东南大学电子学院《电路基础》期末考试样卷及答案

Solve the following problems. (100 points)1、( 6 points) Find U ab in the circuit in Figure 1.Figure 1a b2、( 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.aFigure 34、( 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 4u5、( 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 yparameters for the circuit in Figure 6.∙∙Figure 67、( 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 ,Ω20/1=C ω,V )302cos(50cos 10080)(︒+++=t t t u s ωω.Figure 72u s8、( 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 8V ︒∠050ω=103∙rms9、( 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 9u 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: Pleasemark the key data in your graph.)Figure 1010ΩSolve the following problems. (100 points)1、( 6 points) Find U ab in the circuit in Figure 1.Figure 1a bSolution:U ab = 9V2、( 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.aFigure 3Solution: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 4uSolution:pF 5.12)1(≈C .126)2(≈Q μA 150)3(=rms I mV 190)4(=Crms U5、( 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 U6、( 8 points) Find the y parameters for the circuit in Figure 6.∙∙Figure 6Solution:[]S y ⎥⎦⎤⎢⎣⎡=0.540.02 2.0 7、( 15 points) For the circuit in figure 7, find the rms value of the current i andthe average power absorbed by the circuit, given that Ω10=L ω,Ω51=R ,Ω202=R ,Ω20/1=C ω,V)302cos(50cos 10080)(︒+++=t t t u s ωω.Figure 72u sSolution:A 17.6357.2714.42.3222222120=++=++=I I I I rmsP =P 0+P 1+P 2=256+333.28+50=639.28W8、( 12 points) In the circuit of Figure 8, determinate the value of Z that willabsorb the maximum power and calculate the value of the maximum power.Figure 8V ︒∠050ω=103∙rmsSolution:If Ω135jZ Z eq+==*, Z will absorb the maximum average power. The maximum average power is, W 7.2491356.1941412max=⋅=⋅=*eq OC R U P9、( 14 points) If the switch in Figure 9 has been closed for a long time and isopened at t = 0, find u c , i L , u k for t ≥ 0.20Figure 9u c +-Solution:0 A,5.15.1)5.10(5.14040>-=-+=--t e e i t t L ，0 V,60120)12060(12020/20/>-=-+=--t e e u t t C 0 ,V 6030902020/40>+--=-=--t e e u i u t t C L K10、( 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: Pleasemark the key data in your graph.)Figure 1010ΩSolution: A25.125.132t t e e i ---=。