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Unformatted text preview: The charge ﬂowing in a wire is plotted in Fig. 1.24.
Sketch the corresponding current. a (C)
50 2 4 8 t{s) I .8 The current ﬂowing pasta point in a device is shown in
Fig. 1.25. Calculate the total charge through the point. 1' (mA)
10 U l 2 I (ms) 51.9 The current through an element is shown in Fig. 1.26.
' Determine the total charge that passed through the element at:
(a)t=ls (h)t=3s (c)t=55
i (A)
7 10
5
0 1 2 3 4 r(s) Figure 1.26
For Prob. 19. Sections 1.4 and 1.5 Voltage, Power, and Energy 1.10 A lightning bolt with 8 l<A strikes an object for 15 us.
How much charge is deposited on the object? 1. 11 A rechargeable ﬂashlight hatteiy is capable of
delivering 85 mA for about 12 h. How much charge
can it release at that rate? If its terminal voltage is
J .2 V, how much energy can the battery deliver? 1.12 if the current ﬂowing through an element is given by 433A, 0 §t< 6,9
_ 18A, 6 §r<103
ta): —12A, 10 §t< 15s 0, r2153 Plot the charge stored in the element over
0 < r < 20 s. Problems 25 1.13 1.14 1.15 1.16 The charge entering the positive terminal of an
element is g = to sin 47rth
while the voltage across the element (plus to minus) is
v 2 2 cos 4171‘ V (a) Find the power delivered to the element at
t = 0.3 s. (1)) Calculate the energy delivered to the element
between 0 and 0.6 s. The voltage U across a device and the current 1'
through it are ' 0(1) : 5 cos 2: V, jg) = 10(1 7 9705:) A Calculate: (a) the total charge in the device at r = l s (b) the power consumed by the device at r : l s. The current entering the positive terminal of a device is zit) : 3972' A and the voltage across the device is
120‘) = 5di/dtV. (a) Find the charge delivered to the device between
t : 0 and r 2 2 s. (b) Calculate the power absorbed. (c) Determine the energy absorbed in 3 s. Figure 1.27 shows the current through and the voltage
across a device. (a) Sketch the power delivered to the device for r > O. (b) Find the total energy absorbed by the device for
theperiodoft) < t < 43. i (mA)
60 0 2 4 :(s)
y (V)
5
n 2 4 t (s) _5 i_ Figure 1.21
For Prob. 1.16. Section 1.6 Circuit Elements 1.17 Figure 1.28 shows a circuit with ﬁve elements. If p1 = *205W,p2 = 60W,p4 = 45W,p5 z 30W,
calculate the power [23 received or delivered by
element 3. ' ‘f 26 Chapter’l Basic Concepts Section 1.7 Applications 1.21 A 60mW incandescent bulb operates at 120 V. How
many electrons and coulombs ﬂow through the bulb
in one day? 1.22 A lightning bolt strikes an airplane with 30 icA for
2 ms. How many coulombs of charge are deposited
on the plane? 1.23 A 1.87kW electric heater takes 15 min to boil a
quantity of water. If this is done once a day and Figure 1.28
For Prob. 1.17. 1.18 Find the power absorbed by each of the elements in Flg' 1'29" power costs 10 cents/kWh. what is the cost of its
operation for 30 days?
p I = 10 A +10 V_ +8 V_ 4 A 1.24 A utility company charges 8.5 cents/kWh. If a
—b— 4—
_ l . i— E:l— consumer operates a 40W light bulb continuously
: P: l 14 A .04 for one day, how much is the consumer charged?
_ + + Pi 1.25 A 1.2kW toaster takes roughly 4 minutes to heat 30 V 1,] 20 V Ps 12 V ‘ four slices of bread. Find the cost of operating the
I e 7 0'41 toaster once per day for 1 month (30 days). Assume
: ‘ energy costs 9 cents] kWh.
i 1.26 A ﬂashlight battery has a rating of 0.8 ampere—hours
Figure 1.29 (Ab) and a lifetime of 10 hours.
3 For Pmb' 1‘18' (a) How much current can it deliver?
i (b) How much power can it give if its terminal
1.19 Find 1 in the network of Fig. 1.30. voltage is 6 V?
i i (c) How much energy is stored in the battery ¢ 1 A i I 1n kWh?
1.27 A constant current of 3 A for 4 hours is required
2 V to charge an automotive battery. If the terminal
+ + voltage is 10 + t/2 V, where ris in hours,
4 A o 9 v 9 v ‘ .
' — 7 (a) how much charge rs transported as a result of the
” 6 V charging?
(b) how much energy is expended?
(c) how much does the charging cost? Assume
Figure 1.30 electricity costs 9 cents/kWh.
For Pmb 119 1.28 A 30W incandescent lamp is connected to a 120V
source and is left burning continuously in an
i 130 Find V” in the Circuit of Fig. 1.31. ' otherwise dark staircase. Determine:
(a) the current through the lamp.
10: 2 A (h) the cost of operating the light for one nonleap year if electricity costs 12 cents per kWh. 1.29 An electric stove with four burners and an oven is
used in preparing a meal as follows.
Burner 1: 20 minutes Burner 2: 40 minutes
Burner 3: 15 minutes Burner 4: 45 minutes Oven: 30 minutes If each burner is rated at 1.2 kW and the oven at
1.8 kW, and electricity costs 12 cents per kWh,
Figure 1.31 calculate the cost of electricity used in preparing
For Prob. 1.20. the meal. Problems 61
2.9 Which of the circuits in Fig. 2.66 will give you 2.10 In the Circuit of Fig. 2.67, a decrease in R3 leads to a
Vat, = 7 V? decrease of:
(a) current through R3 (b) voltage across R3
((3) voltage across R I
(d) power dissipated in R2 (e) none of the above R1 V5 0 R2 R3 Figure 2.61
For Review Question 2.10. Answers: 2.1c, 2.2C, 2.35, 2.4a, 2.50, 2.6b, 2. 70, 2.8d, 3
2.9d, 2.1019, (1'. (C) (d)
Figure 2.66
For Review Question 2.9. 1 Section 2.2 Ohm’s Law '
I 2.1 The voltage across a 5H) resistor is 16 V. Find the
current through the resistor.
2.2 Find the hot resistance of a iighthulb rated 60 W, 120 V.
2.3 A bar of silicon is 4 cm long with a circular cross sec
tion. If the resistance of the bar is 240 .Q at room tem—
perature, what is the crosssectional radius of the bar? 2.4 (a) Calculate current i in Fig. 2.68 when the switch is Figure 2.69
in position 1. For Prob. 2.5. (b) Find the current when the switch is in position 2. 2.6 In the network graph shown in Fig. 2.70, determine
1 2 the number of branches and nodes. Figure 2.68
For Prob. 2.4. " Section 2.3 Nodes, Branches, and Loops 2.5 For the network graph in Fig. 2.69, ﬁnd the number Figure 2.10
of nodes, branches, and ioops. For Prob. 2.6. 68 Chapter 2 Basic Laws 2.7 Dcterrnjne the number of branches and nodes in the 2.11 In the circuit of Fig. 2.75, calculate V1 and V2.
circuit of Fig. 2.71. IQ 4Q
lzvuzA Figure 2.11 Figure 2.15
For Prob. 2.7. For Prob. 2.11. seCtlon 2'4 Kerthﬁs Laws 2.12 It: the circuit ofFig. 2.76, obtain 01, v2, and v3. 2.8 Use KCL to obtain currents i1, i2, and [3 in the circuit shown in Fig. 2.72. 15 V
+ m
12 mA
8 mA +
9 mA
Figure 2.12 Figure 2.16
For Prob. 2.8. For Prob. 2.12.
2.9 Find fl, 1'2, and 1'3 in Fig. 2.73. 2.13 For the circuit in Fig. 2.77, use KCL to ﬁnd the branch currents I l to 14. F" Figure 2.13
For Prob. 2.9. Figure 2.11
For Prob. 2.13. 2.10 Determine i1 and i2 in the circuit of Fig. 2.74.
2.14 Given the circuit in Fig. 2.78, use KVL to ﬁnd the branch voltages V] to V4. Figure 2.14 Figure 2.18
For Prob. 2.10. For Prob. 2.14. ...
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This note was uploaded on 02/01/2011 for the course BME 311 taught by Professor Zhang during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Zhang

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