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Table of Contents
                            Cover Page
Title Page
Copyright Page
Table of
Section 1: Basic Electrical and Electronic Engineering Principles
	Chapter 1. Units associated with basic electrical
		1.1 SI units
		1.2 Charge
		1.3 Force
		1.4 Work
		1.5 Power
		1.6 Electrical potential and e.m.f.
		1.7 Resistance and conductance
		1.8 Electrical power and energy
		1.9 Summary of terms, units and their symbols
	Chapter 2. An introduction to electric circuits
		2.1 Electrical/electronic system block diagrams
		2.2 Standard symbols for electrical components
		2.3 Electric current and quantity of electricity
		2.4 Potential difference and resistance
		2.5 Basic electrical measuring instruments
		2.6 Linear and non-linear devices
		2.7 Ohm’s law
		2.8 Multiples and sub-multiples
		2.9 Conductors and insulators
		2.10 Electrical power and energy
		2.11 Main effects of electric current
		2.12 Fuses
		2.13 Insulation and the dangers of constant high current flow
	Chapter 3. Resistance variation
		3.1 Resistor construction
		3.2 Resistance and resistivity
		3.3 Temperature coefficient of resistance
		3.4 Resistor colour coding and ohmic values
	Chapter 4.
Batteries and alternative sources of energy
		4.1 Introduction to batteries
		4.2 Some chemical effects of electricity
		4.3 The simple cell
		4.4 Corrosion
		4.5 E.m.f. and internal resistance of a cell
		4.6 Primary cells
		4.7 Secondary cells
		4.8 Cell capacity
		4.9 Safe disposal of batteries
		4.10 Fuel cells
		4.11 Alternative and renewable energy sources
	Revision Test 1
	Chapter 5. Series and parallel networks
		5.1 Series circuits
		5.2 Potential divider
		5.3 Parallel networks
		5.4 Current division
		5.5 Loading effect
		5.6 Potentiometers and rheostats
		5.7 Relative and absolute voltages
		5.8 Earth potential and short circuits
		5.9 Wiring lamps in series and in parallel
	Chapter 6. Capacitors and capacitance
		6.1 Introduction to capacitors
		6.2 Electrostatic field
		6.3 Electric field strength
		6.4 Capacitance
		6.5 Capacitors
		6.6 Electric flux density
		6.7 Permittivity
		6.8 The parallel plate capacitor
		6.9 Capacitors connected in parallel and series
		6.10 Dielectric strength
		6.11 Energy stored in capacitors
		6.12 Practical types of capacitor
		6.13 Discharging capacitors
	Chapter 7. Magnetic circuits
		7.1 Introduction to magnetism and magnetic circuits
		7.2 Magnetic fields
		7.3 Magnetic flux and flux density
		7.4 Magnetomotive force and magnetic field strength
		7.5 Permeability and B–H curves
		7.6 Reluctance
		7.7 Composite series magnetic circuits
		7.8 Comparison between electrical and magnetic quantities
		7.9 Hysteresis and hysteresis loss
	Revision Test 2
	Chapter 8. Electromagnetism
		8.1 Magnetic field due to an electric current
		8.2 Electromagnets
		8.3 Force on a current-carrying conductor
		8.4 Principle of operation of a simple d.c. motor
		8.5 Principle of operation of a moving-coil instrument
		8.6 Force on a charge
	Chapter 9. Electromagnetic induction
		9.1 Introduction to electromagnetic induction
		9.2 Laws of electromagnetic induction
		9.3 Rotation of a loop in a magnetic field
		9.4 Inductance
		9.5 Inductors
		9.6 Energy stored
		9.7 Inductance of a coil
		9.8 Mutual inductance
	Chapter 10. Electrical measuring instruments and measurements
		10.1 Introduction
		10.2 Analogue instruments
		10.3 Moving-iron instrument
		10.4 The moving-coil rectifier instrument
		10.5 Comparison of moving-coil, moving-iron and moving-coil rectifier instruments
		10.6 Shunts and multipliers
		10.7 Electronic instruments
		10.8 The ohmmeter
		10.9 Multimeters
		10.10 Wattmeters
		10.11 Instrument ‘loading’ effect
		10.12 The oscilloscope
		10.13 Virtual test and measuring instruments
		10.14 Virtual digital storage oscilloscopes
		10.15 Waveform harmonics
		10.16 Logarithmic ratios
		10.17 Null method of measurement
		10.18 Wheatstone bridge
		10.19 D.C. potentiometer
		10.20 A.C. bridges
		10.21 Q-meter
		10.22 Measurement errors
	Chapter 11.
Semiconductor diodes
		11.1 Types of material
		11.2 Semiconductor materials
		11.3 Conduction in semiconductor materials
		11.4 The p-n junction
		11.5 Forward and reverse bias
		11.6 Semiconductor diodes
		11.7 Characteristics and maximum ratings
		11.8 Rectification
		11.9 Zener diodes
		11.10 Silicon controlled rectifiers
		11.11 Light emitting diodes
		11.12 Varactor diodes
		11.13 Schottky diodes
	Chapter 12. Transistors
		12.1 Transistor classification
		12.2 Bipolar junction transistors (BJT)
		12.3 Transistor action
		12.4 Leakage current
		12.5 Bias and current flow
		12.6 Transistor operating configurations
		12.7 Bipolar transistor characteristics
		12.8 Transistor parameters
		12.9 Current gain
		12.10 Typical BJT characteristics and maximum ratings
		12.11 Field effect transistors
		12.12 Field effect transistor characteristics
		12.13 Typical FET characteristics and maximum ratings
		12.14 Transistor amplifiers
		12.15 Load lines
	Revision Test 3
	Formulae for basic electrical and electronic principles
Section 2: Further Electrical and Electronic Principles
	Chapter 13. D.C. circuit theory
		13.1 Introduction
		13.2 Kirchhoff’s laws
		13.3 The superposition theorem
		13.4 General d.c. circuit theory
		13.5 Thévenin’s theorem
		13.6 Constant-current source
		13.7 Norton’s theorem
		13.8 Thévenin and Norton equivalent networks
		13.9 Maximum power transfer theorem
	Chapter 14. Alternating voltages and currents
		14.1 Introduction
		14.2 The a.c. generator
		14.3 Waveforms
		14.4 A.C. values
		14.5 Electrical safety – insulation and fuses
		14.6 The equation of a sinusoidal waveform
		14.7 Combination of waveforms
		14.8 Rectification
		14.9 Smoothing of the rectified output waveform
	Revision Test 4
	Chapter 15. Single-phase series a.c. circuits
		15.1 Purely resistive a.c. circuit
		15.2 Purely inductive a.c. circuit
		15.3 Purely capacitive a.c. circuit
		15.4 R–L series a.c. circuit
		15.5 R–C series a.c. circuit
		15.6 R–L–C series a.c. circuit
		15.7 Series resonance
		15.8 Q-factor
		15.9 Bandwidth and selectivity
		15.10 Power in a.c. circuits
		15.11 Power triangle and power factor
	Chapter 16. Single-phase parallel a.c. circuits
		16.1 Introduction
		16.2 R–L parallel a.c. circuit
		16.3 R–C parallel a.c. circuit
		16.4 L–C parallel circuit
		16.5 LR–C parallel a.c. circuit
		16.6 Parallel resonance and Q-factor
		16.7 Power factor improvement
	Chapter 17. Filter networks
		17.1 Introduction
		17.2 Two-port networks and characteristic impedance
		17.3 Low-pass filters
		17.4 High-pass filters
		17.5 Band-pass filters
		17.6 Band-stop filters
	Chapter 18. D.C. transients
		18.1 Introduction
		18.2 Charging a capacitor
		18.3 Time constant for a C−R circuit
		18.4 Transient curves for a C−R circuit
		18.5 Discharging a capacitor
		18.6 Camera flash
		18.7 Current growth in an L−R circuit
		18.8 Time constant for an L−R circuit
		18.9 Transient curves for an L−R circuit
		18.10 Current decay in an L−R circuit
		18.11 Switching inductive circuits
		18.12 The effects of time constant on a rectangular waveform
	Chapter 19. Operational amplifiers
		19.1 Introduction to operational amplifiers
		19.2 Some op amp parameters
		19.3 Op amp inverting amplifier
		19.4 Op amp non-inverting amplifier
		19.5 Op amp voltage-follower
		19.6 Op amp summing amplifier
		19.7 Op amp voltage comparator
		19.8 Op amp integrator
		19.9 Op amp differential amplifier
		19.10 Digital to analogue (D/A) conversion
		19.11 Analogue to digital (A/D) conversion
	Revision Test 5
	Formulae for further electrical and electronic principles
Section 3: Electrical Power Technology
	Chapter 20. Three-phase systems
		20.1 Introduction
		20.2 Three-phase supply
		20.3 Star connection
		20.4 Delta connection
		20.5 Power in three-phase systems
		20.6 Measurement of power in three-phase systems
		20.7 Comparison of star and delta connections
		20.8 Advantages of three-phase systems
	Chapter 21. Transformers
		21.1 Introduction
		21.2 Transformer principle of operation
		21.3 Transformer no-load phasor diagram
		21.4 E.m.f. equation of a transformer
		21.5 Transformer on-load phasor diagram
		21.6 Transformer construction
		21.7 Equivalent circuit of a transformer
		21.8 Regulation of a transformer
		21.9 Transformer losses and efficiency
		21.10 Resistance matching
		21.11 Auto transformers
		21.12 Isolating transformers
		21.13 Three-phase transformers
		21.14 Current transformers
		21.15 Voltage transformers
	Revision Test 6
	Chapter 22. D.C. machines
		22.1 Introduction
		22.2 The action of a commutator
		22.3 D.C.machine construction
		22.4 Shunt, series and compound windings
		22.5 E.m.f. generated in an armature winding
		22.6 D.C. generators
		22.7 Types of d.c. generator and their characteristics
		22.8 D.C.machine losses
		22.9 Efficiency of a d.c. generator
		22.10 D.C. motors
		22.11 Torque of a d.c.motor
		22.12 Types of d.c.motor and their characteristics
		22.13 The efficiency of a d.c.motor
		22.14 D.C. motor starter
		22.15 Speed control of d.c.motors
		22.16 Motor cooling
	Chapter 23. Three-phase induction motors
		23.1 Introduction
		23.2 Production of a rotating magnetic field
		23.3 Synchronous speed
		23.4 Construction of a three-phase induction motor
		23.5 Principle of operation of a three-phase induction motor
		23.6 Slip
		23.7 Rotor e.m.f. and frequency
		23.8 Rotor impedance and current
		23.9 Rotor copper loss
		23.10 Induction motor losses and efficiency
		23.11 Torque equation for an induction motor
		23.12 Induction motor torque-speed characteristics
		23.13 Starting methods for induction motors
		23.14 Advantages of squirrel-cage induction motors
		23.15 Advantages of wound rotor induction motors
		23.16 Double cage induction motor
		23.17 Uses of three-phase induction motors
	Revision Test 7
	Formulae for electrical power technology
Section 4: Laboratory Experiments
	Chapter 24. Some practical laboratory experiments
		24.1 Ohm’s law
		24.2 Series-parallel d.c. circuit
		24.3 Superposition theorem
		24.4 Thévenin’s theorem
		24.5 Use of a CRO to measure voltage, frequency and phase
		24.6 Use of a CRO with a bridge rectifier circuit
		24.7 Measurement of the inductance of a coil
		24.8 Series a.c. circuit and resonance
		24.9 Parallel a.c. circuit and resonance
		24.10 Charging and discharging a capacitor
	Answers to multiple-choice questions
Document Text Contents
Page 220


Chapter 14

Alternating voltages
and currents

At the end of this chapter you should be able to:

• appreciate why a.c. is used in preference to d.c.
• describe the principle of operation of an a.c. generator
• distinguish between unidirectional and alternating waveforms
• define cycle, period or periodic time T and frequency f of a waveform
• perform calculations involving T =1/ f
• define instantaneous, peak, mean and r.m.s. values, and form and peak factors for a sine wave
• calculate mean and r.m.s. values and form and peak factors for given waveforms
• understand and perform calculations on the general sinusoidal equation v= Vm sin (ωt ±φ)
• understand lagging and leading angles
• combine two sinusoidal waveforms (a) by plotting graphically, (b) by drawing phasors to scale and (c) by


• understand rectification, and describe methods of obtaining half-wave and full-wave rectification
• appreciate methods of smoothing a rectified output waveform

14.1 Introduction

Electricity is produced by generators at power stations
and then distributed by a vast network of transmission
lines (called the National Grid system) to industry and
for domestic use. It is easier and cheaper to gener-
ate alternating current (a.c.) than direct current (d.c.)
and a.c. is more conveniently distributed than d.c.
since its voltage can be readily altered using trans-
formers. Whenever d.c. is needed in preference to a.c.,
devices called rectifiers are used for conversion (see
Section 14.7).

14.2 The a.c. generator

Let a single turn coil be free to rotate at constant angular
velocity symmetrically between the poles of a magnet
system as shown in Fig. 14.1.

An e.m.f. is generated in the coil (from Faraday’s
laws) which varies in magnitude and reverses its direc-
tion at regular intervals. The reason for this is shown
in Fig. 14.2. In positions (a), (e) and (i) the conductors
of the loop are effectively moving along the magnetic
field, no flux is cut and hence no e.m.f. is induced. In
position (c) maximum flux is cut and hence maximum
e.m.f. is induced. In position (g), maximum flux is cut

DOI: 10.1016/B978-0-08-089056-2.00014-0

Page 221





210 Electrical and Electronic Principles and Technology

Figure 14.1

Figure 14.2

and hence maximum e.m.f. is again induced. However,
using Fleming’s right-hand rule, the induced e.m.f. is in
the opposite direction to that in position (c) and is thus
shown as −E . In positions (b), (d), (f) and (h) some
flux is cut and hence some e.m.f. is induced. If all such

Figure 14.3

positions of the coil are considered, in one revolution
of the coil, one cycle of alternating e.m.f. is produced
as shown. This is the principle of operation of the a.c.
generator (i.e. the alternator).

14.3 Waveforms

If values of quantities which vary with time t are plotted
to a base of time, the resulting graph is called a wave-
form. Some typical waveforms are shown in Fig. 14.3.
Waveforms (a) and (b) are unidirectional waveforms,
for, although they vary considerably with time, they flow
in one direction only (i.e. they do not cross the time axis
and become negative). Waveforms (c) to (g) are called
alternating waveforms since their quantities are con-
tinually changing in direction (i.e. alternately positive
and negative).
A waveform of the type shown in Fig. 14.3(g) is called
a sine wave. It is the shape of the waveform of e.m.f.
produced by an alternator and thus the mains electricity
supply is of ‘sinusoidal’ form.
One complete series of values is called a cycle (i.e. from
O to P in Fig. 14.3(g)).
The time taken for an alternating quantity to complete
one cycle is called the period or the periodic time, T,
of the waveform.
The number of cycles completed in one second is called
the frequency, f, of the supply and is measured in hertz,
Hz. The standard frequency of the electricity supply in
Great Britain is 50 Hz

T = 1

or f = 1

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