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ISBN: 978-0170192743
For learning solutions, visit cengage.com.au
9 780170 192743
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Brief contents
Chapter 1 The electric circuit
Chapter 2 Voltage sources and effects of an electric current
Chapter 3 Ohm’s law
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Prefacexvi
Resources guide
xvii
Acknowledgementsxx
About the author
xxi
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Brief contents
v
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Chapter 5 Resistance and resistors
Chapter 6 The series circuit
Chapter 7 The parallel circuit
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Chapter 4 Electrical power
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Chapter 8 The series–parallel circuit
143
Chapter 9 Basic meters
157
Chapter 10 Capacitance 188
Chapter 11 Magnetism and electromagnets
220
Chapter 12 Electromagnetic induction
251
Chapter 13 DC generators
269
Chapter 14 DC motors
299
Chapter 15 AC fundamentals
331
358
Chapter 17 Series combinations of R, L and C
377
Chapter 18 Parallel AC circuits 400
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Chapter 16 Pure R, L or C in an AC circuit
Chapter 19 Single-phase power
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Chapter 20 Three-phase power
418
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Chapter 21 Transformers474
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Chapter 23 Single-phase motors
555
Chapter 24 Synchronous machines
569
Chapter 25 Test equipment and batteries
594
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Chapter 22 Three-phase motors
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Appendix637
Solutions640
Index656
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27
CHAPTER 2 Voltage sources and effects of an electric current
FIGURE 2.4
Piezo-electric effect,
where pressure is
applied to opposite
faces of a quartz crystal
to produce a voltage.
Pressure can be by
compressing, flexing
or distorting the piezo
element.
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The piezo-electric effect was discovered in 1880 by the Curie brothers. (Piezo is Greek for pressure.)
They found that when mechanical stress was applied to crystals such as topaz, quartz, Rochelle
salt and cane sugar, electrical charges appeared, and that this voltage was proportional to the
applied stress. Materials that have this characteristic are called piezo-electric materials.
The piezo-electric effect occurs when the charge balance within the crystal lattice of a piezo
material is disturbed. When there is no applied stress on the material, the positive and negative
charges are evenly distributed so there is no potential difference. When the lattice is changed
slightly, the charge imbalance creates a potential difference, often as high as several thousand
volts. However, the current is extremely small and only causes a small electric shock.
Piezo elements are used in electronic cigarette lighters, gas lighters, guitar pick-ups, some
kinds of microphones and various types of sensors, such as accelerometers. When used in
electronic gas lighters, a trigger-operated mechanical mechanism is arranged to apply a short,
sharp force to the piezeo element, which produces a voltage that is high enough to cause a
spark, as in Figure 2.4. In a microphone, the variations in air pressure due to sound waves
cause the piezo-electric crystal element in the microphone to produce a very small voltage that
changes with the sound waves.
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Piezo-electric crystal
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Magnetism
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Magnetism plays a big role in the electrotechnology
industry, and the topics of magnetism and
electromagnetism are covered in Chapters 11
and 12. In principle, if a conductor is moved
through a magnetic field, a voltage is induced
in the conductor. This effect was discovered by
Michael Faraday in 1831, a discovery that led to
the electrical power generation industry of today.
Figure 2.5 shows a single conductor being moved
through a magnetic field, although the voltage it
produces will be very small (a few millionths of
a volt).
Faraday found that the faster the conductor
moves through a magnetic field, the higher the
voltage. It doesn’t matter whether the magnetic
field or the conductor moves – a voltage is produced
if either moves relative to the other. He also found
02_Electrical Principles 2ed SB 9780170192743 TXT.indd 27
FIGURE 2.5
Producing a voltage
by using mechanical
energy to move a
conductor in a magnetic
field
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