Electrical Engineering: Know It All

by Clive Maxfield, CEng Bird BSc (Hons), Tim Williams, Walt Kester, Dan Bensky

Overview

The Newnes Know It All Series takes the best of what our authors have written to create hard-working desk references that will be an engineer's first port of call for key information, design techniques and rules of thumb. Guaranteed not to gather dust on a shelf! Electrical engineers need to master a wide area of topics to excel. The Electrical Engineering Know It All covers every angle including Real-World Signals and Systems, Electromagnetics, and Power systems. - A 360-degree view from our best-selling authors - Topics include digital, analog, and power electronics, and electric circuits - The ultimate hard-working desk reference; all the essential information, techniques and tricks of the trade in one volume

Product Details

ISBN-13:	9780080949666
Publisher:	Butterworth-Heinemann
Publication date:	04/19/2011
Series:	Newnes Know It All
Sold by:	Barnes & Noble
Format:	eBook
Pages:	1128
File size:	19 MB
Note:	This product may take a few minutes to download.

About the Author

Clive "Max" Maxfield received a BS in Control Engineering from Sheffield Polytechnic, England in 1980. He began his career as a mainframe CPU designer for International Computers Limited (ICL) in Manchester, England. Max now finds himself a member of the technical staff (MTS) at Intergraph Electronics, Huntsville, Alabama. Max is the author of dozens of articles and papers appearing in magazines and at technical conferences around the world. Max's main area of interest are currently focused in the analog, digital, and mixed-signal simulation of integrated circuits and multichip modules.John Bird, the author of over 100 textbooks on engineering and mathematical subjects, is the former Head of Applied Electronics in the Faculty of Technology at Highbury College, Portsmouth, U.K. More recently, he has combined freelance lecturing at Portsmouth University, with technical writing and Chief Examiner responsibilities for City and Guilds Telecommunication Principles and Mathematics, and examining for the International Baccalaureate Organisation. John Bird is currently a Senior Training Provider at the Royal Naval School of Marine Engineering in the Defence College of Marine and Air Engineering at H.M.S. Sultan, Gosport, Hampshire, U.K. The school, which serves the Royal Navy, is one of Europe's largest engineering training establishments.Tim Williams worked for a variety of companies as an electronic design engineer, before startinghis own consultancy specializing in EMC design and test advice and training. He has monitored the progress of the EMC Directive and its associated standards since it was first made public, over the last 25 years.Alan Bensky, MScEE, an electronics engineering consultant with over 25 years of experience in analog and digital design, management, and marketing. Specializing in wireless circuits and systems, Bensky has carried out projects for varied military and consumer applications. He is the author of Short-range Wireless Communication, Second Edition, published by Elsevier, 2004, and has written several articles in international and local publications. He has taught courses and gives lectures on radio engineering topics. Bensky is a senior member of IEEE.
John Bird, the author of over 100 textbooks on engineering and mathematical subjects, is the former Head of Applied Electronics in the Faculty of Technology at Highbury College, Portsmouth, U.K. More recently, he has combined freelance lecturing at Portsmouth University, with technical writing and Chief Examiner responsibilities for City and Guilds Telecommunication Principles and Mathematics, and examining for the International Baccalaureate Organisation. John Bird is currently a Senior Training Provider at the Royal Naval School of Marine Engineering in the Defence College of Marine and Air Engineering at H.M.S. Sultan, Gosport, Hampshire, U.K. The school, which serves the Royal Navy, is one of Europe’s largest engineering training establishments.

Read an Excerpt

Electrical Engineering

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By Clive Maxfield John Bird M. A. Laughton W. Bolton Andrew Leven Ron Schmitt Keith Sueker Tim Williams Mike Tooley Luis Moura Izzat Darwazeh Walt Kester Alan Bensky DF Warne

Newnes

Copyright © 2008 Elsevier Inc.
All right reserved.
ISBN: 978-0-08-094966-6

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Chapter One

An Introduction to Electric Circuits John Bird

1.1 SI Units

The system of units used in engineering and science is the Système International d'Unités (International system of units), usually abbreviated to SI units, and is based on the metric system. This was introduced in 1960 and is now adopted by the majority of countries as the official system of measurement.

The basic units in the SI system are listed with their symbols, in Table 1.1.

Derived SI units use combinations of basic units and there are many of them. Two examples are:

• Velocity—meters per second (m/s)

• Acceleration—meters per second squared (m/s²)

SI units may be made larger or smaller by using prefixes that denote multiplication or division by a particular amount. The six most common multiples, with their meaning, are listed in Table 1.2.

1.2 Charge

The unit of charge is the coulomb (C) where one coulomb is one ampere second. (1 coulomb = 6.24 × 10¹⁸ electrons). The coulomb is defined as the quantity of electricity that flows past a given point in an electric circuit when a current of one ampere is maintained for one second. Thus,

charge, in coulombs Q = It

where I is the current in amperes and t is the time in seconds.

Example 1.1

If a current of 5A flows for 2 minutes, find the quantity of electricity transferred.

Solution

Quantity of electricity Q It coulombs

I = 5 A, t = 2 × 60 = 120s

Hence, Q = 5 × 120 = 600C

1.3 Force

The unit of force is the newton (N) where one newton is one kilogram meter per second squared. The newton is defined as the force which, when applied to a mass of one kilogram, gives it an acceleration of one meter per second squared. Thus,

force, in newtons F = ma

where m is the mass in kilograms and a is the acceleration in meters per second squared. Gravitational force, or weight, is mg, where g = 9.81m/s2.

Example 1.2

A mass of 5000g is accelerated at 2m/s² by a force. Determine the force needed.

Solution

Force = mass × acceleration

= 5 kg × m/s² kg m/s² = 10N

Example 1.3

Find the force acting vertically downwards on a mass of 200g attached to a wire.

Solution

Mass = 200g = 0.2kg and acceleration due to gravity, g = 9.81m/s²

Force acting downwards = weight = mass × acceleration

= 0.2 kg × 9.81 mm/s²

= 1.962 N

1.4 Work

The unit of work or energy is the joule (J) where one joule is one Newton meter. The joule is defined as the work done or energy transferred when a force of one newton is exerted through a distance of one meter in the direction of the force. Thus,

work done on a body, in joules W = Fs

where F is the force in Newtons and s is the distance in meters moved by the body in the direction of the force. Energy is the capacity for doing work.

1.5 Power

The unit of power is the watt (W) where one watt is one joule per second. Power is defined as the rate of doing work or transferring energy. Thus,

power in watts, P = W/t

where W is the work done or energy transferred in joules and t is the time in seconds. Thus, energy, in joules, W = Pt

Example 1.4

A portable machine requires a force of 200N to move it. How much work is done if the machine is moved 20m and what average power is utilized if the movement takes 25s?

Solution

Work done = force × distance = 200N × 20m = 4000Nm or 4kJ

Power = work done/time taken

= 4000 J/25s = 160 J/s = 160 W

Example 1.5

A mass of 1000kg is raised through a height of 10m in 20s. What is (a) the work done and (b) the power developed?

Solution

(a) Work done = force × distance and force = mass × acceleration Hence, work done = (1000 kg × 9.81 m/s2) × (10 m) = 98 100 Nm = 98.1 kNm or 988.1 kJ

(b) Power = work done/time taken = 98 100 J/20 s = 4905 J/s = 4905 W or 4.905 kW

1.6 Electrical Potential and e.m.f.

The unit of electric potential is the volt (V) where one volt is one joule per coulomb. One volt is defined as the difference in potential between two points in a conductor which, when carrying a current of one ampere, dissipates a power of one watt, i.e.,

volts = watts/amperes = joules/second/amperes = joules/ampere second = joules/coulombs

A change in electric potential between two points in an electric circuit is called a potential difference. The electromotive force (e.m.f.) provided by a source of energy such as a battery or a generator is measured in volts.

1.7 Resistance and Conductance

The unit of electric resistance is the ohm (ω) where one ohm is one volt per ampere. It is defined as the resistance between two points in a conductor when a constant electric potential of one volt applied at the two points produces a current flow of one ampere in the conductor. Thus,

resistance, in ohms R = V/I

where V is the potential difference across the two points in volts and I is the current flowing between the two points in amperes.

The reciprocal of resistance is called conductance and is measured in siemens (S). Thus, conductance, in siemens G = 1/R

where R is the resistance in ohms.

Example 1.6

Find the conductance of a conductor of resistance (a) 10, (b) 5k and (c) 100m.

Solution

(a) Conductance G = 1/R = 1/10 siemen = 0.1S

(b) G = 1/R = 1/5 × 10³ S = 0.2 × 10^-3 S = 0.2 mS

(c) G = 1/R = 1/5 × 10³ S = 10³/100 S = 10S

1.8 Electrical Power and Energy

When a direct current of I amperes is flowing in an electric circuit and the voltage across the circuit is V volts, then,

power, in watts P = VI

Electrical energy = Power time × time

= VIt joules

Although the unit of energy is the joule, when dealing with large amounts of energy, the unit used is the kilowatt hour (kWh) where

1kWh = 1000 watt hour = 1000 × 3600 watt seconds or joules = 3,600,000 J

Example 1.7

A source e.m.f. of 5V supplies a current of 3A for 10 minutes. How much energy is provided in this time?

Solution

Energy = power × time and power = voltage × current. Hence, Energy = VIt = 5 × 3 × (10 × 60) = 9000 Ws or J = 9kJ

Example 1.8

An electric heater consumes 1.8MJ when connected to a 250V supply for 30 minutes. Find the power rating of the heater and the current taken from the supply.

Solution

Energy = power × time, power = energy/time = 1.8 × 10⁶ J/30 × 60s = 1000 J/s = 1000 W

i.e., Power rating of heater 1kW

Power thus, P = VI, thus, I = P/V = 1000/250 = 4 A

Hence, the current taken from the supply is 4 A.

1.9 Summary of Terms, Units and Their Symbols

1.10 Standard Symbols for Electrical Components

Symbols are used for components in electrical circuit diagrams and some of the more common ones are shown in Figure 1.1.

1.11 Electric Current and Quantity of Electricity

All atoms consist of protons, neutrons and electrons. The protons, which have positive electrical charges, and the neutrons, which have no electrical charge, are contained within the nucleus. Removed from the nucleus are minute negatively charged particles called electrons. Atoms of different materials differ from one another by having different numbers of protons, neutrons and electrons. An equal number of protons and electrons exist within an atom and it is said to be electrically balanced, as the positive and negative charges cancel each other out. When there are more than two electrons in an atom the electrons are arranged into shells at various distances from the nucleus.

All atoms are bound together by powerful forces of attraction existing between the nucleus and its electrons. Electrons in the outer shell of an atom, however, are attracted to their nucleus less powerfully than are electrons whose shells are nearer the nucleus.

It is possible for an atom to lose an electron; the atom, which is now called an ion, is not now electrically balanced, but is positively charged and is thus able to attract an electron to itself from another atom. Electrons that move from one atom to another are called free electrons and such random motion can continue indefinitely. However, if an electric pressure or voltage is applied across any material there is a tendency for electrons to move in a particular direction. This movement of free electrons, known as drift, constitutes an electric current flow. Thus current is the rate of movement of charge.

Conductors are materials that contain electrons that are loosely connected to the nucleus and can easily move through the material from one atom to another.

Insulators are materials whose electrons are held firmly to their nucleus.

The unit used to measure the quantity of electrical charge Q is called the coulomb C (where 1 coulomb = 6.24 × 10¹⁸ electrons).

If the drift of electrons in a conductor takes place at the rate of one coulomb per second the resulting current is said to be a current of one ampere.

Thus, 1 ampere = 1 coulomb per second or 1A = 1C/s. Hence, 1 coulomb = 1 ampere second or 1 C = 1 As. Generally, if I is the current in amperes and t the time in seconds during which the current flows, then I × t represents the quantity of electrical charge in coulombs, i.e., quantity of electrical charge transferred,

Q = I × t coulombs

Example 1.9

What current must flow if 0.24 coulombs is to be transferred in 15ms?

Solution

Since the quantity of electricity, Q It, then

I = Q/t = 0.24/15 × 10-3 = 0.24 × 10³/15 = 240/15 = 16 A

Example 1.10

If a current of 10A flows for 4 minutes, find the quantity of electricity transferred.

Solution

Quantity of electricity, Q = It coulombs

I = 10 A; t = 4 × 60 = 240s Hence, Q = 10 × 240 = 2400C

1.12 Potential Difference and Resistance

For a continuous current to flow between two points in a circuit a potential difference or voltage, V, is required between them; a complete conducting path is necessary to and from the source of electrical energy. The unit of voltage is the volt, V.

Figure 1.2 shows a cell connected across a filament lamp. Current flow, by convention, is considered as flowing from the positive terminal of the cell, around the circuit to the negative terminal.

The flow of electric current is subject to friction. This friction, or opposition, is called resistance R and is the property of a conductor that limits current. The unit of resistance is the ohm; 1 ohm is defined as the resistance which will have a current of 1 ampere flowing through it when 1 volt is connected across it, i.e.,

resistance R = potential difference/current

1.13 Basic Electrical Measuring Instruments

An ammeter is an instrument used to measure current and must be connected in series with the circuit. Figure 1.2 shows an ammeter connected in series with the lamp to measure the current flowing through it. Since all the current in the circuit passes through the ammeter it must have a very low resistance.

(Continues...)

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Excerpted from Electrical Engineering by Clive Maxfield John Bird M. A. Laughton W. Bolton Andrew Leven Ron Schmitt Keith Sueker Tim Williams Mike Tooley Luis Moura Izzat Darwazeh Walt Kester Alan Bensky DF Warne Copyright © 2008 by Elsevier Inc.. Excerpted by permission of Newnes. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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Table of Contents

Chapter 1 An Introduction to Electric CircuitsChapter 2 Resistance and ResistivityChapter 3 Series and parallel networksChapter 4 Capacitors and InductorsChapter 5 D.c. circuit theoryChapter 6 Alternating voltages and currentsChapter 7 Complex NumbersChapter 8 Transients and Laplace transformsChapter 9 Frequency Domain Circuit AnalysisChapter 10 Digital ElectronincsChapter 11 Analog ElectronicsChapter 12 Circuit simulationChapter 13 InterfacingChapter 14 Microcontrollers and MicroprocessorsChapter 15 Power ElectronicsChapter 16 Signals and Signal ProcessingChapter 17 Filter DesignChapter 18 Control and Instrumentation SystemsChapter 19 Communications SystemsChapter 20 Principles of ElectromagneticsChapter 21 MAGNETIC FIELDSChapter 22 Electromagnetic Transients and EMIChapter 23 Traveling Wave EffectsChapter 24 TransformersChapter 25 Electromagnetic MachinesChapter 26 Electromagnetic Compatibility (EMC)Chapter 27 Power GenerationChapter 28 Power Transmission and DistributionChapter 29 Power QualityAppendix A General referenceAppendix B Differential Equations

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