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Problems
崑山科技大學 100 學年度電機系電路學(一)第一次會考題庫
2.4 A variety of voltage source values were applied to the device shown in Fig. P2.4(a). The power absorbed by the device for
each value of voltage is recorded in the table given in Fig. P2.4(b). Use the values in the table to construct a circuit model for
the device consisting of a single resistor.
Figure P2.4
2.18 The currents i1 and i2 in the circuit in Fig. P2.18 are 20 A and 15 A, respectively.
a) Find the power supplied by each voltage source.
b) Show that the total power supplied equals the total power dissipated in the resistors.
Figure P2.18
2.19 圖 P2.19 電路中的電流 ia 及 ib 其值分別為 4A 及－2A。
a) 求 ig 的值。
b) 求每個電阻器所消耗的功率。
c) 求 υg 的值。
d) 證明：由電流源所供給的功率等於電路中其他元件所吸收的功率。
Figure P2.19
2.21 The voltage and current were measured at the terminals of the device shown in Fig. P2.21(a). The results are tabulated in Fig. P2.21(b).
 2-1 
Circuit Elements
a) Construct a circuit model for this device using an ideal voltage source and a resistor.
b) Use the model to predict the amount of power the device will deliver to a 40Ω resistor.
Figure P2.21
2.22 The table in Fig. P2.22(a) gives the relationship between the terminal current and voltage of the practical constant current
source shown in Fig. P2.22(b),
a) Plot is versus υs.
b) Construct a circuit model of this current source that is valid for 0  vs  75 V, based on the equation of the line plotted in
(a).
c) Use your circuit model to predict the current delivered to a 2.5kΩ resistor.
d) Use your circuit model to predict the open-circuit voltage of the current source.
e) What is the actual open-circuit voltage?
f) Explain why the answers to (d) and (e) are not the same.
Figure P2.22
2.23 The table in Fig. P2.23(a) gives the relationship between the terminal voltage and current of the practical constant voltage
source shown in Fig. P2.23(b).
a) Plot υs versus is.
b) Construct a circuit model of the practical source that is valid for 0  is  24 A, based on the equation of the line plotted
in (a). (Use an ideal voltage source in series with an ideal resistor.)
c) Use your circuit model to predict the current delivered to a 1Ω resistor connected to the terminals of the practical source.
d) Use your circuit model to predict the current delivered to a short circuit connected to the terminals of the practical source.
e) What is the actual short-circuit current?
f) Explain why the answers to (d) and (e) are not the same.
 2-2 
Problems
Figure P2.23
2.24 試調整圖 P2.24 電路中的可變電阻 R，使得 ia 等於 1A，求此時之 R 值。
Figure P2.24
2.25 For the circuit shown in Fig.P2.25, find (a) R and (b) the power supplied by the 500 V source.
Figure P2.25
2.28 Find (a) io, (b) i1, and (c) i2 in the circuit in Fig. P2.28.
Figure P2.28
2.29 a) 求圖 P2.29 電路中的 υy 的電壓值。
b) 證明此電路中所產生的總功率，等於電路所吸收的總功率。
Figure P2.29
 2-3 
Circuit Elements
2.30 For the circuit shown in Fig. P2.30, calculate (a) i△ and υ0 and (b) show that the power developed equals the power absorbed.
Figure P2.30
2.31 Find υ1 and υg in the circuit shown in Fig. P2.31 when υ0 equals 5 V. (Hint: Start at the right end of the circuit and work
back toward υg.)
Figure P2.31
3.11 For the circuit in Fig. P3.11 calculate
a) υ0 and io
b) the power dissipated in the 15 Ω resistor
c) the power developed by the voltage source
Figure P3.11
3.16 Assume the voltage divider in Fig. P3.15 has been constructed from 1 W resistors. How small can RL be before one of the
resistors in the divider is operating at its dissipation limit?
Figure P3.15
3.26 Find υo in the circuit in Fig. P3.26.
 2-4 
Problems
Figure P3.26
3.29 已知圖 P3.29 所示電路中，流過 9 Ω 電阻器之電流為 1 A。
a) 求 υg 值。
b) 求 20 Ω 電阻器所消耗的功率。
Figure P3.29
3.34 A d’Arsonval voltmeter is shown in Fig. P3.34. Find the value of Rυ for each of the following full-scale reading: (a) 50 V,(b)
5 V, (c) 250 mV, and (d) 25 mV.
Figure P3.34
3.43 The voltmeter shown in Fig. P3.43(a) has a full-scale reading of 750 V. The meter movement is rated 75 m V and 1.5 mA.
What is the percentage of error in the meter reading if it is used to measure the voltage υ in the circuit of Fig. P3.43(b)?
Figure P3.43
3.46 Design a d’Arsonval voltmeter that will have the three voltage ranges shown in Fig. P3.46.
 2-5 
Circuit Elements
Figure P3.46
a) Specify the values of R1, R2, and R3.
b) Assume that a 750 kΩ resistor is connected between the 150 V terminal and the common terminal. The voltmeter is then
connected to an unknow voltage using the common terminal and the 300 V terminal. The voltmeter reads 288 V. What is
the unknown voltage?
c) What is the maximum voltage the voltmeter in (b) can measure?
3.55 Find the equivalent resistance Rab in the circuit in Fig. P3.55.
Figure P3.55
3.56 求圖 P3.56 所示電路中的 io 值，以及 30 Ω 電阻器所消耗的功率。
Figure P3.56
3.57 Find Rab in the circuit in Fig. P3.57.
 2-6 