Module 3 covers all things electrical and looks at Electron theory, Static Electricity, Terminology, Generation DC sources & Circuits, Resistance, Capacitance, Magnetism, Inductance, AC theory, AC Generators & Motors
Detailed Content / Topics – The following Subjects will be addressed -
1. Electron Theory
– Structure and distribution of electrical charges within: atoms, molecules, ions, compounds;
– Molecular structure of conductors, semiconductors and insulators
2. Static Electricity and Conduction
– Static electricity and distribution of electrostatic charges;
– Electrostatic laws of attraction and repulsion;
– Units of charge, Coulomb’s Law;
– Conduction of electricity in solids, liquids, gases and a vacuum
3. Electrical Terminology
– The following terms, their units and factors affecting them: potential difference, electromotive force, voltage, current, resistance, conductance, charge, conventional current flow, electron flow.
4. Generation of Electricity
– Production of electricity by the following methods: light, heat, friction, pressure, chemical action, magnetism and motion.
5. DC Sources of Electricity
– Construction and basic chemical action of: primary cells, secondary cells, lead acid cells, nickel cadmium cells, other alkaline cells;
– Cells connected in series and parallel;
– Internal resistance and its effect on a battery;
– Construction, materials and operation of thermocouples; Operation of photo-cells
6. DC Circuits
– Ohms Law, Kirchoff’s Voltage and Current Laws;
– Calculations using the above laws to find resistance, voltage and current;
– Significance of the internal resistance of a supply.
– Resistance and affecting factors;
– Specific resistance;
– Resistor colour code, values and tolerances, preferred values, wattage ratings;
– Resistors in series and parallel;
– Calculation of total resistance using series, parallel and series parallel combinations;
– Operation and use of potentiometers and rheostats;
– Operation of Wheatstone Bridge;
– Positive and negative temperature coefficient conductance;
– Fixed resistors, stability, tolerance and limitations, methods of construction;
– Variable resistors, thermistors, voltage dependent resistors;
– Construction of potentiometers and rheostats;
– Construction of Wheatstone Bridge
– Power, work and energy (kinetic and potential);
– Dissipation of power by a resistor;
– Power formula;
– Calculations involving power, work and energy.
– Operation and function of a capacitor;
– Factors affecting capacitance area of plates, distance between plates, number of plates, dielectric and dielectric constant, working voltage, voltage rating;
– Capacitor types, construction and function;
– Capacitor colour coding;
– Calculations of capacitance and voltage in series and parallel circuits;
– Exponential charge and discharge of a capacitor, time constants;
– Testing of capacitors.
– Theory of magnetism;
– Properties of a magnet;
– Action of a magnet suspended in the Earth’s magnetic field;
– Magnetisation and demagnetisation;
– Magnetic shielding;
– Various types of magnetic material;
– Electromagnets construction and principles of operation;
– Hand clasp rules to determine: magnetic field around current carrying conductor;
– Magnetomotive force, field strength, magnetic flux density, permeability, hysteresis loop, retentivity, coercive force reluctance, saturation point, eddy currents;
– Precautions for care and storage of magnets
– Faraday’s Law;
– Action of inducing a voltage in a conductor moving in a magnetic field;
– Induction principles;Effects of the following on the magnitude of an induced voltage: magnetic field strength, rate of change of flux, number of conductor turns; Mutual induction;
– The effect the rate of change of primary current and mutual inductance has on induced voltage;
– Factors affecting mutual inductance: number of turns in coil, physical size of coil, permeability of coil, position of coils with respect to each other;
– Lenz’s Law and polarity determining rules;
– Back emf, self induction;
– Saturation point;
– Principle uses of inductors.
12. DC Motor/Generator Theory
– Basic motor and generator theory;
– Construction and purpose of components in DC generator;
– Operation of, and factors affecting output and direction of current flow in DC generators;
– Operation of, and factors affecting output power, torque, speed and direction of rotation of DC motors; – Series wound, shunt wound and compound motors;
– Starter Generator construction.
13. AC Theory
– Sinusoidal waveform: phase, period, frequency, cycle;
– Instantaneous, average, root mean square, peak, peak to peak current values and calculations of these values, in relation to voltage, current and power;
– Triangular/Square waves;
– Single/3 phase principles.
14. Resistive (R), Capacitive (C) and Inductive (L) Circuits
– Phase relationship of voltage and current in L, C and R circuits, parallel, series and series parallel; – Power dissipation in L, C and R circuits;
– Impedance, phase angle, power factor and current calculations;
– True power, apparent power and reactive power calculations
– Transformer construction principles and operation;
– Transformer losses and methods for overcoming them;
– Transformer action under load and no-load conditions;
– Power transfer, efficiency, polarity markings;
– Calculation of line and phase voltages and currents;
– Calculation of power in a three phase system;
– Primary and Secondary current, voltage, turns ratio, power, efficiency;
– Auto transformers.
– Operation, application and uses of the following filters: low pass, high pass, band pass, band stop.
17. AC Generators
– Rotation of loop in a magnetic field and waveform produced;
– Operation and construction of revolving armature and revolving field type AC generators;
– Single phase, two phase and three phase alternators;
– Three phase star and delta connections advantages and uses;
– Permanent Magnet Generators.
18. AC Motors
– Construction, principles of operation and characteristics of: AC synchronous and induction motors both single and polyphase;
– Methods of speed control and direction of rotation;
– Methods of producing a rotating field: capacitor, inductor, shaded or split pole.