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Solucionario de Análisis de Circuitos en Ingeniería 7ma edicion Hayt&Kemmerly

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Solucionario de Análisis de Circuitos en Ingeniería 7ma edicion Hayt&Kemmerly

1. 1. Engineering Circuit Analysis, 7th Edition 1. (a) 12 μs (b) 750 mJ (c) 1.13 kΩ (d) 3.5 Gbits (e) 6.5 nm (f) 13.56 MHz Chapter Two Solutions 10 March 2006 (g) 39 pA (h) 49 kΩ (i) 11.73 pA PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
2. 2. Engineering Circuit Analysis, 7th Edition 2. (a) 1 MW (b) 12.35 mm (c) 47. kW (d) 5.46 mA (e) 33 μJ (f) 5.33 nW (g) 1 ns (h) 5.555 MW Chapter Two Solutions 10 March 2006 (i) 32 mm PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
3. 3. Engineering Circuit Analysis, 7th Edition 3. (a) Chapter Two Solutions ⎛ 745.7 W ⎞ ⎟ = 298.3 ⎝ 1 hp ⎠ ( 400 Hp ) ⎜ 10 March 2006 kW ⎛ 12 in ⎞ ⎛ 2.54 cm ⎞ ⎛ 1 m ⎞ (b) 12 ft = (12 ft) ⎜ ⎟⎜ ⎟⎜ ⎟ = 3.658 m ⎝ 1 ft ⎠ ⎝ 1 in ⎠ ⎝ 100 cm ⎠ (c) 2.54 cm = 25.4 mm ⎛ 1055 J ⎞ (d) ( 67 Btu ) ⎜ ⎟ = 70.69 ⎝ 1 Btu ⎠ (e) 285.4´10-15 s = kJ 285.4 fs PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
4. 4. Engineering Circuit Analysis, 7th Edition 4. Chapter Two Solutions 10 March 2006 (15 V)(0.1 A) = 1.5 W = 1.5 J/s. 3 hrs running at this power level equates to a transfer of energy equal to (1.5 J/s)(3 hr)(60 min/ hr)(60 s/ min) = 16.2 kJ PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
5. 5. Engineering Circuit Analysis, 7th Edition 5. Chapter Two Solutions 10 March 2006 Motor power = 175 Hp (a) With 100% efficient mechanical to electrical power conversion, (175 Hp)[1 W/ (1/745.7 Hp)] = 130.5 kW (b) Running for 3 hours, Energy = (130.5×103 W)(3 hr)(60 min/hr)(60 s/min) = 1.409 GJ (c) A single battery has 430 kW-hr capacity. We require (130.5 kW)(3 hr) = 391.5 kW-hr therefore one battery is sufficient. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
6. 6. Engineering Circuit Analysis, 7th Edition 6. Chapter Two Solutions 10 March 2006 The 400-mJ pulse lasts 20 ns. (a) To compute the peak power, we assume the pulse shape is square: Energy (mJ) 400 20 Then t (ns) P = 400×10-3/20×10-9 = 20 MW. (b) At 20 pulses per second, the average power is Pavg = (20 pulses)(400 mJ/pulse)/(1 s) = 8 W. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
7. 7. Engineering Circuit Analysis, 7th Edition 7. Chapter Two Solutions 10 March 2006 The 1-mJ pulse lasts 75 fs. (a) To compute the peak power, we assume the pulse shape is square: Energy (mJ) 1 75 Then t (fs) P = 1×10-3/75×10-15 = 13.33 GW. (b) At 100 pulses per second, the average power is Pavg = (100 pulses)(1 mJ/pulse)/(1 s) = 100 mW. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
8. 8. Engineering Circuit Analysis, 7th Edition 8. Chapter Two Solutions 10 March 2006 The power drawn from the battery is (not quite drawn to scale): P (W) 10 6 t (min) 5 7 17 24 (a) Total energy (in J) expended is [6(5) + 0(2) + 0.5(10)(10) + 0.5(10)(7)]60 = 6.9 kJ. (b) The average power in Btu/hr is (6900 J/24 min)(60 min/1 hr)(1 Btu/1055 J) = 16.35 Btu/hr. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
9. 9. Engineering Circuit Analysis, 7th Edition 9. Chapter Two Solutions 10 March 2006 The total energy transferred during the first 8 hr is given by (10 W)(8 hr)(60 min/ hr)(60 s/ min) = 288 kJ The total energy transferred during the last five minutes is given by ∫ 300 s 0 10 2 ⎡ 10 ⎤ ⎢ − 300 t + 10 ⎥ dt = − 600 t + 10t ⎣ ⎦ 300 = 1.5 kJ 0 (a) The total energy transferred is 288 + 1.5 = 289.5 kJ (b) The energy transferred in the last five minutes is 1.5 kJ PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
10. 10. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 10 March 2006 charge q = 18t2 – 2t4 C. 10. Total (a) q(2 s) = 40 C. (b) To find the m aximum charge within 0 ≤ t ≤ 3 s, we need to take the second derivitives: f irst and dq/dt = 36t – 8t3 = 0, leading to roots at 0, ± 2.121 s d2q/dt2 = 36 – 24t2 substituting t = 2.121 s into the expression for d2q/dt2, we obtain a value of –14.9, so that this root represents a maximum. Thus, we find a maximum charge q = 40.5 C at t = 2.121 s. (c) The rate of charge accumulation at t = 8 s is dq/dt|t = 0.8 = 36(0.8) – 8(0.8)3 = 24.7 C/s. (d) See Fig. (a) and (b). 50 70 (b) (a) 60 50 0 30 tim e (t) q (C) 40 20 -50 10 0 -100 -10 -20 0 0.5 1 1.5 tim e (s ) 2 2.5 3 -150 0 0.5 1 1.5 i (A ) 2 2.5 PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission. 3
11. 11. Engineering Circuit Analysis, 7th Edition 11. Chapter Two Solutions 10 March 2006 Referring to Fig. 2.6c, ⎧- 2 + 3e −5t A, i1 (t ) = ⎨ 3t ⎩ - 2 + 3e A, t<0 t>0 Thus, (a) i1(-0.2) = 6.155 A (b) i1 (0.2) = 3.466 A (c) To determine the instants at which i1 = 0, we must consider t < 0 and t > 0 separately: for t < 0, - 2 + 3e-5t = 0 leads to t = -0.2 ln (2/3) = +0.0811 s (impossible) for t > 0, -2 + 3e3t = 0 leads to t = (1/3) ln (2/3) = –0.135 s (impossible) Therefore, the current is never negative. (d) The total charge passed left to right in the interval –0. 8 < t < 0.1 s is q(t) = = ∫ 0.1 i (t )dt −0.8 1 0 −5 t ∫−0.8 ⎡ −2 + 3e ⎤ dt ⎣ ⎦ + 0 3 ⎛ ⎞ = ⎜ −2t − e−5t ⎟ 5 ⎝ ⎠ -0.8 + ∫ 0.1 0 ⎡ −2 + 3e3t ⎤ dt ⎣ ⎦ ( −2t + e ) 3t 0.1 0 = 33.91 C PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
12. 12. Engineering Circuit Analysis, 7th Edition 12. Chapter Two Solutions 10 March 2006 Referring to Fig. 2.28, (a) The average current over one period (10 s) is iavg = [-4(2) + 2(2) + 6(2) + 0(4)]/10 = 800 mA (b) The total charge transferred over the interval 1 < t < 12 s is qtotal = ∫ 12 1 i (t )dt = -4(1) + 2(2) + 6(2) + 0(4) – 4(2) = 4 C (c) See Fig. below q (C) 8 -8 16 2 4 10 6 8 12 14 t(s) 16 -16 PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
13. 13. Engineering Circuit Analysis, 7th Edition 13. (a) VBA = – (b) VED = 2 pJ -1.602 × 10-19 C Chapter Two Solutions = 12.48 MV 0 -1.602 × 10-19 C = 0 3 pJ 1.602 × 10-19 C = 10 March 2006 –18.73 MV (c) VDC = – (d) It takes – 3 pJ to move +1.602x10–19 C from D to C. It takes 2 pJ to move –1.602x10–19 C from B to C, or –2 pJ to move –19 C from B to C, or +2 pJ to move +1.602x10–19 C from C to B. +1.602x10 Thus, it requires –3 pJ + 2 pJ = –1 pJ to m ove +1.602x10 –19 C from D to C to B. Hence, VDB = −1 pJ = –6.242 MV. 1.602 × 10-19 C PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
14. 14. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 10 March 2006 14. + V1 – – V2 + + – Voltmeter + Voltmeter From the diagram, we see that V2 = –V1 = +2.86 V. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
15. 15. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 15. (a) Pabs = (+3.2 V)(-2 mA) = –6.4 mW (b) Pabs = (+6 V)(-20 A) = –120 W 10 March 2006 (or +6.4 mW supplied) (or +120 W supplied) (d) Pabs = (+6 V)(2 ix) = (+6 V)[(2)(5 A)] = +60 W (e) Pabs = (4 sin 1000t V)(-8 cos 1000t mA)| t = 2 ms = +12.11 W PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
16. 16. Engineering Circuit Analysis, 7th Edition 16. Chapter Two Solutions 10 March 2006 i = 3te-100t mA and v = [6 – 600t] e-100t mV (a) The power absorbed at t = 5 ms is [ Pabs = (6 − 600t ) e −100t ⋅ 3te −100t = ] t = 5 ms μW 0.01655 μW = 16.55 nW (b) The energy delivered over the interval 0 < t < ∞ is ∫ ∞ 0 Pabs dt = ∫ ∞ 0 3t (6 − 600t ) e − 200t dt μJ Making use of the relationship ∫ ∞ 0 x n e − ax dx = n! a n +1 where n is a positive integer and a > 0, we find the energy delivered to be = 18/(200)2 - 1800/(200)3 = 0 PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
17. 17. Engineering Circuit Analysis, 7th Edition 17. Chapter Two Solutions (a) Pabs = (40i)(3e-100t)| t = 8 ms = [ di ⎞ ⎛ (b) Pabs = ⎜ 0.2 ⎟ i = - 180 e −100t dt ⎠ ⎝ ( t (c) Pabs = ⎛ 30∫ idt + 20 ⎞ 3e −100t ⎜ 0 ⎟ ⎝ ⎠ ) [ 360 e −100t ] 2 t = 8 ms ] 2 t = 8 ms 10 March 2006 = 72.68 W = - 36.34 W t = 8 ms t = ⎛ 90e −100t ∫ 3e −100t ′ dt ′ + 60e −100t ⎞ ⎜ ⎟ 0 ⎝ ⎠ = 27.63 W t = 8 ms PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
18. 18. Engineering Circuit Analysis, 7th Edition 18. Chapter Two Solutions 10 March 2006 (a) The short-circuit current is the value of the current at V = 0. Reading from the graph, this corresponds to approximately 3.0 A. (b) The open-circuit voltage is the value of the voltage at I = 0. Reading from the graph, this corresponds to roughly 0.4875 V, estimating the curve as hitting the x-axis 1 mm behind the 0.5 V mark. (c) We see that th e maximum current corres ponds to zero voltage , and likewise, the maximum voltage occu rs at zero curren t. The m aximum power point, therefore, occurs somewhere between these two points. By trial and error, Pmax is roughly (375 mV)(2.5 A) = 938 mW, or just under 1 W. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
19. 19. Engineering Circuit Analysis, 7th Edition 19. (a) Chapter Two Solutions 10 March 2006 P first 2 hours = ( 5 V )( 0.001 A ) = 5 mW P next 30 minutes = ( ? V )( 0 A ) = 0 mW P last 2 hours = ( 2 V )( −0.001 A ) = −2 mW (b) Energy = (5 V)(0.001 A)(2 hr)(60 min/ hr)(60 s/ min) = 36 J (c) 36 – (2)(0.001)(60)(60) = 21.6 J PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
20. 20. Engineering Circuit Analysis, 7th Edition 20. Chapter Two Solutions 10 March 2006 Note that in the table below, only th e –4-A sou rce and the –3-A source are actually “absorbing” power; the remaining sources are supplying power to the circuit. Source 2 V source 8 V source -4 A source 10 V source -3 A source Absorbed Power (2 V)(-2 A) (8 V)(-2 A) (10 V)[-(-4 A)] (10 V)(-5 A) (10 V)[-(-3 A)] The 5 powe r quantities sum to –4 – 16 + conservation of energy. Absorbed Power -4W - 16 W 40 W - 50 W 30 W 40 – 50 + 30 = 0, as de manded from PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
21. 21. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 10 March 2006 21. 20 A 32 V 8V –16 A 40 V –12 A 40 V P8V supplied = (8)(8) = 64 W (source of energy) P32V supplied = (32)(8) = 256 W (source of energy) P–16A supplied = (40)(–16) = –640 W P40V supplied = (40)(20) = 800 W P–12A supplied = (40)( –12) = Check: ∑ supplied power (source of energy) –480 W = 64 + 256 – 640 + 800 – 480 = 0 (ok) PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
22. 22. Engineering Circuit Analysis, 7th Edition 22. Chapter Two Solutions 10 March 2006 We are told that V x = 1 V, and from Fig. 2.33 w e see that the current flowing through the dependent source (and hence th rough each element of t he circuit) is 5V x = 5 A. We will co mpute absorbed power by using the current flowing into the po sitive reference terminal of the a ppropriate voltage (p assive sign conven tion), and we will compute supplied power by using the current flowing out of the pos itive reference terminal of the appropriate voltage. (a) The power absorbed by element “A” = (9 V)(5 A) = 45 W (b) The power supplied by the 1-V source = (1 V)(5 A) = 5 W, and the power supplied by the dependent source = (8 V)(5 A) = 40 W (c) The sum of the supplied power = 5 + 40 = 45 W The sum of the absorbed power is 45 W, so yes, the su m of the power supplied = the sum of the power absorbed, expect from the principle of conservation of energy. as we PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
23. 23. Engineering Circuit Analysis, 7th Edition 23. Chapter Two Solutions 10 March 2006 We are asked to determine the voltage vs, which is identical to the voltage labeled v1. The only remaining reference to v1 is in the expression for the current flowing through the dependent source, 5v1. This current is equal to –i2. Thus, 5 v1 = -i2 = - 5 mA Therefore v1 = -1 mV and so vs = v1 = -1 mV PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
24. 24. Engineering Circuit Analysis, 7th Edition 24. Chapter Two Solutions 10 March 2006 The voltage across the dependent source = v2 = –2ix = –2(–0.001) = 2 mV. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
25. 25. Engineering Circuit Analysis, 7th Edition 25. Chapter Two Solutions 10 March 2006 The battery delivers an energy of 460.8 W-hr over a period of 8 hrs. (a) The power delivered to the headlight is therefore (460.8 W-hr)/(8 hr) = 57.6 W (b) The current through the headlight is equal to the power it absorbs from the battery divided by the voltage at which the power is supplied, or I = (57.6 W)/(12 V) = 4.8 A PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
26. 26. Engineering Circuit Analysis, 7th Edition 26. Chapter Two Solutions 10 March 2006 The supply voltage is 110 V, and the m aximum dissipated power is 500 W. The fuse s are specified in te rms of current, so we need to determine the m aximum current th at can flow through the fuse. P=VI therefore Imax = Pmax/V = (500 W)/(110 V) = 4.545 A If we choose the 5-A fuse, it will allow up to (110 V)(5 A) = 550 W of power to be delivered to the application (we must assume here that the fuse absorbs zero power, a reasonable assumption in practice). This exceeds the specified maximum power. If we choose the 4.5-A fuse instead, we will hav e a m aximum current of 4.5 A. This leads to a maximum power of (110)(4.5) = 495 W delivered to the application. Although 495 W is less than the m aximum po wer allowed, this fuse will provid e adequate protection for the app lication circuitry. If a faul t occurs and the application circuitry attempts to draw too m uch power, 1000 W for example, the fuse will blow, no current will f low, and the application c ircuitry will be p rotected. However, if the application circuitry tries to draw its maximum rated power (500 W ), the fuse will also blow. In practice, m ost equipm ent will not draw its m aximum rated powe r continuously—although to be safe, we typically assume that it will. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
27. 27. Engineering Circuit Analysis, 7th Edition 27. (a) Chapter Two Solutions 5.556 mA imin = 5/ 1100 = (b) imax = 5/ 900 = 10 March 2006 4.545 mA p = v2 / R so pmin = 25/ 1100 = 22.73 mW pmax = 25/ 900 = 27.78 mW PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
28. 28. Engineering Circuit Analysis, 7th Edition 28. Chapter Two Solutions 10 March 2006 p = i2 R, so pmin = (0.002)2 (446.5) = 1.786 mW and (more relevant to our discussion) pmax = (0.002)2 (493.5) = 1.974 mW 1.974 mW would be a correct answer, although power ratings are typically expressed as integers, so 2 mW might be more appropriate. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
29. 29. Engineering Circuit Analysis, 7th Edition 29. (a) Chapter Two Solutions 10 March 2006 Pabs = i2R = [20e-12t] 2 (1200) μW = [20e-1.2] 2 (1200) μW = (b) 43.54 mW Pabs = v2/R = [40 cos 20t] 2 / 1200 W 2 = [40 cos 2] / 1200 W = keep in mind we are using radians 230.9 mW (c) = Pabs = v i= 8t 1.5 W 253.0 mW PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
30. 30. Engineering Circuit Analysis, 7th Edition 30. Chapter Two Solutions 10 March 2006 It’s probably best to begin this problem by sketching the voltage waveform: v (V) +10 40 60 t (ms) 20 -10 (a) vmax = +10 V (b) vavg = [(+10)(20×10-3) + (-10)(20×10-3)]/(40×10-3) = 0 (c) iavg = vavg /R = 0 (d) pabs (e) pabs max avg = = 2 vmax = (10)2 / 50 = 2 W R ⎤ 1 ⎡ (+10) 2 (−10) 2 ⋅ 20 + ⋅ 20⎥ = 2 W ⎢ R 40 ⎣ R ⎦ PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
31. 31. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 10 March 2006 31. Since we are inform ed that the same current must flow through each com ponent, we begin by defining a current I flowing out of the positive reference term inal of the voltage source. The power supplied by the voltage source is Vs I. The power absorbed by resistor R1 is I2R1. The power absorbed by resistor R2 is I2R2. Since we know that the total power supplied is equal to the total power absorbed, we may write: Vs I = I2R1 + I2R2 or Vs = I R1 + I R2 Vs = I (R1 + R2) By Ohm’s law, I = VR2 / R2 so that Vs = VR2 R2 (R1 + R2 ) Solving for VR2 we find VR2 = Vs R2 (R1 + R2 ) Q.E.D. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
32. 32. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 10 March 2006 32. (a) 6 5 4 c urrent (m A ) 3 2 1 0 -1 -2 -3 -4 -1.5 -1 -0.5 0 0.5 voltage (V ) 1 1.5 2 2.5 (b) W e see from our answer to part (a ) that this device has a reasonably linear characteristic (a not unreasonable degree of e xperimental error is evident in the data). Thus, we choose to estimate the resistance using the two extreme points: Reff = [(2.5 – (-1.5)]/[5.23 – (-3.19)] kΩ = 475 Ω Using the last two points instead, we find Reff = 469 Ω, so that we can state with some certainty at least that a reasonable estimate of the resistance is approximately 470 Ω. (c) 2 1.5 c urrent (m A ) 1 0.5 0 -0.5 -1 -1.5 -1.5 -1 -0.5 0 0.5 voltage (V ) 1 1.5 2 2.5 PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
33. 33. Engineering Circuit Analysis, 7th Edition Chapter Two Solutions 10 March 2006 Top Left Circuit: I = (5/10) mA = 0.5 mA, and P10k = V2/10 mW = 2.5 mW Top Right Circuit: 33. I = -(5/10) mA = -0.5 mA, and P10k = V2/10 mW = 2.5 mW Bottom Left Circuit: I = (-5/10) mA = -0.5 mA, and P10k = V2/10 mW = 2.5 mW Bottom Right Circuit: I = -(-5/10) mA = 0.5 mA, and P10k = V2/10 mW = 2.5 mW PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
34. 34. Engineering Circuit Analysis, 7th Edition 34. The Chapter Two Solutions 10 March 2006 voltage vout is given by vout = -10-3 vπ (1000) = - vπ Since vπ = vs = 0.01 cos 1000t V, we find that vout = - vπ = -0.01 cos 1000t V PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
35. 35. Engineering Circuit Analysis, 7th Edition 35. Chapter Two Solutions 10 March 2006 vout = -vπ = -vS = -2sin 5t V vout (t = 0) = 0 V vout (t = 0.324 s) = -2sin (1.57) = -2 V (use care to em ploy r adian m ode on your calculator or convert 1.57 radians to degrees) PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
36. 36. Engineering Circuit Analysis, 7th Edition 36. Chapter Two Solutions 10 March 2006 18 AWG wire has a resistance of 6.39 Ω / 1000 ft. Thus, we require 1000 (53) / 6.39 = 8294 ft of wire. (Or 1.57 miles. Or, 2.53 km). PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
37. 37. Engineering Circuit Analysis, 7th Edition 37. tem Chapter Two Solutions 10 March 2006 We need to create a 47 0-Ω resistor from 28 AWG wire , knowing that the am bient perature is 108oF, or 42.22oC. Referring to Table 2.3, 28 AWG wire is 65.3 m Ω/ft at 20 oC, and using the equation provided we compute R2/R1 = (234.5 + T2)/(234.5 + T1) = (234.5 + 42.22)/(234.5 + 20) = 1.087 We thus find that 28 AWG wire is (1.087)(65.3) = 71.0 mΩ/ft. Thus, to repair the transmitter we will need (470 Ω)/(71.0 × 10-3 Ω/ft) = 6620 ft (1.25 miles, or 2.02 km). Note: This seems like a lot of wire to be washing up on shore. We may find we don’t have enough. In that case, perhaps we shoul d take our cue from Eq. [6], and try to squash a piece of the wire flat so that it has a very small cross-sectional area….. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
38. 38. Engineering Circuit Analysis, 7th Edition 38. Chapter Two Solutions 10 March 2006 We are given that the conductivity σ of copper is 5.8×107 S/m. (a) 50 ft of #18 (18 AWG) copper wire, which has a diameter of 1.024 mm, will have a resistance of l/(σ A) ohms, where A = the cross-sectional area and l = 50 ft. Converting the dimensional quantities to meters, l = (50 ft)(12 in/ft)(2.54 cm/in)(1 m/100 cm) = 15.24 m and r = 0.5(1.024 mm)(1 m/1000 mm) = 5.12×10-4 m so that A = π r2 = π (5.12×10-4 m)2 = 8.236×10-7 m2 Thus, R = (15.24 m)/[( 5.8×107)( 8.236×10-7)] = 319.0 mΩ (b) We assume that the conductivity value specified also holds true at 50oC. The cross-sectional area of the foil is A = (33 μm)(500 μm)(1 m/106 μm)( 1 m/106 μm) = 1.65×10-8 m2 So that R = (15 cm)(1 m/100 cm)/[( 5.8×107)( 1.65×10-8)] = 156.7 mΩ A 3-A current flowing through this copper in the direction specified would lead to the dissipation of I2R = (3)2 (156.7) mW = 1.410 W PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
39. 39. Engineering Circuit Analysis, 7th Edition 39. Chapter Two Solutions 10 March 2006 Since R = ρ l / A, it follows that ρ = R A/ l . From Table 2.4, we see that 28 AWG soft copper wire (cross-sectional area = 0.080 4 mm2) is 65.3 Ω per 1000 ft. Thus, R = 65.3 Ω. l = (1000 ft)(12 in/ft)(2.54 cm/in)(10 mm/cm) = 304,800 mm. A = 0.0804 mm2. Thus, ρ = (65.3)(0.0804)/304800 = 17.23 μΩ/ mm or ρ = 1.723 μΩ.cm which is in fact consistent with the representative data for copper in Table 2.3. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
40. 40. Engineering Circuit Analysis, 7th Edition 40. Chapter Two Solutions 10 March 2006 (a) From the text, (1) Zener diodes, (2) Fuses, and (3) Incandescent (as opposed to fluorescent) light bulbs This last on e requires a few facts to be put together. We have st ated that temperature can affect resistance—in other words, if the temperature changes during operation, the resistance will not rem ain constant and hence nonlinear behavior will be observed. Most discrete resistors are rated for up to a sp ecific power in o rder to ensure th at temperature variation during operation will no t significantly change th e res istance value. Light bulbs, however, become rather warm when operating and can experience a significant change in resistance. (b) The energy is dissipated by the resistor, converted to heat which is transferred to the air surrounding the resistor. The resistor is unable to store the energy itself. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
41. 41. Engineering Circuit Analysis, 7th Edition 41. Chapter Two Solutions 10 March 2006 The quoted resistivity ρ of B33 copper is 1.7654 μΩ.cm. A = πr2 = π(10–3)2 = 10–6π m2. l = 100 m. (1.7654 ×10 Thus, R = ρ l / A = −6 ) Ωcm (1 m/100 cm )(100 m ) 10−6 π = 0.5619 Ω And P = I2R = (1.5)2 (0.5619) = 1.264 W. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
42. 42. Engineering Circuit Analysis, 7th Edition 42. Chapter Two Solutions 10 March 2006 We know that for any wire of cross-sectional area A and length l , the resistan ce is given by R = ρ l / A. If we keep ρ fixed by choosing a material, and A fixed by choosing a wire gauge (e.g. 28 AWG), changing l will change the resistance of our “device.” A simple variable resistor concept, then: Leads to connect to circuit Copper wire Rotating sh ort wire de termines length of long wire used in circuit. But this is s omewhat impractical, as the l eads may turn out to have alm ost the sam e resistance unless we have a very long wi re, which can also be im practical. One improvement would be to replace the coppe r wire shown with a coil of insulated copper wire. A s mall amount of insulation would then need to be removed from where the moveable wire touches the coil so that electrical connection could be made. PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
43. 43. Engineering Circuit Analysis, 7th Edition 43. Chapter Two Solutions 10 March 2006 (a) We need to plot the negative and positive voltage ranges separately, as the positive voltage range is, after all, exponential! x 10 -6 10 16 -4 14 12 10 -5 c urrent (A ) c urrent (A) 10 8 6 10 -6 4 10 2 -7 0 -2 -0.7 10 -0.6 -0.5 -0.4 -0.3 -0.2 voltage (V ) -0.1 0 -8 0.1 0 (b) To dete rmine the resist ance of the device at corresponding current: 0.01 0.02 0.03 0.04 voltage (V) V = 550 mV, we com 0.05 0.06 pute the I = 10-9 [e39(0.55) – 1] = 2.068 A Thus, R(0.55 V) = 0.55/2.068 = 266 mΩ (c) R = 1 Ω corresponds to V = I. Thus, we need to solve the transcendental equation I = 10-9 [e39I – 1] Using a scientific calculator or the tried-and-true trial and error approach, we find that I = 514.3 mA PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission. 0.07
44. 44. Engineering Circuit Analysis, 7th Edition 44. Chapter Two Solutions 10 March 2006 We require a 10- Ω resistor, and are told it is f or a portable application, implying that size, weight or both would be im portant to consider when selecting a wire gauge. W e have 10,000 ft of each of the gaug es listed in Table 2.3 w ith which to work. Quick inspection o f the values listed e liminates 2, 4 a nd 6 AW G w ire as the ir respec tive resistances are too low for only 10,000 ft of wire. Using 12-AWG wire would require (10 Ω) / (1.59 mΩ/ft) = 6290 ft. Using 28-AWG wire, the narrowest available, would require (10 Ω) / (65.3 mΩ/ft) = 153 ft. Would the 28-AW G wire weight less? Again referring to T able 2.3, we see that the cross-sectional area of 28-AWG wire is 0.0804 mm 2, and that of 12-AWG wire is 3.31 mm2. The volume of 12-AWG wire required is therefore 6345900 mm 3, and that of 28-AWG wire required is only 3750 mm3. The best (but not the only) choice for a portable application is clear: 28-AWG wire! PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
45. 45. Engineering Circuit Analysis, 7th Edition 45. cm Chapter Two Solutions 10 March 2006 Our target is a 100-Ω resistor. We see from the plot that at ND = 1015 cm-3, μn ~ 2x103 2 /V-s, yielding a resistivity of 3.121 Ω-cm. At ND = 1018 cm-3, μn ~ 230 cm2/ V-s, yielding a resistivity of 0.02714 Ω-cm. Thus, we s ee that the lower doping level cl early provides m aterial with higher resistivity, requiring less of the available area on the silicon wafer. Since R = ρL/A, where we know R = 100 Ω and ρ = 3.121 Ω-cm for a phosphorus concentration of 1015 cm-3, we need only define the resistor geom etry to complete the design. We choose a geometry as shown in the figure; our contact area is arbitrarily chosen as 100 μm by 250 μm, so that only the length L remains to be specified. Solving, L= R ρ A= (100 Ω)(100 μ )(250 μ ) m m = 80.1 μ m 4 ( 3.121 Ω cm ) 10 μ m/cm ( ) Design summary (one possibility): Contact ND = 1015 cm-3 L = 80.1 μm width 100 μm = (Note: this is som ewhat atypical; in the semiconductor industry contacts are typically made to the top and/o r bottom surface of a wafer. So, there’s more than one solu tion based on geometry as well as doping level.) 100 μm Wafer surface 250 μm contact 80.1 μm contact PROPRIETARY MATERIAL . © 2007 Th e McGraw-Hill Companies, Inc. Lim ited distr ibution perm itted onl y to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
46. 46. Engineering Circuit Analysis, 7th Edition Chapter Three Solutions 10 March 2006 1. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
47. 47. Engineering Circuit Analysis, 7th Edition 2. Chapter Three Solutions 10 March 2006 (a) six nodes; (b) nine branches. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
48. 48. Engineering Circuit Analysis, 7th Edition 3. Chapter Three Solutions 10 March 2006 (a) Four nodes; (b) five branches; (c) path, yes – loop, no. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
49. 49. Engineering Circuit Analysis, 7th Edition 4. Chapter Three Solutions 10 March 2006 (a) Five nodes; (b) seven branches; (c) path, yes – loop, no. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
50. 50. Engineering Circuit Analysis, 7th Edition 5. Chapter Three Solutions 10 March 2006 (a) The number of nodes remains the same – four (4). (b) The number of nodes is increased by one – to five (5). (c) i) ii) iii) iv) v) YES NO YES NO NO – does not return to starting point – does not return to starting point – point B is crossed twice PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
51. 51. Engineering Circuit Analysis, 7th Edition 6. (a) By KCL at the bottom node: So iZ = 9 A. Chapter Three Solutions 10 March 2006 2 – 3 + iZ – 5 – 3 = 0 (b) If the left-most resistor has a value of 1 Ω, then 3 V appears across the parallel network (the ‘+’ reference terminal being the bottom node) Thus, the value of the other resistor is given by R= 3 = 600 mΩ . −(−5) PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
52. 52. Engineering Circuit Analysis, 7th Edition 7. Chapter Three Solutions 10 March 2006 (a) 3 A; (b) –3 A; (c) 0. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
53. 53. Engineering Circuit Analysis, 7th Edition 8. Chapter Three Solutions 10 March 2006 By KCL, we may write: 5 + iy + iz = 3 + ix (a) ix = 2 + iy + iz = 2 + 2 + 0 = 4 A (b) iy = 3 + ix – 5 – iz iy = –2 + 2 – 2 iy Thus, we find that iy = 0. (c) 5 + iy + iz = 3 + ix → 5 + ix + ix = 3 + ix so ix = 3 – 5 = -2A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
54. 54. Engineering Circuit Analysis, 7th Edition 9. Chapter Three Solutions 10 March 2006 Focusing our attention on the bottom left node, we see that ix = 1 A. Focusing our attention next on the top right node, we see that iy = 5 A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
55. 55. Engineering Circuit Analysis, 7th Edition 10. Chapter Three Solutions 10 March 2006 We obtain the current each bulb draws by dividing its power rating by the operating voltage (115 V): I100W = 100/115 = 896.6 mA I60W = 60/115 = 521.7 mA I40W = 347.8 mA Thus, the total current draw is 1.739 A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
56. 56. Engineering Circuit Analysis, 7th Edition 11. Chapter Three Solutions 10 March 2006 The DMM is connected in parallel with the 3 load resistors, across which develops the voltage we wish to measure. If the DMM appears as a short, then all 5 A flows through the DMM, and none through the resistors, resulting in a (false) reading of 0 V for the circuit undergoing testing. If, instead, the DMM has an infinite internal resistance, then no current is shunted away from the load resistors of the circuit, and a true voltage reading results. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
57. 57. Engineering Circuit Analysis, 7th Edition 12. Chapter Three Solutions 10 March 2006 In either case, a bulb failure will adversely affect the sign. Still, in the parallel-connected case, at least 10 (up to 11) of the other characters will be lit, so the sign could be read and customers will know the restaurant is open for business. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
58. 58. Engineering Circuit Analysis, 7th Edition 13. Chapter Three Solutions 10 March 2006 (a) vy = 1(3vx + iz) vx = 5 V and given that iz = –3 A, we find that vy = 3(5) – 3 = 12 V (b) vy = 1(3vx + iz) = –6 = 3vx + 0.5 Solving, we find that vx = (–6 – 0.5)/3 = –2.167 V. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
59. 59. Engineering Circuit Analysis, 7th Edition 14. Chapter Three Solutions 10 March 2006 (a) ix = v1/10 + v1/10 = 5 2v1 = 50 so v1 = 25 V. By Ohm’s law, we see that iy = v2/10 also, using Ohm’s law in combination with KCL, we may write ix = v2/10 + v2/10 = iy + iy = 5 A Thus, iy = 2.5 A. (b) From part (a), ix = 2 v1/ 10. Substituting the new value for v1, we find that ix = 6/10 = 600 mA. Since we have found that iy = 0.5 ix, iy = 300 mA. (c) no value – this is impossible. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
60. 60. Engineering Circuit Analysis, 7th Edition 15. Chapter Three Solutions 10 March 2006 We begin by making use of the information given regarding the power generated by the 5-A and the 40-V sources. The 5-A source supplies 100 W, so it must therefore have a terminal voltage of 20 V. The 40-V source supplies 500 W, so it must therefore provide a current IX of 12.5 A. (1) By KVL, –40 + (–110) + R(5) – 20 = 0 Thus, R = 34 Ω. (2) By KVL, -VG – (-110) + 40 = 0 So VG = 150 V Now that we know the voltage across the unknown conductance G, we need only to find the current flowing through it to find its value by making use of Ohm’s law. KCL provides us with the means to find this current: The current flowing into the “+” terminal of the –110-V source is 12.5 + 6 = 18.5 A. Then, Ix = 18.5 – 5 = 13.5 A By Ohm’s law, I x = G · VG So G = 13.5/ 150 or G = 90 mS PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
61. 61. Engineering Circuit Analysis, 7th Edition 16. Chapter Three Solutions 10 March 2006 (a) -1 + 2 + 10i – 3.5 + 10i = 0 Solving, i = 125 mA (b) +10 + 1i - 2 + 2i + 2 – 6 + i = 0 Solving, we find that 4i = -4 or i = - 1 A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
62. 62. Engineering Circuit Analysis, 7th Edition 17. Chapter Three Solutions 10 March 2006 Circuit I. Starting at the bottom node and proceeding clockwise, we can write the KVL equation +7 – 5 – 2 – 1(i) = 0 Which results in i = 0. Circuit II. Again starting with the bottom node and proceeding in a clockwise direction, we write the KVL equation -9 +4i + 4i = 0 (no current flows through either the -3 V source or the 2 Ω resistor) Solving, we find that i = 9/8 A = 1.125 A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
63. 63. Engineering Circuit Analysis, 7th Edition 18. Chapter Three Solutions 10 March 2006 Begin by defining a clockwise current i. -vS + v1 + v2 = 0 and hence i = so vS = v1 + v2 = i(R1 + R2) vS . R1 + R2 Thus, v1 = R1i = R1 R2 vS and v2 = R2i = vS . R1 + R2 R1 + R2 Q.E.D. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
64. 64. Engineering Circuit Analysis, 7th Edition 19. Chapter Three Solutions 10 March 2006 Given: (1) Vd = 0 and (2) no current flows into either terminal of Vd. Calculate Vout by writing two KVL equations. Begin by defining current i1 flowing right through the 100 Ω resistor, and i2 flowing right through the 470 Ω resistor. -5 + 100i1 + Vd = 0 [1] -5 + 100i1 + 470i2 + Vout = 0 [2] Making use of the fact that in this case Vd = 0, we find that i1 = 5/100 A. Making use of the fact that no current flows into the input terminals of the op amp, i1 = i2. Thus, Eq. [2] reduces to -5 + 570(5/100) + Vout = 0 or Vout = -23.5 V (hence, the circuit is acting as a voltage amplifier.) PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
65. 65. Engineering Circuit Analysis, 7th Edition 20. Chapter Three Solutions 10 March 2006 (a) By KVL, -2 + vx + 8 = 0 so that vx = -6 V. (b) By KCL at the top left node, iin = 1 + IS + vx/4 – 6 or iin = 23 A (c) By KCL at the top right node, IS + 4 vx = 4 - vx/4 So IS = 29.5 A. (d) The power provided by the dependent source is 8(4vx) = -192 W. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
66. 66. Engineering Circuit Analysis, 7th Edition 21. (a) Working from left to right, v1 = 60 V v2 = 60 V i2 = 60/20 = 3 A i4 = v1/4 = 60/4 = 15 A v3 = 5i2 = 15 V By KVL, -60 + v3 + v5 = 0 v5 = 60 – 15 = 45 V v4 = v5 = 45 Chapter Three Solutions v1 = 60 V v2 = 60 V v3 = 15 V v4 = 45 V v5 = 45 V 10 March 2006 i1 = 27 A i2 = 3 A i3 = 24 A i4 = 15 A i5 = 9 A i5 = v5/5 = 45/5 = 9 A i3 = i4 + i5 = 15 + 9 = 24 A i1 = i2 + i3 = 3 + 24 = 27 (b) It is now a simple matter to compute the power absorbed by each element: p1 p2 p3 p4 p5 = -v1i1 = v2i2 = v3i3 = v4i4 = v5i5 = -(60)(27) = (60)(3) = (15)(24) = (45)(15) = (45)(9) = -1.62 kW = 180 W = 360 W = 675 W = 405 W and it is a simple matter to check that these values indeed sum to zero as they should. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
67. 67. Engineering Circuit Analysis, 7th Edition 22. Chapter Three Solutions 10 March 2006 Refer to the labeled diagram below. Beginning from the left, we find p20V = -(20)(4) = -80 W v1.5 = 4(1.5) = 6 V therefore p1.5 = (v1.5)2/ 1.5 = 24 W. v14 = 20 – v1.5 = 20 – 6 = 14 V therefore p14 = 142/ 14 = 14 W. i2 = v2/2 = v1.5/1.5 – v14/14 = 6/1.5 – 14/14 = 3 A Therefore v2 = 2(3) = 6 V and p2 = 62/2 = 18 W. v4 = v14 – v2 = 14 – 6 = 8 V therefore p4 = 82/4 = 16 W i2.5 = v2.5/ 2.5 = v2/2 – v4/4 = 3 – 2 = 1 A Therefore v2.5 = (2.5)(1) = 2.5 V and so p2.5 = (2.5)2/2.5 = 2.5 W. I2.5 = - IS, thefore IS = -1 A. KVL allows us to write -v4 + v2.5 + vIS = 0 so VIS = v4 – v2.5 = 8 – 2.5 = 5.5 V and pIS = -VIS IS = 5.5 W. A quick check assures us that these power quantities sum to zero. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
68. 68. Engineering Circuit Analysis, 7th Edition 23. Chapter Three Solutions 10 March 2006 Sketching the circuit as described, (a) v14 = 0. v13 = v43 v23 = -v12 – v34 = -12 + 8 v24 = v23 + v34 = -4 – 8 = 8V = -4 V = -12 V (b) v14 = 6 V. v13 = v14 + v43 = 6 + 8 v23 = v13 – v12 = 14 – 12 v24 = v23 + v34 = 2 – 8 = 14 V = 2V = -6 V (c) v14 = -6 V. v13 = v14 + v43 = -6 + 8 v23 = v13 – v12 = 2 – 12 v24 = v23 + v34 = -10 – 8 = 2V = -10 V = -18 V PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
69. 69. Engineering Circuit Analysis, 7th Edition 24. Chapter Three Solutions 10 March 2006 (a) By KVL, -12 + 5000ID + VDS + 2000ID = 0 Therefore, VDS = 12 – 7(1.5) = 1.5 V. (b) By KVL, - VG + VGS + 2000ID = 0 Therefore, VGS = VG – 2(2) = -1 V. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
70. 70. Engineering Circuit Analysis, 7th Edition 25. Chapter Three Solutions 10 March 2006 Applying KVL around this series circuit, -120 + 30ix + 40ix + 20ix + vx + 20 + 10ix = 0 where vx is defined across the unknown element X, with the “+” reference on top. Simplifying, we find that 100ix + vx = 100 To solve further we require specific information about the element X and its properties. (a) if X is a 100-Ω resistor, vx = 100ix so we find that 100 ix + 100 ix = 100. Thus ix = 500 mA and px = vx ix = 25 W. (b) If X is a 40-V independent voltage source such that vx = 40 V, we find that ix = (100 – 40) / 100 = 600 mA and px = vx ix = 24 W (c) If X is a dependent voltage source such that vx = 25ix, ix = 100/125 = 800 mA and px = vx ix = 16 W. (d) If X is a dependent voltage source so that vx = 0.8v1, where v1 = 40ix, we have 100 ix + 0.8(40ix) = 100 px = vx ix = 0.8(40)(0.7576)2 = 18.37 W. or ix = 100/132 = 757.6 mA and (e) If X is a 2-A independent current source, arrow up, 100(-2) + vx = 100 so that vx = 100 + 200 = 300 V and px = vx ix = -600 W PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
71. 71. Engineering Circuit Analysis, 7th Edition 26. Chapter Three Solutions 10 March 2006 (a) We first apply KVL: -20 + 10i1 + 90 + 40i1 + 2v2 = 0 where v2 = 10i1. Substituting, 70 + 70 i1 = 0 or i1= -1 A. (b) Applying KVL, -20 + 10i1 + 90 + 40i1 + 1.5v3 = 0 [1] where v3 = -90 – 10i1 + 20 = -70 – 10 i1 alternatively, we could write v3 = 40i1 + 1.5v3 = -80i1 Using either expression in Eq. [1], we find i1 = 1 A. (c) Applying KVL, -20 + 10i1 + 90 + 40i1 - 15 i1 = 0 Solving, i1 = - 2A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
72. 72. Engineering Circuit Analysis, 7th Edition 27. Chapter Three Solutions 10 March 2006 Applying KVL, we find that -20 + 10i1 + 90 + 40i1 + 1.8v3 = 0 [1] Also, KVL allows us to write v3 = 40i1 + 1.8v3 v3 = -50i1 So that we may write Eq. [1] as 50i1 – 1.8(50)i1 = -70 or i1 = -70/-40 = 1.75 A. Since v3 = -50i1 = -87.5 V, no further information is required to determine its value. The 90-V source is absorbing (90)(i1) = 157.5 W of power and the dependent source is absorbing (1.8v3)(i1) = -275.6 W of power. Therefore, none of the conditions specified in (a) to (d) can be met by this circuit. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
73. 73. Engineering Circuit Analysis, 7th Edition 28. Chapter Three Solutions 10 March 2006 (a) Define the charging current i as flowing clockwise in the circuit provided. By application of KVL, -13 + 0.02i + Ri + 0.035i + 10.5 = 0 We know that we need a current i = 4 A, so we may calculate the necessary resistance R = [13 – 10.5 – 0.055(4)]/ 4 = 570 mΩ (b) The total power delivered to the battery consists of the power absorbed by the 0.035-Ω resistance (0.035i2), and the power absorbed by the 10.5-V ideal battery (10.5i). Thus, we need to solve the quadratic equation 0.035i2 + 10.5i = 25 which has the solutions i = -302.4 A and i = 2.362 A. In order to determine which of these two values should be used, we must recall that the idea is to charge the battery, implying that it is absorbing power, or that i as defined is positive. Thus, we choose i = 2.362 A, and, making use of the expression developed in part (a), we find that R = [13 – 10.5 – 0.055(2.362)]/ 2.362 = 1.003 Ω (c) To obtain a voltage of 11 V across the battery, we apply KVL: 0.035i + 10.5 = 11 so that i = 14.29 A From part (a), this means we need R = [13 – 10.5 – 0.055(14.29)]/ 14.29 = 119.9 mΩ PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
74. 74. Engineering Circuit Analysis, 7th Edition 29. Chapter Three Solutions 10 March 2006 Drawing the circuit described, we also define a clockwise current i. By KVL, we find that -13 + (0.02 + 0.5 – 0.05)i + 0.035i + 10.5 = 0 or that i = (13 – 10.5)/0.505 = 4.951 A and Vbattery = 13 – (0.02 + 0.5)i = 10.43 V. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
75. 75. Engineering Circuit Analysis, 7th Edition 30. Chapter Three Solutions 10 March 2006 Applying KVL about this simple loop circuit (the dependent sources are still linear elements, by the way, as they depend only upon a sum of voltages) -40 + (5 + 25 + 20)i – (2v3 + v2) + (4v1 – v2) = 0 [1] where we have defined i to be flowing in the clockwise direction, and v1 = 5i, v2 = 25i, and v3 = 20i. Performing the necessary substition, Eq. [1] becomes 50i - (40i + 25i) + (20i – 25i) = 40 so that i = 40/-20 = -2 A Computing the absorbed power is now a straightforward matter: p40V p5Ω p25Ω p20Ω pdepsrc1 pdepsrc2 = (40)(-i) = 5i2 = 25i2 = 20i2 = (2v3 + v2)(-i) = (40i + 25i) = (4v1 - v2)(-i) = (20i - 25i) = 80 W = 20 W = 100 W = 80 W = -260 W = -20 W and we can easily verify that these quantities indeed sum to zero as expected. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
76. 76. Engineering Circuit Analysis, 7th Edition 31. Chapter Three Solutions 10 March 2006 We begin by defining a clockwise current i. (a) i = 12/(40 + R) mA, with R expressed in kΩ. We want i2 · 25 = 2 2 or ⎛ 12 ⎞ ⎜ ⎟ ⋅ 25 = 2 ⎝ 40 + R ⎠ Rearranging, we find a quadratic expression involving R: R2 + 80R – 200 = 0 which has the solutions R = -82.43 kΩ and R = 2.426 kΩ. Only the latter is a physical solution, so R = 2.426 kΩ. (b) We require i · 12 = 3.6 or i = 0.3 mA From the circuit, we also see that i = 12/(15 + R + 25) mA. Substituting the desired value for i, we find that the required value of R is R = 0. (c) PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
77. 77. Engineering Circuit Analysis, 7th Edition 32. Chapter Three Solutions 10 March 2006 By KVL, –12 + (1 + 2.3 + Rwire segment) i = 0 The wire segment is a 3000–ft section of 28–AWG solid copper wire. Using Table 2.3, we compute its resistance as (16.2 mΩ/ft)(3000 ft) = 48.6 Ω which is certainly not negligible compared to the other resistances in the circuit! Thus, i = 12/(1 + 2.3 + 48.6) = 231.2 mA PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
78. 78. Engineering Circuit Analysis, 7th Edition 33. Chapter Three Solutions 10 March 2006 We can apply Ohm’s law to find an expression for vo: vo = 1000(–gm vπ) We do not have a value for vπ, but KVL will allow us to express that in terms of vo, which we do know: –10×10–3 cos 5t + (300 + 50×103) i = 0 where i is defined as flowing clockwise. Thus, vπ = 50×103 i = 50×103 (10×10–3 cos 5t) / (300 + 50×103) = 9.940×10–3 cos 5t V and we by substitution we find that vo = 1000(–25×10–3)( 9.940×10–3 cos 5t ) = –248.5 cos 5t mV PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
79. 79. Engineering Circuit Analysis, 7th Edition 34. Chapter Three Solutions 10 March 2006 By KVL, we find that –3 + 100 ID + VD = 0 –3 Substituting ID = 3×10–6(eVD / 27×10 – 1), we find that –3 –3 + 300×10–6(eVD / 27×10 – 1) + VD = 0 This is a transcendental equation. Using a scientific calculator or a numerical software package such as MATLAB®, we find VD = 246.4 mV Let’s assume such software-based assistance is unavailable. In that case, we need to “guess” a value for VD, substitute it into the right hand side of our equation, and see how close the result is to the left hand side (in this case, zero). GUESS 0 1 0.5 0.25 0.245 0.248 0.246 RESULT –3 3.648×1012 3.308×104 0.4001 –0.1375 0.1732 –0.0377 oops better At this point, the error is getting much smaller, and our confidence is increasing as to the value of VD. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
80. 80. Engineering Circuit Analysis, 7th Edition 35. Chapter Three Solutions 10 March 2006 Define a voltage vx, “+” reference on the right, across the dependent current source. Note that in fact vx appears across each of the four elements. We first convert the 10 mS conductance into a 100–Ω resistor, and the 40–mS conductance into a 25–Ω resistor. (a) Applying KCL, we sum the currents flowing into the right–hand node: 5 – vx / 100 – vx / 25 + 0.8 ix = 0 [1] This represents one equation in two unknowns. A second equation to introduce at this point is ix = vx /25 so that Eq. [1] becomes 5 – vx / 100 – vx / 25 + 0.8 (vx / 25) = 0 Solving for vx, we find vx = 277.8 V. It is a simple matter now to compute the power absorbed by each element: P5A = –5 vx = –1.389 kW P100Ω = (vx)2 / 100 = 771.7 W P25Ω 2 = 3.087 kW Pdep = (vx) / 25 2 = –vx(0.8 ix) = –0.8 (vx) / 25 = –2.470 kW A quick check assures us that the calculated values sum to zero, as they should. (b) Again summing the currents into the right–hand node, 5 – vx / 100 – vx / 25 + 0.8 iy = 0 [2] where iy = 5 – vx/100 Thus, Eq. [2] becomes 5 – vx / 100 – vx / 25 + 0.8(5) – 0.8 (iy) / 100 = 0 Solving, we find that vx x = 155.2 V and iy = 3.448 A So that P5A = –5 vx = –776.0 W P100Ω = (vx)2 / 100 = 240.9 W P25Ω 2 = (vx) / 25 = 963.5 W Pdep = –vx(0.8 iy) = –428.1 W A quick check shows us that the calculated values sum to 0.3, which is reasonably close to zero compared to the size of the terms (small roundoff errors accumulated). PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
81. 81. Engineering Circuit Analysis, 7th Edition 36. Chapter Three Solutions 10 March 2006 Define a voltage v with the “+” reference at the top node. Applying KCL and summing the currents flowing out of the top node, v/5,000 + 4×10–3 + 3i1 + v/20,000 = 0 [1] This, unfortunately, is one equation in two unknowns, necessitating the search for a second suitable equation. Returning to the circuit diagram, we observe that i1 or i1 = = 3 i1 + v/2,000 –v/40,000 [2] Upon substituting Eq. [2] into Eq. [1], Eq. [1] becomes, v/5,000 + 4×10–3 – 3v/40,000 + v/20,000 = 0 Solving, we find that v = –22.86 V and i1 = 571.4 μA Since ix = i1, we find that ix = 571.4 μA. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
82. 82. Engineering Circuit Analysis, 7th Edition 37. Chapter Three Solutions 10 March 2006 Define a voltage vx with its “+” reference at the center node. Applying KCL and summing the currents into the center node, 8 – vx /6 + 7 – vx /12 – vx /4 = 0 Solving, vx = 30 V. It is now a straightforward matter to compute the power absorbed by each element: P8A = –8 vx 2 = –240 W P6Ω = (vx) / 6 = P8A = –7 vx = –210 W P12Ω P4Ω 150 W 2 = 75 W 2 = 225 W = (vx) / 12 = (vx) / 4 and a quick check verifies that the computed quantities sum to zero, as expected. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
83. 83. Engineering Circuit Analysis, 7th Edition 38. Chapter Three Solutions 10 March 2006 (a) Define a voltage v across the 1–kΩ resistor with the “+” reference at the top node. Applying KCL at this top node, we find that 80×10–3 – 30×10–3 = v/1000 + v/4000 Solving, v = (50×10–3)(4×106 / 5×103) = 40 V P4kΩ = v2/4000 = 400 mW and (b) Once again, we first define a voltage v across the 1–kΩ resistor with the “+” reference at the top node. Applying KCL at this top node, we find that 80×10–3 – 30×10–3 – 20×10–3 = v/1000 Solving, v = 30 V P20mA = v · 20×10–3 = 600 mW and (c) Once again, we first define a voltage v across the 1–kΩ resistor with the “+” reference at the top node. Applying KCL at this top node, we find that 80×10–3 – 30×10–3 – 2ix = v/1000 where ix = v/1000 so that 80×10–3 – 30×10–3 = 2v/1000 + v/1000 and v = 50×10–3 (1000)/3 = 16.67 V Thus, Pdep = v · 2ix = 555.8 mW (d) We note that ix = 60/1000 = 60 mA. KCL stipulates that (viewing currents into and out of the top node) 80 – 30 + is = ix = 60 Thus, is = 10 mA and P60V = 60(–10) mW = –600 mW PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
84. 84. Engineering Circuit Analysis, 7th Edition 39. Chapter Three Solutions 10 March 2006 (a) To cancel out the effects of both the 80-mA and 30-mA sources, iS must be set to iS = –50 mA. (b) Define a current is flowing out of the “+” reference terminal of the independent voltage source. Interpret “no power” to mean “zero power.” Summing the currents flowing into the top node and invoking KCL, we find that 80×10-3 - 30×10-3 - vS/1×103 + iS = 0 Simplifying slightly, this becomes 50 - vS + 103 iS = 0 [1] We are seeking a value for vS such that vS · iS = 0. Clearly, setting vS = 0 will achieve this. From Eq. [1], we also see that setting vS = 50 V will work as well. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
85. 85. Engineering Circuit Analysis, 7th Edition 40. Chapter Three Solutions 10 March 2006 Define a voltage v9 across the 9-Ω resistor, with the “+” reference at the top node. (a) Summing the currents into the right-hand node and applying KCL, 5 + 7 = v9 / 3 + v9 / 9 Solving, we find that v9 = 27 V. Since ix = v9 / 9, ix = 3 A. (b) Again, we apply KCL, this time to the top left node: 2 – v8 / 8 + 2ix – 5 = 0 Since we know from part (a) that ix = 3 A, we may calculate v8 = 24 V. (c) p5A = (v9 – v8) · 5 = 15 W. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
86. 86. Engineering Circuit Analysis, 7th Edition 41. Chapter Three Solutions 10 March 2006 Define a voltage vx across the 5-A source, with the “+” reference on top. Applying KCL at the top node then yields 5 + 5v1 - vx/ (1 + 2) – vx/ 5 = 0 [1] where v1 = 2[vx /(1 + 2)] = 2 vx / 3. Thus, Eq. [1] becomes 5 + 5(2 vx / 3) – vx / 3 – vx / 5 = 0 or 75 + 50 vx – 5 vx – 3 vx = 0, which, upon solving, yields vx = -1.786 V. The power absorbed by the 5-Ω resistor is then simply (vx)2/5 = 638.0 mW. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
87. 87. Engineering Circuit Analysis, 7th Edition 42. Chapter Three Solutions 10 March 2006 Despite the way it may appear at first glance, this is actually a simple node-pair circuit. Define a voltage v across the elements, with the “+” reference at the top node. Summing the currents leaving the top node and applying KCL, we find that 2 + 6 + 3 + v/5 + v/5 + v/5 = 0 or v = -55/3 = -18.33 V. The power supplied by each source is then computed as: p2A = -v(2) = 36.67 W p6A = -v(6) = 110 W p3A = -v(3) = 55 W The power absorbed by each resistor is simply v2/5 = 67.22 W for a total of 201.67 W, which is the total power supplied by all sources. If instead we want the “power supplied” by the resistors, we multiply by -1 to obtain -201.67 W. Thus, the sum of the supplied power of each circuit element is zero, as it should be. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
88. 88. Engineering Circuit Analysis, 7th Edition 43. Chapter Three Solutions 10 March 2006 Defining a voltage Vx across the 10-A source with the “+” reference at the top node, KCL tells us that 10 = 5 + I1Ω, where I1Ω is defined flowing downward through the 1-Ω resistor. Solving, we find that I1Ω = 5 A, so that Vx = (1)(5) = 5 V. So, we need to solve Vx = 5 = 5(0.5 + Rsegment) with Rsegment = 500 mΩ. From Table 2.3, we see that 28-AWG solid copper wire has a resistance of 65.3 mΩ/ft. Thus, the total number of miles needed of the wire is 500 mΩ (65.3 mΩ/ft)(5280 ft/mi) = 1.450 × 10-3 miles PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
89. 89. Engineering Circuit Analysis, 7th Edition 44. Chapter Three Solutions 10 March 2006 Since v = 6 V, we know the current through the 1-Ω resistor is 6 A, the current through the 2-Ω resistor is 3 A, and the current through the 5-Ω resistor is 6/5 = 1.2 A, as shown below: By KCL, 6 + 3 + 1.2 + iS = 0 or iS = -10.2 A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
90. 90. Engineering Circuit Analysis, 7th Edition 45. Chapter Three Solutions (a) Applying KCL, 1 – i – 3 + 3 = 0 10 March 2006 so i = 1 A. (b) Looking at the left part of the circuit, we see 1 + 3 = 4 A flowing into the unknown current source, which, by virtue of KCL, must therefore be a 4-A current source. Thus, KCL at the node labeled with the “+” reference of the voltage v gives 4–2+7–i = 0 or i = 9A PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
91. 91. Engineering Circuit Analysis, 7th Edition 46. Chapter Three Solutions 10 March 2006 (a) We may redraw the circuit as Then, we see that v = (1)(1) = 1 V. (b) We may combine all sources to the right of the 1-Ω resistor into a single 7-A current source. On the left, the two 1-A sources in series reduce to a single 1-A source. The new 1-A source and the 3-A source combine to yield a 4-A source in series with the unknown current source which, by KCL, must be a 4-A current source. At this point we have reduced the circuit to Further simplification is possible, resulting in From which we see clearly that v = (9)(1) = 9 V. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
92. 92. Engineering Circuit Analysis, 7th Edition 47. Chapter Three Solutions 10 March 2006 (a) Combine the 12-V and 2-V series connected sources to obtain a new 12 – 2 = 10 V source, with the “+” reference terminal at the top. The result is two 10-V sources in parallel, which is permitted by KVL. Therefore, i = 10/1000 = 10 mA. (b) No current flows through the 6-V source, so we may neglect it for this calculation. The 12-V, 10-V and 3-V sources are connected in series as a result, so we replace them with a 12 + 10 –3 = 19 V source as shown Thus, i = 19/5 = 3.8 A. PROPRIETARY MATERIAL . © 2007 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.
93. 93. Engineering Circuit Analysis, 7th Edition 48. Chapter Three Solutions 10 March 2006 We first combine the 10-V and 5-V sources into a single 15-V source, with the “+” reference on top. The 2-A and 7-A current sources combine into a 7 – 2 = 5 A current source (arrow pointing down); although these two current sources may not appear to be in parallel at first glance, they actually are. Redrawing our circuit, we see that v = 15 V (note that we can completely the ignore the 5-A source here, since we have a voltage source directly across the resistor). Thus, P16Ω = v2/16 = 14.06 W. Returning to the original circuit, we see that the 2 A source is in parallel with both 16 Ω resistors, so that it has a voltage of 15 V across it as well (the same goes for the 7 A source). Thus, P2 A abs = -15(2) = -30 W P7 A abs = -15(-7) = 105 W Each resistor draws 15/16 A, so the 5 V and 10 V sources each see a current of 30/16 + 5 = 6.875 A flowing through them. Thus, P5V abs = -5(6.875) = -34.38 W P 10V abs = -10(6.875) = -68.75 W which sum to -0.01 W, close enough to zero compared to the size of