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I

SCHAUM’S OUTLZNE OF

THEORY AND PROBLEMS
OF

BASIC ELECTRICITY

MILTON GUSSOW, M.S.
Senior Engineer
Applied Physics Laboratory
The Johns Hopkins University

McGraw-Hill
New York San

Tokyo Toronto

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.

-

w

To Libbie, Myra, and Susan

MILTON GUSSOW is a senior
Naval

at Johns
B.S. (1949) from the U.S.

his B.S.E.E. (1956) from
(1957) from
in mathematics

elkctrical engineering. Mr. Gussow was
of over fifty technical
Schaum’s Outline of Theory and Problems of
BASIC ELECTRICITY
Copyright 0 1983 by The McGraw-Hill Companies, Inc.
of America.
as permitted
be reproduced or distributed in any form or by any
of the
system,

or stored in a data base or retrieval

16 17 18 19 20 BAW 9

I S B N 0-03-025240-8
Sponsoring Editor, John Aliano
Consulting Editor, Gordon Rockmaker

Editing Supervisor, Marthe Grice
Production Manager, Nick Monti

Library of Congress Catalogjng in Publication Data

Gussow, Milton.
Schaum’s outline of theory and problems of basic
electricity.
(Schaum’s
1 . Electricity. I. Title.
TK146.G974 1983
62 1.3‘02‘02
ISBN 0-07-025240-8

McGraw-Hill

82-467 1

E

A Division of 7-kMc#uw.Ha Companies

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Preface

This book is intended as a basic text to cover the fundamentals of electricity
and electric circuits. It may be used by beginning students in
schools,

technical institutes, and colleges who have no experience in electricity.
Explanations and step-by-step solutions are deliberately detailed so that the
text can stand alone. Thus it also may be used as a home-study or reference
book. A knowledge of basic algebra and trigonometry is assumed. Designed to
provide a broad and deep background in the nature of electricity and the operation and application of electric circuits, the text uses numerous and easy-tofollow examples accompanied by diagrams. Starting with the physics of electric
current flow, the book describes and analyzes both direct-current and alternating-current electric circuits, generators and motors, transformers, and measuring
instruments. To assure correlation to modern practice and design, illustrative
problems are presented in terms of commonly used voltages and current ratings,
covering circuits and equipments typical of those found in today’s electrical
systems.
There are several special features of this book. One is the use of the
International System of Units (SI) throughout. A second is the prolific use of
equation numbers for reference so that the reader will always know the source of
each equation used. Other features include simplified ways to solve problems on
three-phase transformer windings, series and parallel resonance, and RL and RC
circuit waveforms.
I wish to thank John Aliano, Gordon Rockmaker, and Marthe Grice of the
McGraw-Hill Book Company for their many constructive criticisms and continuing efforts to get this book published.
MILTON Gussow

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Contents


Chapter

1

THE NATURE OF ELECTRICITY

.................................

Structure of the Atom ...................................................
The Electric Charge .....................................................
The Coulomb ...........................................................
The Electrostatic Field ...................................................
Potential Difference .....................................................
Current ................................................................
Current Flow ...........................................................
Sources of Electricity ....................................................
Direct
..............................

Chapter

2

ELECTRICAL

AND CONVENTIONS

..................

Units

Introduction ............................................................
Metric Prefixes ..........................................................
Powers of 10 ...........................................................
Scientific Notation .......................................................
Rounding Off Numbers ..................................................
Graphical Symbols and Electrical Diagrams
Schematic Diagram ......................................................
One-Line Diagram .......................................................
Block
..........................................................
Wiring
.........................................................
Electric Plan ............................................................

Chapter

3

OHM’S LAW AND

.......................................

The Electric Circuit .....................................................
Resistance ..............................................................
Fixed Resistors .........................................................
Variable Resistors .......................................................
Ohm’s Law .............................................................
Electric Power ..........................................................
Horsepower ............................................................
Electrical Energy ........................................................


Chapter

4

DIRECT-CURRENT

............................

Voltage. Current. and Resistance in Series Circuits ..........................
Polarity of Voltage Drops ................................................
Conductors .............................................................
Total Power in a Series Circuit ...........................................
Voltage Drop by Proportional Parts .......................................

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1
1

3
4
4
5
5

6
7
8
15

15
15
16
20
20
27
28
31
31
31

38
38
39
39
40
41
42
43
44

50
50
53
53
57
58


CONTENTS


Chapter

Chapter

5

6

DIRECT-CURRENT

CIRCUITS

........................

Voltage and
in a Parallel
...................................
Resistances in Parallel ...................................................
Open and Short
.................................................
Division of Current in Two
..............................
Conductances in Parallel .................................................
Power in Parallel
................................................

69
71
74

75
75
77

.....................................................

88

BATTERIES

The Voltaic Cell .........................................................
Series
.................................................
Primary
.............................................
Types of Batteries .......................................................
Battery
...................................................

Chapter

7

KIRCHHOFF’S LAWS

............................................

Kirchhoff’s Voltage Law (KVL) ..........................................
Kirchhoff’s Current Law (KCL) ..........................................
Mesh Currents ..........................................................

Node
..........................................................

Chapter

8

NETWORK CALCULATIONS

.....................................

Y and
...................................................
Superposition ...........................................................
Thevenin’s
.....................................................
Norton’s
.......................................................
Series-Parallel
...................................................
Wheatstone Bridge Circuit ...............................................
Maximum Power Transfer ................................................
Line-Drop
..................................................
Three-Wire
..........................................

Chapter

69


........................

9 MAGNETISM

The Nature of Magnetism ................................................
Magnetic Materials ......................................................
Electromagnetism .......................................................
Magnetic Units ..........................................................
BH Magnetization
................................................
Magnetic Circuits .......................................................
Electromagnetic
................................................
International
of Units .............................................

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88
89

90
90
94

101
101
103


104
106

116
116
120
122
124
126
128
129
130
131

162
162
163

164
167

168
170
172
174


CONTENTS

Chapter


10

.................

DIRECT-CURRENT

Motors
..................................................
Simple DC Generator ....................................................
Armature Windings ......................................................
Field Excitation ........................................................
DC Generator
..........................................
Generator Voltage Equations and Voltage Regulation .......................
Losses and Efficiency of a DC Machine ...................................
Direct-Current Motor ....................................................
DC Motor Equivalent
.............................................
Speed of a Motor .......................................................
Motor Types ............................................................
Starting
for Motors .........................................

Chapter

Chapter

Chapter


11

12

13

PRINCIPLES OF ALTERNATING CURRENT

.......................

184
184
185
186
187
188
189
189
191

192
193
194
1%

205

Generating
.........................................
Angular Measurement ...................................................

Sine Wave ..............................................................
Alternating
......................................................
Frequency
...................................................
Phase Relationships .....................................................
Phasors ................................................................
Characteristic Values of Voltage and Current ...............................
Resistance in AC Circuits ................................................

205
206
207
208
209
209
211
213

INDUCTANCE.
AND INDUCTIVE
CIRCUITS
Induction ...............................................................
Characteristics of Coils ..................................................
Inductive
.....................................................
Inductors in Series or Parallel ............................................
Inductive
.......................................................
Q of a Coil .............................................................

Power in RL Circuits ....................................................

225
225
226
227
228
231
237
237

.......................................................

205

CAPACITANCE.

.......................................................

Capacitor ...............................................................
Capacitance ............................................................
Types of Capacitors .....................................................
Capacitors in Series
..........................................
Capacitive
....................................................
Capacitive
......................................................
Power in RC Circuits ....................................................


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251
251
252
254
254
256
257
262


CONTENTS

Chapter

Chapter

14

15

Chapter

Chapter

16

17


.......................................

SINGLE-PHASE CIRCUITS
The General RLC Circuit ................................................
RLC in Series ..........................................................
RLC in Parallel .........................................................
R L and RC Branches in Parallel ..........................................
Power
.................................................

...........

ALTERNATING-CURRENT GENERATORS AND MOTORS
Alternators ..............................................................
Paralleling
....................................................
Ratings .................................................................
Losses and Efficiency ....................................................
Polyphase
...............................................
Synchronous
.....................................................
Single-Phase Motors .....................................................

................................................

TRANSFORMERS
Ideal Transformer Characteristics .........................................
Transformer
......................................................

Impedance
........................................................
Autotransformer ........................................................
Transformer
and Efficiency ........................................
No-Load
......................................................
Coil Polarity ............................................................

........................................

THREE-PHASE SYSTEMS
Characteristics of Three-Phase
...................................
Three-Phase
....................................
Power in Balanced Three-Phase
....................................
Unbalanced
...........................................

............................

Chapter

16

SERIES AND PARALLEL RESONANCE
Series Resonance .................................................
Q of Series Circuit ................................................

Parallel Resonance ................................................
Q of Parallel Circuit ..............................................
Bandwidth and Power of Resonant Circuit ..........................

Chapter

19

WAVEFORMS AND TIME CONSTANTS
RL Series
............................................
RL Time
......................................................
RC Series
............................................
RC Time Constants .....................................................
Calculation
Time r ...................................................

...........................

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275
275
275
278
280
282


300
300
302
303
303
303
306
310

322
322
325
326
326
327
328
329

339
339
340
342
346

362
362
365
366
369
370


384
384
388
390
393
394


CONTENTS

Chapter 20 ELECTRICAL MEASUREMENTS

..................................

Basic Measuring Instruments .............................................
Ammeters ..............................................................
Voltmeters .............................................................
Ohmmeters .............................................................
Multimeters .............................................................
Alternating-Current Meters ...............................................
Wattmeters and Watthour Meters .........................................
Analog Electronic Meters ................................................
Digital Meters ...........................................................

INDEX

..........................................................

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411
411
411
414
416
419
419
425
427
429

447


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Chapter 1
The Nature of Electricity
STRUCTURE OF THE ATOM

Matter is

that has
atoms. All matter
compounds. In an element, all the atoms are the same.
copper, carbon, germanium,


elements or
of elements are aluminum,

molecule.
Atoms are composed of subatomic
of electrons, protons, and neutrons in various
(-) of electricity. Electrons
combinations. The electron is the fundamental
in paths of concentric “shells,” or orbits (Fig.
revolve about the nucleus or center of the
(+) charge of electricity. Protons are found in the
1-1). The proton is the fundamental
nucleus. The number of protons within the
of any particular
14 protons in its nucleus so the
number of silicon is 14. The neutron, which is the fundamental

Nucleus

Electrons

Fig. 1-1 Electrons
an atom

of

Atoms of different
1-2). In its
state, an atom of any element

an equal
of
electrons and
(-) charge of each electron is equal in magnitude to the
positive (+) charge of each proton, the two opposite
1-2).
Example 1.1 Describe the two
1 proton in its nucleus

orbiting
(Fig. 1-2a). The
balanced by 2 electrons

by 1 electron
2 protons in its

1-2b).

has a certain amount of energy, which is equal to the sum of the
A stable
energies of its electrons. Electrons, in turn, have
energy levels. The
energy
of an
is proportional to its distance from the nucleus. Therefore, the energy
levels of electrons in shells farther from the nucleus are higher than those of electrons in shells
1

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2

THE NATURE OF ELECTRICITY

[CHAP. 1

Nucleus

Number of orbiting electrons

1

I/

(2 Protons, 2 Neutrons)

/ Orbiting electron

/

/

/

@
;
;
;
:

:
;
)

/

/

I

I

I
\

\

\

\

/

/

\
/

‘-/
/


(6)Helium atom, 2 orbiting electrons

(a) Hydrogen atom, 1 orbiting electron

Second shell
Second shell

I

I.

Third shell

\

/

I
/
/

Nucleus
(14 protons, 14 neutrons)

(d)Copper atom, 29 orbiting electrons

(c) Silicon atom, 14 orbiting electrons

Fig. 1-2 Atomic structure of four common elements


nearer
external energy

as heat, light, or electric

valence electrons. When
is applied to certain

excited state. An atom in an
state is unstable.
When an electron
moved to the outermost shell of its atom, it is least attracted by the
positive
of the protons within the
of its
If enough
is then
to
will leave
the atom, some of the outermost shell or valence
free electrons. It is the
of free electrons that provides
current in a
metal conductor.
of an
can contain
a certain maximum number of electrons.
Each
quota of a shell.

K,L, M,
is called
N, 0, P, and Q at increasing
filled with 2 electrons, the L
1-3). After
K shell

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3

THE NATURE OF ELECTRICITY

CHAP. I]

0
N

M

K
or
32
Nucleus

Fig. 1-3 Energy

shell
take up to 8 electrons.

8, 18, or 32 for different

maximum number of electrons in the remaining shells can be
8.

Example 1.2 Structure the copper
by identifying its energy
(Fig. 1-2d).
In the copper
there are 29 protons in the
29 orbiting
electrons fill the K shell with 2 electrons
8 electrons. The remaining 19 electrons
18 electrons, and
1 electron in the
N shell.
the M shell

If the quota is filled in the outermost shell of an atom, an element made up of such
to be inert. When the K shell is filled with 2 electrons, we have
1-2b). When the outer shell of an atom
If an atom
so that the
positive ion. If an atom gains electrons,
negative ion. The
by which atoms
gain or lose
called ionization.
Example 1.3 Describe


29

fill

is said

is

+ 1.

THE ELECTRIC CHARGE

Since
(-), electric

(+),

polarity.
When a pair of objects contains
objects are said to have like charges. When a pair of bodies
is negative (-), they
body is positive (+) while the
law of electric
may be stated as follows:
charges.

1 Like

(+) or both


is, one
said to have unlike or opposite

each other; unlike charges attract each other.

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(-), the

I


4

THE NATURE OF ELECTRICITY

[CHAP. 1

If a negative (-) charge placed next another negative (-) charge,
1-4a). If a positive (+) charge is placed next to a negative (-) charge,
1-4c).
together

Like - charges repel

Like

+ charges repel

(4


will be drawn

Unlike charges attract

(c)

(b)

Fig. 1-4 Force

THE COULOMB
The magnitude of electric
a body possesses
of electrons
compared
the number of protons within the
The symbol for the magnitude of the
electric
Q, expressed in units of coulombs (C). A charge of one
-Q,
means a body
a charge of 6.25 x 10" more electrons
Example 1.4 What the meaning of +Q?
A charge of one
electrons.
Example 1.5 A dielectric
coulombs?
Since the number of electrons


of 6.25 x 10l8 more protons

of 12.5 X 10'8 electrons.

a negative

is its

in

of 1 C (1 C = 6.25 x 10'* electrons), - Q = 2 C.

THE ELECTROSTATIC FIELD
The
of an electric
present within the electrostatic field surrounding

is its

to exert a force. This force is

1-5). The electric field is indicated by lines of force drawn
If an electron is released at point A in this field, it will be
by the
Electrostatic lines of force

Fig. 1-5 The

field between


*See page 16 for an explanation of how to use powers of 10.

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of opposite


5

T H E NATURE OF ELECTRICITY

CHAP. 11

and will be attracted to the
direction of motion that would be taken by the electron if it
electrostatic field.

1-5 indicate
in different areas of the

Example 1.0 Draw the electrostatic field that would exist between two negatively charged objects.

When two like charges are placed near each other, the lines of force repel each other as shown below.

<

A charged object will retain
to or
electricity.


if there is no immediate transfer of electrons
at rest. Electricity at rest is called static

POTENTIAL DIFFERENCE

Because of the force of its

potential. When one

field, an electric
is different

electromotive force (emf).
of potential
The basic
indicating the ability to do
voltage.

volt (V). The

for potential

is V,

Example 1.7 What is the meaning of a battery voltage output of 6 V?
A voltage output of 6 V means that the potential difference between the two terminals of the battery is
6 V. Thus, voltage is fundamentally the potential difference between two points.

CURRENT


The
current. To produce current, the
must
moved by a potential
Current
I. The
basic
in which current is measured is the
(A). One
of current is defined as the
movement of one
Example 1.8 If a current of 2 A flows through a meter for 1 minute (min), how many coulombs pass through
the meter?
1 A is 1 C per second (C/s). 2 A is 2 C/s. Since there are 60 s in 1 min, 60 x 2 C = 120 C pass through
the meter in 1 min.

The definition of current can

as an equation:

I = -Q

T

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6

THE NATURE OF ELECTRICITY


where

[CHAP. 1

I = current, A
Q = charge,
T = time, s
Q = I x T = IT

or

in that Q is

Charge differs from
intensity of moving charges.
Example 1.Q Find the
Write down the

( 1-21

accumulation of charge, while I measures the

to Example 1.8 by using

I = 2A

(1-2).
T=Ws


Q=?

Use Eq. (1-2) to solve for the
Q = I x T

Substitute I = 2 A and T = 60 s:
Q = (2A) x (60s)

Solve for Q:
Q = 120C

Ans.

CURRENT FLOW
In
a potential difference. If a
difference is connected
two ends
of a copper wire (Fig. M),the applied voltage (1.5 V) forces
a drift of electrons
-0, at one end of the wire, moving
through the wire, and returning to the positive charge, +Q, at the
end. The
of the
electron
is from
negative side of the
through the wire, and back to the positive
side of the
The

of electron flow is from a point of negative potential to a point
of positive potential. The solid arrow (Fig. 1-6) indicates
Conventional flow

+----

Electron flow
Free electrons
in motion

Copper wire
conductor

r

I

\
Potential

Battery cell
= 1.5 V

Fig. 1-6 Potential

across two
ends of a wire conductor causes
electric current

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THE NATURE OF ELECTRICITY

CHAP. I]

7

electron flow. The direction of moving positive charges,
from electron flow, is conconventional flow of current and is indicated by the
1-6). In
sidered
electricity,
are usually analyzed in terms of conventional

book current

always

considered as conventional flow.
SOURCES OF ELECTRICITY
Chemical Battery

A
chemical cell is a combination of materials which are used for converting chemical
is formed when two or more cells are connected. A
energy. A
energy into
chemical reaction
1-7). The metals are in contact with an electrolyte.

Metal

Electrolyte

Fig. 1-7 Voltaic

cell

Generator

The
is a machine in which electromagnetic inductance is used to produce a voltage by
rotating coils of wire through a
magnetic field or by rotating a magnetic field through
stationary coils of wire. Today more than 95 percent of the world's energy is produced by
generators.
Thermal Energy

The
of most electric energy begins with the formation of heat energy. Coal, oil, or
natural gas can be burned to release large quantities of heat. Once heat energy is available,
conversion to mechanical energy is the next step. Water is heated to produce steam, which is then
used to turn
direct conversion from heat energy
to electric energy will increase efficiency and reduce thermal pollution of water
and the
atmosphere.
Magnetohydrodynamic (MHD)Conversion

In MHD converter, gases are ionized by very high temperatures, approximately 3000 degrees

Fahrenheit (3000°F), or 1650 degrees Celsius (1650'C). The hot gases pass through a strong
magnetic field with current resulting. The
1-8). MHD converters have no mechanical moving parts.
Thermionic Emission

The thermionic energy converter
emitter

a device that

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of two electrodes in a vacuum. The


T H E NATURE OF ELECTRICITY

[CHAP. 1

Fig. 1-8 Principles of M H D converter

Solar Cells
Solar cells convert light energy directly into electric energy. They consist of semiconductor
Solar cells are
material like

Piezoelectric Effect
Certain crystals, such as quartz and Rochelle salts, generate a voltage when they are vibrated
mechanically. This action is known as the piezoelectric efect. One example is the crystal
phonograph cartridge, which contains a Rochelle salt crystal to which a needle is fastened. As the

from side to side. This mechanical motion is
needle moves in the grooves of a record, it
applied to the crystal, and a voltage then generated.
Photoelectric Effect
Some materials, such as zinc, potassium, and cesium oxide, emit electrons when light strikes
their surfaces. This action is known as the photoelectric efect. Common applications of photoelectricity are television camera tubes and photoelectric cells.
Thermocouples
If wires of two different metals, such as iron and copper, are welded together and the joint is
heated, the difference in electron activity in the two metals produces an emf across the
joint. Thermocouple junctions can be used to measure the amount of current because current acts
to heat the junction.

DIRECT AND ALTERNATING CURRENTS AND VOLTAGES
Direct current (dc) is current that moves through a conductor or circuit in one direction only
(Fig. 1-90). The reason for the unidirectional current is that voltage sources such as cells and
batteries maintain the same polarity of output voltage
1-9b). The voltage supplied by these
sources is
direct-current voltage, or simply dc uoltage. A dc voltage source can change the
amount of its output voltage, but if the same polarity is maintained, direct current will flow in one
direction only.

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9

THE NATURE OF ELECTRICITY

CHAP. 11


dc Current

+ I

dc Voltage

+ v

9

Magnitude
of current

V

'
1 Magnitude
of voltage
-T

6

0
Time

0

+


Fig. 1-9 Waveforms of a constant

dc voltage

Example 1.10 Assuming the polarity of the
current and
With polarity reversed, the current will now flow in the

o

r

Fig. 1-9b,draw

v~

new curves of

0~

- v

- I
dc Current

dc

An alternating-current
(ac voltage)
periodically reverses or alternates in polarity

(Fig. 1- 10a). Therefore, the resulting
current also
reverses direction
1-lob). In terms of conventional flow, the current flows from
common
these systems.

The voltage

power line
in most
is a
current direction go through many reversals each second in

ac

ac Current

(b)

(0)

Fig. 1-10 Waveforms of ac voltage

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ac current


10


THE NATURE OF ELECTRICITY

[CHAP. 1

Solved Problems
1.1

meaning in column 2.

Match each term in column 1 to its
Column 1
Electron
Neutron
Compound
Neutral
Valence electrons
Atomic number
Free
K shell
Ion
Inert

1.

2.
3.
4.

5.

6.

7.
8.
9.
10.

(a)

(b)
(c)

(d)
(e)

cf)
(8)

(h)
(i)
(j)

(k)
(I)
(m)
Ans.

1.2

1. (i)


Column 2
Positive charge
Same number of electrons and protons
Electrons in first shell
Released electrons
Neutral
Electrons in outermost shell
Quota filled in outermost shell
Number of electrons in nucleus
Negative charge
Quota of 2 electrons
Combined elements
Number of protons in nucleus
Charged atom
7. ( d ) 8. (j) 9. (m) 10. (g)

3. (k) 4. ( b ) 5 . (f) 6 . (I)

2. (e)

Show the
electron

of the element aluminum with atomic number 13. What is its

Because aluminum has 13 protons in the
electrically

it must have 13 orbiting

1-3), we have

K shell
L shell
M shell
Total

2 electrons
8 electrons
3 electrons
13 electrons

The atomic structure for aluminum then is shown in Fig. 1-11. Its electron
has 3 valence

/&,
' -0".
Q
,'a ,&,
I

/

//

i
/

I


\

/

/

\

\

\

\

\

L

\

\
M
\

3 electrons in 18-electron
shell
'

/-


\

\

to be

2-electron

-0-2,.
'.--/\
8-electron

Fig. 1-11

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-3 because it


CHAP. I]

1.3

11

T H E NATURE OF ELECTRICITY

In observing the maximum number of electrons in shells K, L, M,and N in Fig. 1-3, you will
find that they are 2, 8, 18, and 32 electrons, respectively.
a formula that describes

n is the shell
in sequential order outward
the nucleus.
this
The

2n2 because the maximum number of electrons in the

K or
shell (n = 1) is
= 2(1) = 2
L or
shell (n = 2) is 2(23 = 2(4) = 8
M or
shell (n = 3) is 2(33 = 2(9) = 18
N or fourth shell (n = 4) is 2(43 = 2(16) = 32
This

1.4

What is the net charge of a body that contains 8 protons and 4 electrons?
The numerical
of the net charge is found by
from the number of the other type. So a
yields
4 (+4).

1.5

the number of one type of charge

8 (+8) and
4 (-4)

50 x 10l8 electrons.

A charged
with

its charge in coulombs

Since C = 6.25 x 10" electrons, 8 C = 50 x 10" electrons. Deficiency of electrons
excess of protons. So the
8 C, or + Q = 8 C.
1.6

Write the word
( a ) A rubber

so both

fur. If the

( b ) Glass
the glass
( a ) like (law of charges);

1.7

an


rod is negative,

(b) positive (law of charges)

Find the current needed to charge a dielectric so that it will accumulate a charge of 20C
after 4 s.
Known
Unknown:

Q = 20C; T = 4 s

I=?

Use Eq. (1-1) to find I:

I = - = - -* O C - 5 A
T
4s
1.8

Ans.

A current of 8 A charges an insulator for 3 s. How
Known
Unknown:

I = 8 A; T = 3 s
Q=?

Use Eq. (1-2) to find Q:


Q
1.9

Write the word or words
( a ) The

=

IT = (8 A)(3 s) = 24 C

Ans.

correctly complete each of the following statements.

of a charge to do work is its

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THE NATURE OF ELECTRICITY

12

[CHAP. 1

When one charge is different

of charges
value for the current.

a
A greater amount of moving charges
When the potential
is
The rate of flow of charge is called
The direction of the
flow of current is from a point of
potential.
potential to a point of
Electron flow is opposite in direction to
flow.
direction.
Direct current (dc) has just
is an example of a dc voltage source.
A
its polarity.
An alternating current (ac)
( a ) potential

(b) difference, potential
(c) volt
(d) electromotive force
(e) current
(f) higher

( h ) current
(i) positive, negative
(j) conventional
(k) one
( I ) battery

(m) reverses

( 8 ) zero

1.10

Match each device in column 1 to its closest principle in column 2.
1.

2.
3.
4.

5.

Column 1
Battery
Generator
TV camera tube
Vacuum tube
Phonograph

(a)

(b)
(c)
(d)
(e)

cf)

(g)
Ans.

1. ( d ) 2 . (a) 3.

(1)

Column 2
Electromagnetic
Free electrons
Ionized
Chemical
Thermal
Photoelectricity
Mechanical

4. ( b ) 5 . ( g )

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THE NATURE OF ELECTRICITY

CHAP. I]

Supplementary Problems
1.11

Match


2
1. Proton

( a ) Negative

(b) Quota of 8 electrons
(c) Excited state
( d ) Maximum number of electrons in a shell
(e) Atom negatively
cf) Positive
(g) Mass and volume
( h ) Atomic number is 29
(i) Quota of 18 electrons
(j) Orbit
(k) Smallest
having same
characteristics
(I) Atomic
is 14
(m) All atoms

2. Molecule
3. Quota
4. L shell
5. Element
6. Unstable
7. Shell
8. Copper
9. Negative
10. Matter


Ans. 1. cf) 2. (k) 3. ( d ) 4. ( b ) 5. (m) 6. (c)
1.12

Write

7. (j) 8. ( h ) 9. (e)

10. ( g )

word or words which most

( a ) Electrons move about the

of an atom in paths which are
(b) The nucleus of an atom consists of particles called
(c) The
of protons in the
of an atom is known as the
of that
( d ) When all the
within a substance are alike,

(4 A

cf)
(8)

(h)
(i)

(j)

is
compound.
of an electron
The energy
atom.
If a neutral
If a neutral
Unlike charges
each other, while like charges
A charged object is surrounded by an
field.

Ans. ( a ) shells or orbits
(b) protons,
( c ) atomic
( d ) element
(e) molecule

each

cf) level
(8) negative
(h) positive
(i) attract, repel
(j) electrostatic

1.13


Show the atomic structure of the element
which has an atomic
Ans. See Fig. 1-12. Electron
-5.
electron

1.14

Show the
valence?

1.15

What is

of 15. What is its

structure of the element
which has
of 10. What is its
Ans. See Fig. 1-13. Electron
0. Thus, neon is inert.

if 13 electrons are added to 12 protons?

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Ans. -1 electron



14

THE NATURE OF ELECTRICITY

Fig. 1-12

1.16

[CHAP. 1

Fig. 1-13

What becomes of the
Ans. It

of -4.

Fig. 1-2c.

1.17

A charged
Ans. - Q = 4 C

1.18

A material with an excess of 25 x 10'' electrons
6.25 x 10l8electrons. The excess electrons are
then
to flow past a given point in 2s. Find the current produced by the resultant

~ n s .r = 1 . 5 ~
flow.

1.19

A charge of 10 C flows past

1.20

How much charge
Ans. Q = 2 5 C

1.21

Match

2. Cesium
3. Silicon

1.22

given point

2 s. What

Section 2
Solar cell
(b) Generator
( c ) Battery
( d ) Crystal

(a)

3. (a) 4. (d) 5. (c) 6. ( h )

Fill in the missing quantity:

1, A

Q,C

?

10
?
9
?

5
?
7
2

Ans. I = 5 A

in section 2.

Section 1
4. Quartz
5. Carbon-zinc
6. Iron-copper


1. (f) 2. (e)

the current?

of 5 A charges an insulator for 5 s?

item in section 1 with its

1. Water

Ans.

of 25 x 10" electrons. Find its charge in coulombs with polarity.

6

Ans.

2
4
2
3
?
-

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Photoelectric sell
(f) Turbine

(g) MHD converter
( h ) Thermocouple
(e)