An Introduction to Electrical Science

Adrian Waygood

• Publisher: Routledge
• Year: 2018
• eBook ISBN: 9781351190411
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Heavily updated and expanded, this second edition of Adrian Waygood's textbook provides an indispensable introduction to the science behind electrical engineering.

While fully matched to the electrical science requirements of the 2330 levels 2 and 3 Certificates in Electrotechnical Technology from City & Guilds (Electrical Installation), the main purpose of this book is to develop an easy understanding of the how and why within each topic. It is aimed at those starting careers in electricity and electronics, as well as any hobbyists, with an array of new material to reflect changes in the industry.

New chapters include:

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• Electrical drawings

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• Practical resistors

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• Measuring instruments

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• Basic motor action

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• Practical capacitors

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• Basic transformer theory

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• The electricity supply industry

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• …and more

The author details the historical context of each main principle and offers a wealth of examples, images and diagrams, all whilst maintaining his signature conversational and accessible style. There is also a companion website, with interactive multiple choice quizzes for each chapter and more, at www.routledge.com/cw/waygood

Chapter 1
SI system of measurements

Objectives

On completion of this chapter, you should be able to

1. explain the term ‘SI base units’.
2. list the seven SI base units.
3. explain the term ‘SI derived units’.
4. explain the relationship between SI ‘base’ and ‘derived’ units.
5. recognise SI prefixes.
6. apply correct SI symbols.
7. use correct SI prefixes.
8. apply SI conventions when writing SI units.
9. be aware of changes to SI base units scheduled for 2019.

Introduction

In 1948, the General Conference of Weights and Measures (CGPM) charged an international committee, the CIPM*, to ‘study the establishment of a complete set of rules for (metric) units of measurement’.

*CIPM (Comité international des poid et mesures) is an International Committee for Weights and Measurements comprising eighteen individuals, each from a different member state, whose principal task is to promote world-wide uniformity in units of measurement. The Committee achieves this either by direct action, or by submitting proposals to the General Conference on Weights and Measures.

The outcome of this study was a rational system of metric units termed ‘SI’.

The abbreviation SI stands for Système Internationale d’Unités and this system of measurements has been adopted internationally by the scientific and engineering communities, as well as by businesses for the purpose of international trade. Whereas most countries now use SI exclusively, some countries – most notably the United States and, to a lesser extent, the United Kingdom – still make wide use of non-metric units, especially for day-to-day use.

Earlier versions of the metric system include the ‘cgsA’ (‘centimetre, gram, second, ampere’) and the ‘mksA’ (‘metre, kilogram, second, ampere’) systems. SI is largely based on the ‘mksA’ system.

SI comprises two classes of units:

• base units
• derived units.

Base units

There are seven base units from which all other SI units are derived. These are shown in Table 1.1.

Table 1.1

Quantity	SI unit	SI symbol
length	metre	m
mass*	kilogram	kg
time	second	s
electric current	ampere	A
temperature	kelvin	K
luminous intensity	candela	cd
amount of substance	mole	mol

* The kilogram is a little confusing because it is the only base unit with a prefix (kilo). It has been suggested that the name ‘kilogram’ should be replaced (to remove the prefix ‘kilo’) as the unit for mass, but this is likely to cause more confusion than n...

Table of contents

• Cover
• Title
• Copyright
• Dedication
• Contents
• Foreword
• Introduction
• 1 SI system of measurements
• 2 Electrical schematic and wiring diagrams
• 3 The 'electron theory' of electricity
• 4 Electric current
• 5 Potential and potential difference
• 6 Resistance
• 7 Resistors
• 8 Conductors and cables
• 9 Effect of temperature change upon resistance
• 10 Ohm's Law of constant proportionality
• 11 Series, parallel and series-parallel circuits
• 12 Electrical measurements
• 13 Cells and batteries
• 14 Internal resistance
• 15 Energy, work, heat and power
• 16 Magnetism
• 17 Electromagnetism
• 18 Magnetic circuits
• 19 Electromagnetic induction
• 20 Motor principle
• 21 Transformers
• 22 Capacitance
• 23 Capacitors
• 24 Geometry and trigonometry revision for a.c.
• 25 Introduction to alternating current
• 26 Series alternating-current circuits
• 27 Power in alternating-current circuits
• 28 Parallel alternating-current circuits
• 29 Summary of equations derived from phasor diagrams
• 30 Power factor improvement
• 31 Balanced three-phase a.c. systems