Chapter 01

Allan R. Hambley, Electrical Engineering: Principles and Applications, Third Edition, ISBN 0-13-147046-9
© 2005 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. This material is protected under all copyright laws as they currently
exist. No portion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.

CHAPTER 1

Exercises

E1.1 Charge = Current × Time = (2 A) × (10 s) = 20 C

dq (t ) d
E1.2 i (t ) = = (0.01sin(200t) = 0.01 × 200cos(200t ) = 2cos(200t ) A
dt dt

E1.3 Because i2 has a positive value, positive charge moves in the same
direction as the reference. Thus positive charge moves downward in
element C.

Because i3 has a negative value, positive charge moves in the opposite
direction to the reference. Thus positive charge moves upward in
element E.

E1.4 Energy = Charge × Voltage = (2 C) × (20 V) = 40 J

Because vab is positive, the positive terminal is a and the negative
terminal is b. Thus the charge moves from the negative terminal to the
positive terminal, and energy is removed from the circuit element.

E1.5 iab enters terminal a. Furthermore, vab is positive at terminal a. Thus
the current enters the positive reference, and we have the passive
reference configuration.

E1.6 (a) pa (t ) = v a (t )ia (t ) = 20t 2
10 10 10
20t 3 20t 3
w a = ∫ pa (t )dt = ∫ 20t dt = 2
= = 6667 J
0 0
3 0
3
(b) Notice that the references are opposite to the passive sign
convention. Thus we have:

pb (t ) = −v b (t )ib (t ) = 20t − 200
10 10
10
w b = ∫ pb (t )dt = ∫ (20t − 200)dt = 10t 2 − 200t 0
= −1000 J
0 0

1


E1.7 (a) Sum of currents leaving = Sum of currents entering
ia = 1 + 3 = 4 A

(b) 2 = 1 + 3 + ib ⇒ ib = -2 A

(c) 0 = 1 + ic + 4 + 3 ⇒ ic = -8 A

E1.8 Elements A and B are in series. Also, elements E, F, and G are in series.

E1.9 Go clockwise around the loop consisting of elements A, B, and C:
-3 - 5 +vc = 0 ⇒ vc = 8 V

Then go clockwise around the loop composed of elements C, D and E:
- vc - (-10) + ve = 0 ⇒ ve = -2 V

E1.10 Elements E and F are in parallel; elements A and B are in series.

ρL
E1.11 The resistance of a wire is given by R = . Using A = πd 2 / 4 and
A
substituting values, we have:

1.12 × 10 −6 × L
9. 6 = ⇒ L = 17.2 m
π (1.6 × 10 − 3 )2 / 4

E1.12 P =V 2 R ⇒ R =V 2 / P = 144 Ω ⇒ I = V / R = 120 / 144 = 0.833 A

E1.13 P =V 2 R ⇒ V = PR = 0.25 × 1000 = 15.8 V
I = V / R = 15.8 / 1000 = 15.8 mA

E1.14 Using KCL at the top node of the circuit, we have i1 = i2. Then using KVL
going clockwise, we have -v1 - v2 = 0; but v1 = 25 V, so we have v2 = -25 V.
Next we have i1 = i2 = v2/R = -1 A. Finally, we have
PR = v 2i2 = ( −25) × ( −1) = 25 W and Ps = v 1i1 = (25) × ( −1) = −25 W.

E1.15 At the top node we have iR = is = 2A. By Ohm’s law we have vR = RiR = 80
V. By KVL we have vs = vR = 80 V. Then ps = -vsis = -160 W (the minus sign
is due to the fact that the references for vs and is are opposite to the
passive sign configuration). Also we have PR = v R iR = 160 W.

2


Problems

P1.1 Four reasons that non-electrical engineering majors need to learn the
fundamentals of EE are:

1. To pass the Fundamentals of Engineering Exam.
2. To be able to lead in the design of systems that contain
electrical/electronic elements.
3. To be able to operate and maintain systems that contain
electrical/electronic functional blocks.
4. To be able to communicate effectively with electrical engineers.

P1.2 Eight subdivisions of EE are:

1. Communication systems.
2. Computer systems.
3. Control systems.
4. Electromagnetics.
5. Electronics.
6. Photonics.
7. Power systems.
8. Signal Processing.

P1.3 (a) Electrical current is the time rate of flow of net charge through a
conductor or circuit element. Its units are amperes, which are equivalent
to coulombs per second.

(b) The voltage between two points in a circuit is the amount of energy
transferred per unit of charge moving between the points. Voltage has
units of volts, which are equivalent to joules per coulomb.

(c) The current through an open switch is zero. The voltage across the
switch can be any value depending on the circuit.

(d) The voltage across a closed switch is zero. The current through the
switch can be any value depending of the circuit.

3


(e) Direct current is constant in magnitude and direction with respect to
time.

(f) Alternating current varies either in magnitude or direction with time.

P1.4 (a) A conductor is anagolous to a frictionless pipe.
(b) An open switch is anagolous to a closed valve.
(c) A resistance is anagolous to a constriction in a pipe or to a pipe with
friction.
(d) A battery is analogous to a pump.

1 coulomb/s
P1.5 Electrons per second = = 6.25 × 1018
1.60 × 10 coulomb/electron
−19

P1.6* The reference direction for iab points from a to b. Because iab has a
negative value, the current is equivalent to positive charge moving
opposite to the reference direction. Finally since electrons have negative
charge, they are moving in the reference direction (i.e., from a to b).

For a constant (dc) current, charge equals current times the time
interval. Thus, Q = (5 A) × (3 s) = 15 C.

dq (t ) d
P1.7* i (t ) = = (2 + 3t ) = 3 A
dt dt

P1.8 (a) The sine function completes one cycle for each 2π radian increase in
the angle. Because the angle is 200πt , one cycle is completed for each
time interval of 0.01 s. The sketch is:

4


0.005 0.005
0.005
(b) Q = ∫ i (t )dt = ∫ 10 sin(200πt )dt = (10 / 200π ) cos(200πt ) 0
0 0

= 0.0318 C
0.01 0.01
0.01
(c) Q = ∫ i (t )dt = ∫ 10 sin(200πt )dt = (10 / 200π ) cos(200πt ) 0
0 0

=0 C

∞ ∞
P1.9* Q = ∫ i (t )dt = ∫ 2e −t dt = −2e −t | 0 = 2 coulombs
∞

0 0

dq (t ) d
P1.10 i (t ) =
dt
=
dt
(3 − 3e −2t ) = 6e −2t A

P1.11 The number of electrons passing through a cross section of the wire per
second is
15
N = = 9.375 × 1019 electrons/second
1.6 × 10 − 19

The volume of copper containing this number of electrons is

9.375 × 1019
volume = = 9.375 × 10 − 10 m3
10 29

The cross sectional area of the wire is

πd 2
A= = 3.301 × 10 − 6 m2
4

Finally, the average velocity of the electrons is
volume
u = = 0.2840 mm/s
A

P1.12 The electron gains 1.6 × 10 −19 × 9 = 14.4 × 10 −19 joules

P1.13* Q = current × time = (5 amperes) × (36,000 seconds) = 1.8 × 10 5 coulombs
Energy = QV = (1.8 × 10 5 ) × (12) = 2.16 × 10 6 joules

5


P1.14* (a) P = -vaia = -20 W Energy is being supplied by the element.
(b) P = vbib = 50 W Energy is being absorbed by the element.
(c) P = -vcic = 40 W Energy is being absorbed by the element.

P1.15 The amount of energy is W = QV = (3 C) × (10 V) = 30 J. Because the
reference polarity is positive at terminal a and the voltage value is
negative, terminal b is actually the positive terminal. Because the charge
moves from the negative terminal to the positive terminal, energy is
removed from the device.

P1.16 Q = w V = (600 J) (12 V) = 50 C . To increase the chemical energy stored
in the battery, positive charge should move from the positive terminal to
the negative terminal, in other words from a to b. Electrons move from b
to a.

P1.17 p (t ) = v (t )i (t ) = 20e −t W
∞
Energy = ∫ p (t )dt = −20e −t | 0 = 20 joules
∞

0

The element absorbs the energy.

P1.18 ( a) p (t ) = v ab iab = 50 sin(200πt ) W

0.005 0.005
0.005
(b) w = ∫ p (t )dt = ∫ 50 sin(200πt )dt = (50 / 200π ) cos(200πt ) 0
0 0

= 0.1592 J
0.01 0.01
0.01
(c) w = ∫ p (t )dt = ∫ 50 sin(200πt )dt = (50 / 200π ) cos(200πt ) 0
0 0

=0 J

6


Cost $40
P1.19* Energy = = = 400 kWh
Rate 0.1 $/kWh

Energy 400 kWh P 555.5
P = = = 555.5 W I = = = 4.630 A
Time 30 × 24 h V 120

40
Reduction = × 100% = 7.20%
555.5

P1.20 (a) P = 60 W delivered to element A.
(b) P = 60 W taken from element A.
(c) P = 60 W delivered to element A.

P1.21* (a) P = 60 W taken from element A.
(b) P = 60 W delivered to element A.
(c) P = 60 W taken from element A.

P1.22 The power that can be delivered by the cell is p = vi = 0.12 W. In 75
hours, the energy delivered is W = pT = 9 Whr = 0.009 kWhr. Thus the
unit cost of the energy is Cost = (0.50) /( 0.009) = 55.56 $/kWhr which is
556 times the typical cost of energy from electric utilities.

P1.23 The current supplied to the electronics is i = p /v = 50 / 12.6 = 3.968 A.
The ampere-hour rating of the battery is the operating time to discharge
the battery multiplied by the current. Thus, the operating time is
T = 100 / i = 25.2 hours. The energy delivered by the battery is
W = pT = 50(25.2) = 1260 wh = 1.26 kWh. Neglecting the cost of
recharging, the cost of energy for 300 discharge cycles is
Cost = 75 /(300 × 1.26) = 0.1984 $/kWh.

P1.24 The currents in series-connected elements are equal.

P1.25 For a proper fluid analogy to electric circuits, the fluid must be
incompressible. Otherwise the fluid flow rate out of an element could be
more or less than the inward flow. Similarly the pipes must be inelastic
so the flow rate is the same at all points along each pipe.

7


P1.26* Elements A and B are in series. Also elements E and F are in series.

P1.27 (a) Elements C and D are in series.
(b) Because elements C and D are in series, the currents are equal in
magnitude. However, because the reference directions are opposite, the
algebraic signs of the current values are opposite. Thus, we have ic = −id .
(c) At the node joining elements A, B, and C, we can write the KCL
equation ib = ia + ic = 3 + 1 = 4 A . Also we found earlier that
id = −ic = −1 A.

P1.28* At the node joining elements A and B, we have ia + ib = 0. Thus, ia = −2 A.
For the node at the top end of element C, we have ib + ic = 3 . Thus,
ic = 1 A . Finally, at the top right-hand corner node, we have
3 + ie = id . Thus, id = 4 A . Elements A and B are in series.

P1.29* We are given ia = 2 A, ib = 3 A, id = −5 A, and ih = 4 A. Applying KCL, we find

ic = ib − ia = 1 A ie = ic + ih = 5 A
if = ia + id = −3 A i g = if − ih = −7 A

P1.30 We are given ia = −1 A, ic = 3 A, i g = 5 A, and ih = 1 A. Applying KCL, we find

ib = ic + ia = 2 A ie = ic + ih = 4 A
id = if − ia = 7 A if = i g + ih = 6 A

P1.31 (a) Elements A and B are in parallel.
(b) Because elements A and B are in parallel, the voltages are equal in
magnitude. However because the reference polarities are opposite, the
algebraic signs of the voltage values are opposite. Thus, we have
v a = −v b .
(c) Writing a KVL equation while going clockwise around the loop
composed of elements A, C and D, we obtain v a − v d − v c = 0. Solving for
v c and substituting values, we find v c = 7 V. Also we have
v b = −v a = −2 V.

8


P1.32* Summing voltages for the lower left-hand loop, we have − 5 + v a + 10 = 0,
which yields v a = −5 V. Then for the top-most loop, we have
v c − 15 − v a = 0, which yields v c = 10 V. Finally, writing KCL around the
outside loop, we have − 5 + v c + v b = 0, which yields v b = −5 V.

P1.33 We are given v a = 5 V, v b = 7 V, vf = −10 V, and v h = 6 V. Applying KVL, we
find
v d = v a + v b = 12 V v c = −v a − vf − v h = −1 V
v e = −v a − v c + v d = 8 V v g = ve − v h = 2 V
v b = vc + ve = 7 V

P1.34* Applying KCL and KVL, we have
ic = ia − id = 1 A ib = −ia = −2 A
v b = v d − v a = −6 V vc = vd = 4 V
The power for each element is
PA = −v a ia = −20 W PB = v b ib = 12 W
PC = v c ic = 4 W PD = v d id = 4 W
Thus, PA + PB + PC + PD = 0

P1.35 (a) In Figure P1.28, elements C, D, and E are in parallel.
(b) In Figure P1.33, no element is in parallel with another element.
(c) In Figure P1.34, elements C and D are in parallel.

P1.36 The points and the voltages specified in the problem statement are:

Applying KVL to the loop abca, substituting values and solving, we obtain:
v ab − v cb − v ac = 0
5 − 15 − v ac = 0 v ac = −10 V

9


Similiarly, applying KVL to the loop abcda, substituting values and solving,
we obtain:

v ab − v cb + v cd + v da = 0
5 − 15 + v cd − 10 = 0
v cd = 20 V

P1.37*

P1.38

P1.39 Four types of controlled sources are:
1. Voltage-controlled voltage sources.
2. Voltage-controlled current sources.
3. Current-controlled voltage sources.
4. Current-controlled current sources.

P1.40 The resistance of the copper wire is given by RCu = ρCu L A , and the
resistance of the tungsten wire is RW = ρW L A . Taking the ratios of the
respective sides of these equations yields RW RCu = ρW ρCu . Solving for
RW and substituting values, we have

RW = RCu ρW ρCu
= (0.5) × (5.44 × 10 -8 ) (1.72 × 10 −8 )
= 1.58 Ω

10


P1.41

P1.42

P1.43* R=
( 1 )2
V
=
1002
= 100 Ω
P1 100
( 2)
2
V 90 2
P2 = = = 81 W for a 19% reduction in power
R 100

P1.44 The power delivered to the resistor is
p (t ) = v 2 (t ) / R = 2.5 exp( −4t )
and the energy delivered is

∞ ∞ ∞
 2. 5  2. 5
w = ∫ p (t )dt = ∫ 2.5 exp(−4t )dt =  exp( −4t ) = = 0.625 J
0 0 − 4 0 4

P1.45 The power delivered to the resistor is
p (t ) = v 2 (t ) / R = 2.5 sin 2 (2πt ) = 1.25 − 1.25 cos( 4πt )
and the energy delivered is

10 10 10
 1.25 
w = ∫ p (t )dt = ∫ [1.25 − 1.25 cos( 4πt )]dt = 1.25t − sin( 4πt ) = 12.5 J
0 0  4π 0

11


P1.46 Equation 1.10 gives the resistance as
ρL
R =
A
(a) Thus, if the length of the wire is doubled, the resistance doubles to
1Ω.
(b) If the diameter of the wire is doubled, the cross sectional area A is
increased by a factor of four. Thus, the resistance is decreased by
a factor of four to 0.125 Ω .

P1.47 The power for each element is 20 W. The current source delivers power
and the voltage source absorbs it.

P1.48*

As shown above, the 2 A current circulates clockwise through all three
elements in the circuit. Applying KVL, we have

v c = v R + 10 = 5iR + 10 = 20 V

Pcurrent − source = −v c iR = −40 W. Thus, the current source delivers power.

PR = (iR ) 2 R = 22 × 5 = 20 W. The resistor absorbs power.

Pvoltage − source = 10 × iR = 20 W. The voltage source absorbs power.

P1.49 This is a parallel circuit and the voltage across each element is 10 V
positive at the top end. Thus, the current through the resistor is
10 V
iR = = 2A
5Ω
Applying KCL, we find that the current through the voltage source is
zero. Computing power for each element, we find

Pcurrent − source = −20 W

12


Thus, the current source delivers power.

PR = (iR ) 2 R = 20 W

Pvoltage − source = 0

P1.50*

Applying Ohm's law, we have v 2 = (5 Ω ) × (1 A) = 5 V . However,v 2
is the voltage across all three resistors that are in parallel. Thus,
v2 v2
i3 = = 1 A , and i2 = = 0.5 A . Applying KCL, we have
5 10
i1 = i2 + i3 + 1 = 2.5 A . By Ohm's law: v 1 = 5i1 = 12.5 V . Finally using KVL,
we havev x = v 1 + v 2 = 17.5 V .

P1.51

Ohm’s law for the 5-Ω resistor yields: i1 = 15 / 5 = 3 A. Then for the 10-Ω
resistor, we have v 1 = 10i1 = 30 V. Using KVL, we have v 2 = v 1 + 15 = 45 V.
Then applying Ohms law, we obtain i2 = v 2 / 10 = 4.5 A. Finally applying
KCL, we have I x = i1 + i2 = 7.5 A.

13


P1.52* (a) Applying KVL, we have 10 = v x + 5v x , which yields v x = 10 / 6 = 1.667 V
(b) ix = v x / 3 = 0.5556 A
(c) Pvoltage − source = −10ix = −5.556 W. (This represents power delivered by
the voltage source.)
PR = 3(ix ) 2 = 0.926 W (absorbed)
Pcontrolled − source = 5v x ix = 4.63 W (absorbed)

P1.53

Applying KVL around the periphery of the circuit, we have
− 18 + v x + 2v x = 0, which yields v x = 6 V. Then we have v 12 = 2v x = 12 V.
Using Ohm’s law we obtain i12 = v 12 / 12 = 1 A and i x = v x / 2 = 3 A. Then
KCL applied to the node at the top of the 12-Ω resistor gives i x = i12 + i y
which yields i y = 2 A.

P1.54 Consider the series combination shown below on the left. Because the
current for series elements must be the same and the current for the
current source is 2 A by definition, the current flowing from a to b is 2
A. Notice that the current is not affected by the 10-V source in series.
Thus, the series combination is equivalent to a simple current source as
far as anything connected to terminals a and b is concerned.

14


P1.55 Consider the parallel combination shown below. Because the voltage for
parallel elements must be the same, the voltage vab must be 10 V. Notice
that vab is not affected by the current source. Thus, the parallel
combination is equivalent to a simple voltage source as far as anything
connected to terminals a and b is concerned.

P1.56 (a) 10 = v 1 + v 2
(b) v 1 = 15i
v 2 = 5i
(c) 10 = 15i + 5i
i = 0.5 A
(d) P
voltage −source = −10i = −5 W. (Power delivered by the source.)

P15 = 15i 2 = 3.75 W (absorbed)
P5 = 5i 2 = 1.25 W (absorbed)

P1.57*

v x = (4 Ω) × (1 A) = 4 V is = v x / 2 + 1 = 3 A

Applying KVL around the outside of the circuit:

v s = 3is + 4 + 2 = 15 V

15


P1.58 ix = −30 V/15 Ω = −2 A
Applying KCL for the node at the top end of the controlled current
source:
is = ix / 2 − ix = −ix / 2 = 1 A
The source labled is is an independent current source. The source labeled
ix/2 is a current-controlled current source.

P1.59 Applying Ohm's law and KVL, we have 20 + 10ix = 5ix . Solving, we obtain
ix = −4 A.
The source labeled 20 V is an independent voltage source. The source
labeled 5ix is a current-controlled voltage source.

16

Chapter 01

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Chapter 01 (20)

More from federicoblanco (19)

Chapter 01