. A piece of crystal vibrates at one natural frequency, and when a crystal is excited by pulses of electrical energy, it vibrates at this frequency. As it vibrates, it produces alternating voltage that has a specific frequency. Voltage Produced by Heat When a length of metal, such as copper, is heated at one end, valence electrons tend to move away fro