东南大学电子学院《电路基础》期末考试样卷及问题详解
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Solve the following problems. (100 points)
1、( 6 points) Find U ab in the circuit in Figure 1.
Figure 1
a b
2、( 8 points) Find u o and i o in the circuit in Figure 2.
u o Figure 2
-
3、( 6 points) In the circuit of Figure 3, readings of voltmeter ○V1，○V2 and ○
V3 are 10V , 18V and 6V , respectively. Please determinate the reading of the voltmeter ○V
.
a
Figure 3
4、( 8 points) The resonant or tuner circuit of a radio is portrayed in Figure 4, where u s1 represents a broadcast signal, given that R =10Ω，L =200μH , U s1rms =1.5mV ，f 1=1008kHz. If the circuit is resonant with signal u s1, please determinate: (1) the value of C ; (2) the quality factor Q of the circuit; (3) the current I rms ; (4) the voltage U c rms .
Figure 4
u
5、( 8 points) A balanced three-phase circuit is shown in Figure 5. Calculate the phase currents and voltages in the delta-connected load Z, if V U A ︒∠=•
0220, Z =(24+j15)Ω，Z L =(1+j1)Ω.
Figure 5
•
6、( 8 points) Find the y
parameters for the circuit in Figure 6.
•
•
Figure 6
7、( 15 points) For the circuit in figure 7, find the rms value of the current i and the average power absorbed by the circuit, given that Ω10=L ω,
Ω51=R ,Ω202=R ,Ω
20/1=C ω,V )302cos(50cos 10080)(︒+++=t t t u s ωω.
Figure 7
2
u s
8、( 12 points) In the circuit of Figure 8, determinate the value of Z that will absorb the maximum power and calculate the value of the maximum power.
Figure 8
V ︒∠050ω=103•
rms
9、( 14 points) If the switch in Figure 9 has been closed for a long time and is opened at t = 0, find u c , i L , u k for t ≥ 0.
20Figure 9
u c +-
10、( 15 points) The switch in Figure 10 has been in position a for a long time. At t = 0, it moves to position b. Find i 2(t) for t ≥ 0 and sketch it. (Attention: Please
mark the key data in your graph.)
Figure 10
10Ω
Solve the following problems. (100 points)
1、( 6 points) Find U ab in the circuit in Figure 1.
Figure 1
a b
Solution:
U ab = 9V
2、( 8 points) Find u o and i o in the circuit in Figure 2.
u o Figure 2
-
Solution:
V 4.2=o u , 0.256mA -=o i
3、( 6 points) In the circuit of Figure 3, readings of voltmeter ○V1，○V2 and ○
V3 are 10V , 18V and 6V , respectively. Please determinate the reading of the voltmeter ○V
.
a
Figure 3
Solution:
The reading of the voltmeter ○V is 10V .
4、( 8 points) The resonant or tuner circuit of a radio is portrayed in Figure 4, where u s1 represents a broadcast signal, given that R =10Ω，L =200μH , U s1rms =1.5mV ，f 1=1008kHz. If the circuit is resonant with signal u s1, please determinate: (1) the value of C ; (2) the quality factor Q of the circuit; (3) the current I rms ; (4) the voltage U c rms .
Figure 4
u
Solution:
pF 5.12)1(≈C 6.126)2(≈Q μA 150)3(=rms I mV 190)4(=Crms U
5、( 8 points) A balanced three-phase circuit is shown in Figure 5. Calculate the phase currents and voltages in the delta-connected load Z, if V U A ︒∠=•
0220, Z =(24+j15)Ω，Z L =(1+j1)Ω.
Figure 5
•
Solution:
A 3.69-11.74''︒∠=•
B A I , V 31.28332''︒∠=•
B A U
6、( 8 points) Find the y parameters for the circuit in Figure 6.