南京信息职业技术学院第四章(正弦交流电路)练习题详解
第四章
【第四章练习题】:
4-1(如图所示,当选择电流参考方向由a向时,电流的解析式为b
2。如选择参考方向相反,解析式如何写法,求i,28.2sin(314t,,)A3
两种情况下时,电流的瞬时值。 t,0.01s
i,a4-1(; i,,i,28.2sin(314t,)Abbaab3R
:;; i,24.42Ai,,24.42At,0.01s练习题4-1图 abba
2解: i,i,28.2sin(314t,,)Aab3
参考方向相反,则:
,,22 i,,i,,28.2sin(314t,)A,28.2sin(314t,,,)Abaab33
, ,28.2sin(314t,)A3
2,: i/,28.2sin(314,0.01,)A,28.2sin,24.42At,0.01s,abt,0.0133
4,, i/,28.2sin(314,0.01,)A,28.2sin,,24.42Abat,0.0133
,4-2(已知一正弦电流,试写出其振幅值、角频率、频i,10sin(314t,)A6
率和周期以及初相位。
,4-2(;;;; ,10A314rad/s50Hz0.02s6
,解: i,10sin(314t,)A6
初相位 振幅 角频率
,1314T,,0.02s,,2,f,314 f,,,50Hzf,22,3.14
134
第四章
,4-3(按照已选定的参考方向,电流,如果把参考方向i,54sin(314t,)A3
选定成相反的方向,则电流的解析式应如何写法。
2,4-3(; i,54sin(314t,)A3
,,,解: i,,i,,54sin(314t,)A,54sin(314t,,,)A33
2, ,54sin(314t,)A3
4-4(已知工频电流在T4时为,写出这电流的解析式(假定初相为零)。 5A
4-4(; i,5sin(,t)A
2T,解:i,Isin(,t,,)A 代入: 5,Isin(,,0)AmmT4
? I,5A m
? i,5sin(314t)A
4-5(一个工频正弦电压的最大值为,初始值为,试求它的解537V,268.5V
析式。
4-5(u,537sin(314t,30:)V;
u,Usin(,t,,)VU,537V解: mm
268.5 ,268.5,537sin(,,0,,) sin,,,,,0.5537
? ,,,30: 工频:f,50Hz
u,537sin(314t,30:)V?
135
第四章 4-6(已知, ,试指出各正弦u,311sin(3140t)Vu,311sin(3140t,,3)VAB
量的振幅值、有效值、初相、角频率、周期以及两个正弦量与之uuAB
间相位差为多少。
解: u,311sin(3140t)VU,311VU,220VAAm
rad ,3140,,0,s
f,500HzT,0.002s
u,311sin(3140t,,3)V U,311V U,220VBAm
,rad ,3140 ,,,,s3
,, 0()f,500Hz,,,,,,,T,0.002s,,,AB33
uu4-7(图4-1给出和的波形,问和的初相各为多少,相位差为多少, iii
u和哪个越前,越前多少,
ui u
i
,54,, 2,3330,t,,,2 ,33
习题4-7的图 2,,,4-7(;;; i(t),Isin(t,)Au(t),Usin(t,)V,,rad/s,,, mmui333
,,解:如图 ,,,,,iu33
2,,, ,,,,,,,,rad/s,,,ui333
电流超前,电压滞后。
136
第四章
3,4-8(已知,,,,写出它们的解析式,I,1AE,10V,,,,,,mmEi42
并说明哪个越前,哪个滞后(角频率均为。 ,,31400rad/s)
,,4-8(;; u(t),10sin(31400t,)Vi(t),sin(31400t,)A42
,解: u(t),10sin(31400t,)V4
,,33 i(t),sin(31400t,)A,sin(31400t,,2,)A22
, ,sin(31400t,)A2
,,, ,,,,,,,,,,ui424
电流越前,电压滞后。
4-9(三个正弦电流i,i,i的最大值分别为,,。若i较i越前1A2A3A12312
,较i滞后,试以i为参考量,写出三个电流的解析式。 30:150:33
4-9(i(t),sin(,t,150:)Ai(t),2sin(,t,180:)Ai(t),3sin(,t)A;;; 123解:以i为参考量,则:,,0 33
,,,,,150:,,,150: ? 131
,,,,30:,,,180: 122
i(t),sin(,t,150:)A? ; 1
i(t),2sin(,t,180:)A; 2
i(t),3sin(,t)A; 3
137
第四章
4-10(三个正弦电动势
e,141sin(314t)V;A
2, e,141sin(314t,)V;B3
2, e,141sin(314t,)V;C3
试问:(1)比越前多少,比越前多少,比越前多少, eeeeeeABBCCA
(2)若选为参考正弦量,试重写它们的解析式。 eB
222,,,4-10((1);;; ,rad/s,rad/s,rad/s,,,ABBCCA333
2, (2);e,141sin314tV; e,141sin(314t,)VBA3
2,; e,141sin(314t,)VC3
22,,解:(1) ,,,0,(,),rad/s,,,ABAB33
22442,,,,, ,,,,,,,,,,2,rad/s,,,,BCBC33333
22,, ,,,,0,rad/s,,,CACA33
(2)若选为参考正弦量,则: eB
22,,,,0 ,,,,,BAC33
2,e,141sin314tV? ;; e,141sin(314t,)VBA3
2, e,141sin(314t,)VC3
138
第四章
4-11(已知,,求电压和电流的平均值i,120sin(,t,30:)Au,500sin,tV
及有效值。
4-11(;;;; U,318.47VI,76.43AU,353.5VI,84.85Aavav解: 则: U,500Vu,500sin,tVm
U2m U,,353.5VU,U,318.47Vavm,2
则: I,120A i,120sin(,t,30:)Am
I2m I,,84.85AI,I,76.43Aavm,2
2,-12(设电流,在时,,求电流有效值。 4i,Isin(t,)At,0i,0.433A,m3
4-12(; I,0.3535A
22,,解: i,Isin(t,)A0.433,Isin(,0,)A,,mm33
0.433 ? I,,0.5Am0.866
I0.5m ? I,,,0.354A 22
4-13(用交流电压表测得市电的线电压为,问线电压的最大值为多少, 380V4-13( 537.4V
U,2,U,2,380,537.4V解: m
139
第四章
4-14(将下列复数写成代数式:
(1); (2) ; (3) ; 8,90:6,,90:20,60:
(4) ; (5) ; (6) ; 30,,70:220,,120:12,95:4-14((1);(2);(3); 10,j17.32j8,j6
(4);(5); 10.26,j28.19,110,j190.5
(6) ; ,1.05,j11.95
解:(1) ; (2) ; 8,90:,j86,,90:,,j6
(3) ; 20,60:,20cos60:,j20sin60:,10,j17.32
(4) ; 30,,70:,30cos,70:,j30sin,70:,10.26,j28.19
(5) ; 220,,120:,220cos,120:,j220sin,120:,,110,j190.53
(6) ; 12,95:,12cos95:,j12sin95:,,1.049,j11.95-15(将下列复数写出极坐标式: 4
(1) ; (2) ; (3) ; 4,j6,3,j4,7,j4
(4) ;(5) 20,j30; (6) ; 0.26,j0.0816,j124-15((1);(2) ; 7.21,56.3:5,126.87:
(3) ;(4) ; 8.06,,150.26:0.272,17.1:
(5) ;(6) ; 36.06,,56.3:20,36.9:
622解:(1); 4,j6,4,6,arctan,7.21,56.3:4
,322(2) ; ,3,j4,3,4,arctan,5,126.87:4
,722(3) ; ,7,j4,7,4,arctan,8.06,,150.26:,4
0.2622(4) ; 0.26,j0.08,0.26,0.08,arctan,0.272,17.1:0.08
2022(5) 20,j30,20,30,arctan,36.06,,56.3:,30
1622(6) ; 16,j12,16,12,arctan,20,36.9:12
140
第四章
,,,,,,,,,,4-16(已知,,求;;;。 A,8,j6A,6,j8A,AA,AA,AA,A1212121212-16(;;;; 419.8,45:2.83,,45:100,90:1,,16.2:
,,解: A,A,8,j6,6,j8,14,j14,19.8,45:12
,,A,A,8,j6,(6,j8),2,j2,2.83,,45: 12
,,A,A,(8,j6),(6,j8),(10,36.8:),(10,53.1:),100,90: 12
,,A,A,(8,j6),(6,j8),(10,36.8:),(10,53.1:),1,,16.2: 12
,,,,,,,,,,B,8,,60:B,10,150:B,BB,BB,BB,B4-17(已知,,求;;;。 12121212124-17(;;;; 5.07,,156.77:17.44,,46.53:80,90:0.8,,150:
,,B,8,,60:,4,j6.93B,10,150:,,8.66,j5解: 12
,,B,B,4,j6.93,8.66,j5,,4.66,j1.93,5.04,,157.5: 12
,,B,B,4,j6.93,8.66,j5,12.66,j11.93,17.395,,46.7: 12
,,B,B,8,,60:,10,150:,80,90: 12
,,B,B,8,,60:,10,150:,0.8,,210: 12
,0.8,(,210:,360:),0.8,,150:
141
第四章
ZZ124-18(求下列各题中及; Z,Z12Z,Z12
(1) ,; Z,j8,Z,6,12
(2) ,; Z,8,,60:,Z,4,30:,12
(3) ,。 Z,3,0:,Z,3,,90:,12
4-18((1) ;;(2) ;; 10,53.1:,4.8,36.9:,8.98,,33.83:,3.56,3.83:,
(3) ;; 4.24,,45:,2.12,,45:,解: (1) ,Z,6,; Z,j8,12
Z,Z,j8,6,10,53.1:, 12
ZZj8,648,90:12 ,,,4.8,36.9:,ZZj,8,610,53.1:12
(2) Z,8,,60:,,4,j6.93,Z,4,30:,3.46,j2; 12
Z,Z,8,,60:,4,30:,4,j6.93,3.46,j2 12
,7.46,j4.93,8.98,,33.83:,
ZZ8,,60:,4,30:12,,3.56,3.83:, ZZ,8.98,,33.83:12
Z,3,0:,3Z,3,,90:,,j3, (3) ,。 12
Z,Z,3,j3,4.24,,45:, 12
ZZ3,0:,3,,90:12,,2.12,,45:, ZZ,4.24,,45:12
142
第四章
4-19(下列电压和电流中:
;; u,Usin(,t,,)u,Usin(,t,,)1m112m22
;; u,Usin(3,t,,)i,Isin(,t,,)3m334m44
;; i,Isin(3,t,,)i,Isin(3,t,,)5m556m66
哪几个正弦量能用向量法进行加减运算。 4-19(频率相同才能进行相加减。
解: u,Usin(,t,,)和u,Usin(,t,,)可以进行加减运算; 1m112m22
i,Isin(3,t,,)和i,Isin(3,t,,)可以进行加减运算; 5m556m66
4-20(写出下列各正弦量的对应向量:
u,1002sin(,t,25:)V (1) ;
i,102sin(,t,90:)A (2) ; 1
i,7.07sin(,t)A; (3) 2
4-20((1) ;(2) ;(3) ; 100,25:V10,90:A5,0:A
,u,1002sin(,t,25:)V解: (1) ; U,100,25:V
,i,102sin(,t,90:)AI,10,90:A (2) ; 11
,I,5,0:Ai,7.07sin(,t)A (3) ; 22
143
第四章
4-21(写出下列各相量的对应正弦量(): f,1000Hz
,, (1); (2); I,3,j6AI,j12A21
,,(3); (4); U,200,,60:VU,220,120:V12
i,6.72sin(2000,t,63:)Ai,122sin(2000,t,90:)A4-21((1) ;(2) ; 12
u,2002sin(2000,t,60:)V (3) ; 1
u,2202sin(2000,t,120:)V(4) ; 2
,i,6.72sin(2000,t,63:)AI,3,j6,6.7,,63:A解: (1) 11
,i,122sin(2000,t,90:)AI,j12,12,90:A(2) 22
,u,2002sin(2000,t,60:)VU,200,,60:V (3) 11
,u,2202sin(2000,t,120:)VU,220,120:V(4) 22
144
第四章
4-22(求下列各组正弦量之和
u,2202sin(,t)Vu,2202sin(,t,120:)V(1) ; 12
i,102sin(3140t,60:)Ai,82sin(3140t,30:)A (2) ; 12
u,2202sin(,t,60:)Vi,12.812sin(3140t,21.34:)A4-22((1) ;(2)
,u,2202sin(,t)V解:(1) U,220,0:V 11
,u,2202sin(,t,120:)V U,220,120:V 22,,U,U,220,0:,220,120:,220,110,j190.53 12
,110,j190.53,220,60:V
u,2202sin(,t,60:)V?
,i,102sin(3140t,60:)AI,10,60:A(2) ; 11
,i,82sin(3140t,30:)AI,8,,30:A 22,,I,I,10,60:,8,,30:,5,j8.66,6.93,j4 12
,11.93,j4.66,12.81,21.34:A
i,12.812sin(3140t,21.34:)A?
145
第四章
4-23(将下列各正弦量绘成相量图
(1) ; i,2sin(3140t,30:)A1
(2) ; u,100sin(3140t)V
(3) ; i,3sin(3140t,45:)A2
,解: (1) ; I,2,,30:A i,2sin(3140t,30:)Am11
,I m1
30: ,1
,u,100sin(3140t)V (2) ; U,100,0:V m
,Um ,1
,I,3,45:A (3) i,3sin(3140t,45:)A; m22
,Im2
45: ,1
4-24(在电阻的两端外施电压u,12.5sin(314t,60:)V;写出电阻中电25,
流的解析式,并做出电流和电压的相量图。
i,0.5sin(314t,60:)A4-24(;
,1
60:,U,12.5,,60:VZ,25,0:,解: mR
12.5,,60:,,I I,,0.5,,60:Amm25,0:
i,0.5sin(314t,60:)A? ,Um
146
第四章
4-25(有一、的电炉,接在的交流电源上,试求通过电炉220V10kW220V
的电流和正常工作时的电阻。
-25(;; 4I,45.45AR,4.84,
22220U解: ,R,,4.84,P3R10,10
3P10,10 I,,,45.45AU220
4-26(已知在的电阻上通过的电流,试求电阻两端i,5sin(314t,30:)A10,
电压的有效值,写出电压解析式并算出该电阻消耗的功率。
4-26(;; u,50sin(314t,30:)VP,125W
,解: Z,10,0:,I,3.54,30:AR
, U,3.54,30:,10,0:,35.4,30:V
u,35.42sin(314t,30:)V? u,50sin(314t,30:)V
P,U,I,35.4,3.54,125W
4-27(额定值为、的灯泡,接在、的交流电源上,220V100W220V50Hz
允许电压波动,试求在电压最高时及最低时灯泡的实际功率(灯15%
泡的电阻假定不变)。
4-27(;; 72.25W132.25W
22U220R解: ,,,484,P100
, 最高电压:U,(1,0.15),220,253V
22U253, P,,,132.25WR484
,,U,(1,0.15),220,187V最低电压:
22U187,, P,,,72.25WR484
147
第四章 4-28(已知一线圈通过的电流时,其感抗为,试问电源频率为50Hz10,
,其感抗为多少, 10kHz
4-28(; 2k,
10解: X,,L,2,3.14,50,LL,,0.0318HL314
103, X,,L,2,3.14,10,10,,2000,L314
4-29(已知,电路的电流为,电压为,求电源的频率。 L,0.5mH3.18mA10V
64-29(f,10Hz;
U10解: X,,,3.145k,L,3I3.18,10
3X3.145,106L f,,,10Hz,3,2L2,3.14,0.5,10
u4-30(具有电感的电路上,外施电压,选定、参u,170sin(300t)V80mHi
考方向一致时,写出电流的解析式,并做出电流和电压的相量图。 4-30(; i,7sin(300t,90:)A
,,3Um解: Z,j,L,j300,80,10,j24, L,1
90:,U170m,I,,,7.08,,90:A mZj24L
,Imi,7.08sin(300t,90:)A
148
第四章
4-31(已知一线圈的电感为(电阻忽略不计),先后接在及 f,50Hz0.15H
、电压为的电源上,试分别计算在上述两种情况下f,10000Hz220V
的感抗,通过线圈的电流及无功功率。 4-31((1);;; X,47.1,Q,1027.4varI,4.67AL
(2);;; X,9420,Q,5.138varI,0.023AL
解: (1) X,,L,2,3.14,50,0.15,47.1,L
U220 I,,,4.67AX47.1L
Q,U,I,220,4.67,1027.6var
(2) X,,L,2,3.14,10000,0.15,9420, L
U220 I,,,0.0234AX9420L
Q,U,I,220,0.0234,5.138var
4-32(选定u、i参考方向一致,已知加于电感元件两端的电压为
时,通过的电流为i,100sin(125600t,,)mA,试u,120sin(125600t)V
求L值和电流的初相。 ,
4-32(;L,9.55,H; ,,90:
,,I,100,,,AU,120,0:V解: mm
,U120,0:mZ,,,1.2,,, ,,90: L,I100,,,m
X1.2,6LX,1.2,L,,,9.55,10H,9.55,H L2f125600,
149
第四章
4-33(把一个的电容器先后接在及、电压为100,Ff,50Hzf,5000Hz
的电源上,试分别计算在上述两种情况下的容抗,通过电容的电220V
流及无功功率。
4-33((1);;; X,31.85,Q,1519.76varI,6.908AC
(2);;; X,0.3185,Q,151976varI,690.8AC
11解: (1) X,,,31.85,C,6,C314,100,10
U220 I,,,6.908AX31.85C
Q,U,I,220,6.908,1519.76var
11 (2) X ,,,0.3185,C,6,C31400,100,10
U220 I,,,690.74AX0.3185C
Q,U,I,220,690.74,151976var
4-34(电容为的电容器,接在电压的电源上,写出20,Fu,600sin(314t)V
电流的解析式并计算出无功功率。
4-34(i,3.768sin(314t,90:)A;Q,1130.4var;
11Zj解: ,,,,,90:,159.24,,90:,C,6,C314,20,10
,U600,0:m,I,,,3.768,90:A mZ159.24,,90:C
i,3.768sin(314t,90:)A ?
UI600,3.768mm,,,,,,1130.4var QUI222
150
第四章
4-35(两个同频率正弦电压、的有效值各为、。问:(1)什uu40V30V12
么情况下的有效值为;(2)什么情况下的有效值为u,uu,u70V1212
;(3)什么情况下的有效值为; u,u10V50V12
4-35((1)同相;(2)反相;(3)正交;
4-36(如图 (a)、()所示电路,已知电流表(A)(A)(A)的读数均为,b10A123
)的读数。 求电路中电流表(A
A, A,
RLC LC
uuAAA 13A2A12
,,
习题4-36图
a4-36(() ;() ; 0Ab10A
VVV4-37(如图所示电路中,电压表()()()的读数均为,求电路中电50V123
压表()的读数。 VCRL
VVV3124-37(; 50V
V
u,, 习题4-37图
151
第四章
4-38(如图所示电路中,电压表()的读数为,() 的读数为,() VV32V20VV13
的读数为,分别求出() 、()的读数。 VV40V24
,
VV31CC21 Vu
LVV4 R2
,
习题4-38图 4-38(V,24V;V,60V; 24
4-39(日光灯的等效电路如图所示,已知灯管电阻R,280,,镇流器的电1
阻,电感,电源为民用电电压,求电路总R,20,L,1.65HU,220V
R1电流及各部分电压U、U。 I12,
uR1 u镇流器2220V,
L
, 习题4-39图
U,102.89VU,190.29V4-39(;;; I,0.367A12
Z,R,0:,,280,0:,解: 11
X,,L,314,1.65,518.1, L
Z,R,jX,20,j518.1,518.49,87.79:, 2L
Z,Z,Z,280,20,j518.1,598.69,59.93:, 12
,U220,0:, I,,,0.367,,59.93:AZ598.69,59.93:
,,U,I,Z,0.367,,59.93:,280,0:,102.76,,59.93:V 11
,,U,I,Z,0.367,,59.93:,518.49,87.79:,190.29,27.86:V 22
152
第四章 4-40(用电感降压来调速的电风扇的等效电路如图4-6所示,已知,R,190,
,电源电压、,要使,问串X,260,U,180Vf,50HzU,220VL12
LX,联的电感应为多大。 LX
Ri4-40(; L,0.27HXu2u1
L2222解: Z,R,X,190,260,322.02,2L1,U180习题4-40图 2 ? I,,,0.56AZ322.022
U220 Z,,,392.86,I0.56
22 求得:X,83.86, Z,190,(X,260),392.86,LXLX
X83.86LX? L,,,0.27HX,314
u,2202sin(314t,30:)V4-41(已知一电阻和电感串联电路,接到的电源
i,52sin(314t,15:)A上,电流,试求R、L和P。 4-41(;;; R,31.11,L,0.01HP,777.75W
,,解: U,220,30:VI,5,,15:A
,U220,30: Z,,,44,45:,31.11,j31.11,5,,15:I
X31.11L? L,,,0.099HR,31.11,,314
2 P,UIcos45:,220,5,,777.82W 2
153
第四章
u,2202sin(314t,30:)V4-42(电阻,电感的串联电路接 R,30,L,4.78mH
的电源上,试求i、P 、Q及S。
i,7.32sin(314t,27.1:)A4-42(;; P,1609.94W
;; Q,80.5varS,1611.64VA
,3解: X,,L,314,4.78,10,1.5,L
Z,R,jX,30,j1.5,30.04,2.86:, L
, U,220,30:V
,U220,30:, I,,,7.32,27.14:AZ30.04,2.86:
i,7.322sin(314t,27.14:)A?
S,UI,220,7.32,1610.4VA
P,Scos,,1610.4,cos2.86:,1608.39W Z
Q,Ssin,,1610.4,sin2.86:,80.35var Z
4-43(交流接触器的线圈,,试问: R,220,L,63H(1)当接到交流电源时,电流为多少, 220V
(2)若错接到直流电源上时,此时电流又为多少, 220V
4-43((1) ;(2) ; 1A0.011A
Z,R,jX,220,j63,314,220,j19782,19783.22,89.36:,解: (1) L
U220I,,,0.011A Z19783.22
Z,R,jX,220,0,220,0:,(2) L
U220I,,,1A Z220
154
第四章
4-44(已知一线圈在、电路中的电流为,在、时电1A50Hz50V100Hz50V
流为,求线圈的电阻和电感各为多少, 0.8A
4-44(;; R,45.1,L,68.9mH
5022解: ,R,(314L)1
5022 ,R,(628L)0.8
解之得: R,45.069,L,68.95mH
,4-45(一电压与含有固定的和可变的X相串联的电路联U,25,180:VRL
,接。感抗取某一值时得到电流,调节X使电流滞后电I,11.2,153:AL
压,此时电流有效值为多少, 60:
4-45(; I,6.29A
,,解: U,25,180:VI,11.2,153:A
,U25,180: Z,,,2.232,27:,,1.9887,j1.01,11.2,153:I
,,, ? I,I,120:AR,1.9887,
,U252525,? Z,,,60:,,cos60:,jsin60:,,,,,IIII
2525, ? cos60:,1.9887I,,cos60:,6.29A,I1.98874-46(电阻,电容C,25,F的串联电路,接到u,1002sin500tV的R,40Ω
,电源上,试求并画相量图。 I
,4-46( I,1.12,63.4:A
,I1解: Z,,jX,,j,,j80,CC,6500,25,10
Z,R,jX,40,j80,89.44,,63.43:, C,U63.43:,1,U100,0:,I,,,1.12,63.43:A Z89.44,,63.43:
155
第四章 4-47(串联电路中已知电源电压,,u,2202sin31400tVRCR,318,
,,,,求、U、U并画相量图。 C,10,FIRC
,,,4-47(;U,220,0.57:V;U,2.19,,89:V I,0.69,0.57:ARC
1解: Z,,jX,,j,,j3.18,CC,631400,10,10
, Z,R,jX,318,j3.18,318.02,,0.57:,,UCIR
,1,U220,0:,,U I,,,0.69,0.57:A,Z318.02,,0.57:UC
,,U,I,Z,0.69,0.57:,318,220,0.57:V RR
,,U,I,Z,0.69,0.57:,3.18,,90:,2.19,,89.43:V CC
U,5V4-48(如图所示,如果,输入电压,,要使输C,0.1,Ff,50Hzi
,,UU出电压较输入电压滞后60º,问电阻应为多大,输出电压大小为0i
多少, R,,,,U解: RIi,1
C60:u u0i
, ,U,,,UiU0C,,
习题4-48图 R30:11X,,,31847.134,XC,6CZ,C314,0.1,10
XC ,tan30:R
XC R,,55160.85,,55.2k,tan30:
输出电压大小为 2.5V
156
第四章
4-49(若上题中,电压频率为,,要使输出U,2VC,0.01,Ff,600Hzi
,,,电压U 较输入电压U滞后,问电阻应为多大,此时U等于多30:0iR
少,
,4-49(;U,1,60:V R,15.3k,R
,URR,1解: ,I60:
30:
XCZ
,U,iUC,,,U 0
,,U,2,0:VU,1,60:V ? iR
11 X,,,26539.28,C,6,C2,3.14,600,0.01,10
XXCC ,tan60:R,,15322.46,,15.3k,Rtan60:
157
第四章
u,2sin(2,,1180t)V4-50(如图所示电路中,已知,,R,5.1k,i
,试求: C,0.01,F
(1) 输出电压; U0
(2) 输出电压比输入电压越前的相位差;
(3) 如果电源频率增高,输出电压比输入电压越前的相位差增大还是减
C,,小。
uRu0i
,, 习题4-50图 4-50((1)U,354mV; (2); (3) 减小 69.3:O
,U,1,0:V解: R,5.1k,i
11 X,,,13.49k,C,6,C2,3.14,1180,0.01,10
Z,R,jX,5.1,j13.49,14.42,,69.29:k, C
,U1,0:i, I,,,0.069,69.29:mAZ14.42,,69.29:
,,U,I,Z,0.069,69.29:,5.1,0.354,69.29:V 0R
输出比输入超前 69.29:
,X 如果: 则 f,C
158
第四章
4-51(在串联电路中,已知,,,求频率C,30,FRLCR,20,L,0.1H
为和时电路的复阻抗,并说明何时阻抗为容性,何时为50Hz5000Hz
感性。
4-51(:、容性; Z,20,j74.76,f,50Hz
:、感性; f,5000HzZ,20,j3139,解:(1) f,50Hz
X,,L,2,3.14,50,0.1,31.4, L
11 X,,,106.157,C,6,C2,3.14,50,30,10
Z,R,j(X,X),20,j74.76,77.39,,75.02:, LC
为容性电路
(2) f,5000Hz
X,,L,2,3.14,5000,0.1,3140, L
11X ,,,1.06,C,6,C2,3.14,5000,30,10
Z,R,j(X,X),20,j3139,3139.06,89.63:, LC
为感性电路
159
第四章
4-52(图示串联电路中,已知,,,C,122,FRLCR,8,L,0.07H
,,,,,,,试求电路中电流,电压、和,UUUf,50HzIU,120,0:VRLC
CLR并画相量图。 i
,u,
习题4-52图
,,4-52(;U,106.64,27.25:V; I,13.33,27.25:AR
,,U,293,117.25:VU,348,,62.75:V;; LC
解: X,,L,314,0.07,21.98, R,8,L
11 X ,,,26.1,C,6,C314,122,10
? Z,R,j(X,X),8,j4.12,9,,27.25:, LC
, U,120,0:V
,U120,0:, ? I,,,13.33,27.25:AZ9,,27.25:
,,U,I,Z,13.33,27.25:,8,0:,106.64,27.25:V RR
,,U,I,Z,13.33,27.25:,21.98,90:,293,117.25:V LL
,,U,I,Z,13.33,27.25:,26.1,,90:,348,,62.75:V CC
,I ,UR,UL 117.25:
27.25: ,1,U62.75:,,U,U CL
,U C
160
第四章
4-53(在串联电路中,已知,,,电源电压X,15,X,5,RLCR,10,LC
,,u,102sin(314t,30:)V,求此时电路的复阻抗,电流,电压、UIZR
,,U和U,并画相量图。 LC
,4-53(;; I,0.707,,15:AZ,14.14,45:,
,,U,7.07,,15:V;U,10.605,75:V; RL
,U,3.535,,105:V; C
解: Z,R,j(X,X),10,j(15,5),14.14,45:, LC
, U,10,30:V
,U10,30:, ? I,,,0.707,,15:AZ14.14,45:
,,U,I,Z,0.707,,15:,10,0:,7.07,,15:V RR
,,U,I,Z,0.707,,15:,15,90:,10.605,75:V LL
,,U,I,Z,0.707,,15:,5,,90:,3.535,,105:V CC
, UL
,,U,ULC
, U
75:30:,115: 105:,UR ,,IUC
161
第四章
,4-54(如图4-10所示电路中,,保持不变,合上前后,电流X,48,USC
表()读数不变,求。 XAL
CRL ,
Su
i
,A
习题4-54图 4-54(X,24,; L
2222解: Z,R,XZ,R,(X,X)LC1L2
? 不变,也不变 IU
Z,Z? 12
2222? R,X,R,(X,X)LLC
22? X,(X,X) LLC
即 X,X,X 或 X,,(X,X) LLCLLC
取 X,,(X,X)X,2X 得 LLCCL
48XC? ,,,24,XL22
162
第四章
4-55(有两个复阻抗,相串联,接在电压Z,10,Z,4.47,63.4:,12
,上,求每一复阻抗两端的电压,并画出电压相量图。 U,100,0:V
4-55(;; 79,,18.43:V35.31,45:V,U2解: Z,10,Z,4.47,63.4:,,2,j412,45:U,1,18.43:
Z,Z,Z,12,j4,12.65,18.43:,12,U1
,U100,0:, I,,,7.9,,18.43:AZ12.65,18.43:
,,U,I,Z,7.9,,18.43:,10,0:,79,,18.43:V 11
,,U,I,Z,7.9,,18.43:,4.47,63.4:,35.31,45:V 22
4-56(有三个复阻抗Z,40,j30,,Z,20,j20,,Z,60,j80,相串123
,联,电源电压,试计算: U,100,30:V
(1)总的复阻抗; Z
,(2)电路电流; I
,,,UUU(3)、和,并画相量图。 123
,4-56((1);(2) I,0.67,,6.9:AZ,150,36.9:,
,,,U,33.5,30:VU,18.95,,51.9:VU,67,46.2:V(3);;; 123
Z,40,j30,,50,36.9:,解: (1) 1
Z,20,j20,,28.28,45:, 2
Z,60,j80,,100,53.1:, 3
Z,Z,Z,Z,120,j90,150,36.9:, 123
163
第四章
,U100,30:,(2) I,,,0.67,,6.9:AZ150,36.9:
,,(3)U,I,Z,0.67,,6.9:,50,36.9:,33.5,30:V 11
,,U,I,Z,0.67,,6.9:,28.28,45:,18.95,,51.9:V 22
,,U,U,29.01,j16.75,11.69,j14.91,40.7,j1.85,40.74,2.6:V12
,, U,I,Z,0.67,,6.9:,100,36.9:,67,46.2:V 33
S,UI,0.67,100,67VA
P,Scos36.9:,53.6W
Q,Ssin36.9:,40.2var
,,UU 3
,U 1
,,U,U30:122.6: 6.9:51.9:,1,I
,U2
164
第四章
4-57(如图所示,,,,电源电压为工频R,R,361,C,5.1,FL,1.9H12
,,,,求输出电压U、U和U,并画相量图。 380VABBCCA
Ai,,
R1 uCA
C CuABu L
u BCR2
,,B
习题4-57图
,,,4-57(U,380,0:V;U,367,,119:V;U,379,122.14:V; ABBCCA
,,U,380,0:V解: 设: U,380,0:VAB
,UCA11 X,,,624,C,6,C314,5.1,10
X,,L,314,1.9,596.6, ,LUAB
Z,R,jX,361,j624,721,,60:, AC1C
,UBCZ,R,jX,361,j596.6,698,58.8:, CB2L
Z,Z,Z,361,j624,361,j596.6,722,j27,722,,2.14:,? ABACCB
,U380,0:,I,,,0.526,2.14:A Z722,,2.14:AB
,,U,,I,Z,,0.526,2.14:,698,58.8:,,367,60.9:,367,,119:VBCBC
,,U,,I,Z,,0.526,2.14:,721,,60:,,379,,57.86:,379,122.14:V CAAC
165
第四章
,,4-58(如图所示电路中,已知,,,Z,5,j8,U,50,45:VI,2.5,,15:A1
Z1求。 Z2,,I
,Z2U
,4-58(; Z,25.8,78.83:,2习题4-58图
,U50,45:解: Z,,,20,60:,,10,j17.32,I2.5,,15:
Z,Z,Z10,j17.32,5,j8,Z122
Z,10,j17.32,5,j8,5,j25.32 2
Z,5,j25.32,25.8,78.83:, 2
-59(已知Z,3,45:,,Z,10,j10,,Z,,j5,相串联,如Z两端电41231
,压降为,求外加电压。 U27,,10:V
,4-59(; U,126.54,,25:V
Z,3,45:,,2.12,j2.12解: 1
Z,Z,Z,Z,2.12,j2.12,10,j10,j5 123
,12.12,j7.12,14.06,30:,
,U27,,10:1,I,,,9,,55:A Z3,45:1
,, ? U,I,Z,9,,55:,14.06,30:,126.54,,25:V
166
第四章
,4-60(三个复阻抗,,,与未知电压源成Z,5,j5,Z,,j8,Z,4,U123
,,串联电路。如上电压降为,求和。 ZIU63.2,18.5:V3
,,4-60(;; I,15.8,18.5:AU,150,0:V
,U63.2,18.5:3,解: I,,,15.8,18.5:A Z43
Z,Z,Z,Z,5,j5,j8,4,9,j3,9.49,,18.4:,123
,, U,I,Z,15.8,,18.5:,9.49,18.4:,150,0:V
4-61(为了确定负载阻抗Z,按图4-13电路进行实验。在开关闭合时,S2
加电压,得电流,功率,为了进一步确定U,220VI,10AP,1000W
负载是感性还是容性,可将打开,在同样电压下,得SU,220V
,功率。求Z、Z(已知为感性负载)。 ZI,12AP,1600W112
感性Z1A,W
SuVZ2
,
习题4-61图
Z,1.11,j34.2,Z,10,j19.6,-61(; 412
Z,1.11,j5.02,Z,10,j19.6,或;; 12
解:闭合时: SU,220VI,10AP,1000W
U220Z ? ,,,22,2I10
167
第四章
P1000 R,,,10,222I10
2222 ? X,Z,R,22,10,19.6, 222
,,打开时: I,12ASU,220VP,1600W
,P1600,? R,,,11.11,22,I12
, ? R,R,RR,11.11,10,1.11,121
U220 Z,,,18.33,,I12
2222,? X,Z,R,18.33,11.11,14.58,
X,X,,14.58,则: 12
? Z,(R,R),j(X,X) 1212
Z,R,jX Z,R,jX 111222
Z为感性,则X永为正, 11
X,X,,14.58,(1) 若 12
? Z,10,j19.6X,34.2,Z,1.11,j34.2 则 ? 211
X,X,,14.58,(2) 若 12
Z,10,j19.6X,5.02,Z,1.11,j5.02? 则 ? 211
168
第四章
4-62(如图所示,已知,,, ,端电压R,3,R,5,X,5,X,4,1L12C3
,,,,,,求各支路电流I,I,I及总电流,并画相量图。 IU,20,0:V123
i ,iii312
R1
uRX2 C3XL1
,
习题4-62图 ,,I,4,,53.1:AI,4,0:A4-62(;; 12
,,I,4,90:A;; I,6.45,7.13:A3
解: Z,R,jX,3,j4,5,53.1:, 11L
Z,R,5,0:, Z,,jX,5,,90:, 223C
,U20,0:,I,,,4,,53.1:A,2.4,j3.2? 1Z5,53.1:1
,U20,0:,I,,,4,0:A,4 2Z52
,U20,0:,I,,,4,90:A,j4 3Z5,,90:3
,,,,I,I,I,I,2.4,j3.2,4,j4,6.4,j0.8,6.45,7.13:A? 123
,,,II,I 323
, I
,1, 53.1:I2
,I1
169
第四章
,4-63(如图所示,,,,,求各支X,4,X,3.12,U,100,0:VR,3,LC
路电流和电路的有功功率,并作相量图。
, I,,,I 2I1R
, U,jXCjXL
,
习题4-63图 4-63(;;;; 32.05,90:A20,,53.1:A20,53.1:AP,1200W解: Z,,jX,,j3.12,3.12,,90:, 1C
Z,R,jX,3,j4,5,53.1:, 2L
,U100,0:,I,,,32.05,90:A? 1Z3.12,,90:1
,U100,0:,I,,,20,,53.1:A 2Z5,53.1:2
,,,I,I,I,32.05,90:,20,,53.1:,j32.05,12,j16 12
,12,j16,20,53.1:A
22P,IR,20,3,1200W 2
,I1
,I
,U,1
,I2
170
第四章
,4-64(如图所示,,,,,,R,5,X,10,R,12,X,16,U,50,0:V1C23L3
,试求两端的等值复导纳及。 IABY
,AI,
R3,jXC2,R1U
jXL3 ,B 习题4-64图
,4-64(; I,11.9,14.6:AY,0.238,14.6:S
,解: U,50,0:V
11 Z,R,0:,,5,0:, Y,,,0.2,0:S111Z5,0:1
Z,,jX,,j10,10,,90:,2C
11 Y,,,0.1,90:S,j0.12Z10,,90:2
Z,R,jX,12,j16,20,53.1:, 33L
11 Y,,,0.05,,53.1:S,0.03,j0.04 3Z20,53.1:3
Y,Y,Y,Y,0.2,j0.1,0.03,j0.04? 123
,0.23,j0.06,0.238,14.6:S
,,? I,U,Y,50,0:,0.238,14.6:,11.9,14.6:A
171
第四章
4-65( 如图所示电路中,当两个支路电流的相位差为时,,R,10,90:1
,,试求为多少, X,25,RX,8,C1L22
,
RR124-65(; R,20,2,U
jXL2,jXC1解法一: Z,R,jX,10,j2511C1,
习题4-65图
Z,R,jX,R,j822L22
, 设: U,U,0:
,UU,0:U,0:U, 则: I,,,,,68.2:A 1Z10,j2527,,68.2:271
,UU,0:U,I,,,,,, 2ZZ,Z,2
? ? 68.2,(,,),90:,,21.8:
88 ? ,tan,R,,20,2Rtan21.8:2
解法二:
Z,R,jX,10,j25,27,,68.2:, 11C1
,,,,90:,,21.8: ? 122
Z,R,jX,R,j8,Z,21.8:,Zcos21.8:,jZsin21.8: 22L22222
8Zsin21.8:,8 ? 求得: Z,,21.522sin21.8:
R,Zcos21.8:,21.5,0.928,20, 22
172
第四章
4-66(如图所示,一个线圈电阻,电感和一个电容R,10,L,30mH11
并联。已知,通过电容支路的电流C,20,F,,1000rads2
,,,I,2.5,0:A,求电流、I和等效复导纳Y,并画出相量图。 I21
i,i 1i2
R1 uC2L1
, 习题4-66图
,,I,3.95,,161.57:A4-66(;; I,1.75,,135:AY,0.014,45:S1
,3解: X,,L,1000,30,10,30, L
11 X ,,,50,C,6,C1000,20,10
Z,R,jX,10,j30,31.62,71.57:, 11L
11Y,,,0.032,,71.57:S 1Z31.62,71.57:1
Z,,jX,,j50,50,,90:, 2C
11Y,,,0.02,90:S 1Z50,,90:2
,0.01,j0.01,0.014,,45:S
,,U,I,Z,2.5,0:,50,,90:,125,,90:V 22
,U125,,90:,I,,,3.95,,161.57:A? 1Z31.62,71.57:1
,, I,U,Y,125,,90:,0.014,,45:,1.75,,135:A
173
第四章 4-67(一个晶体管集电极电路可看作如图所示具有电流源的电路,若
5,,,求。 i(t),2sin(2,,10t)mAC,100pFu(t)R,10,
54-67(; u(t),20sin(2,,10t)V
,11u(t)解: X,,,15923.57,RCC5,C2,3.14,10,100,
i(t)11 Y,,,0.1S1R10习题4-67图 115, Y,,,j6.28,10S2,jX,j15923.57C
,5 Y,Y,Y,0.1,j6.28,10,0.1S 12
,I2,0:m,? U,,,20,0:mVmY0.1
5? u(t),20sin(2,,10t)mV
174
第四章
,,,4-68(在图示的并联电路中,电流、和的有效值分别为、和III18A15A12
。求未知阻抗的和。 XR30AiL
ii12
4-68(;; X,4.39,R,5.13,L
R4,jX180:,,L解:
, I215,U, 18习题4-68图
30 ,I1
,I
, 设:的初相为零 U
,,I,15,0:A U,4,15,0:V2
22215,18,30 cos,,,,0.652,15,18
? ,,130.5:180:,,,49.5:
,I,18,,49.5:A? 1
,U60,0:Z,,,3.33,49.5:, 1,I18,,49.5:1
111Y,,,,0.195,j0.228 1RjX3.33,49.5:L
11 R,,5.13,X,,4.39,L0.2280.195
175
第四章
4-69(在并联电路中,跨接电阻的电压表读数为,求安培计读数为3,45V
,I多少, A,,,II12 V5,3,
,U4-69( 22.45A
j2,,j3,解: Z,5,j2,5.39,21.8:,1,
习题4-69图
Z,3,j3,4.24,,45:,2
,U,45,0:V 设: 2
,U2, ? I,,15,0:A23
,,U,I,Z,15,0:,4.24,,45:,63.6,,45:V? 22
,U63.6,,45:,I,,,11.8,,66.8:A ? 1Z5.39,21.8:1
,,,I,I,I,11.8,,66.8:,15,0: ? 12
,4.65,j10.85,15,19.65,j10.85
,? I,22.45,,28.9:A
? 安培表的读数为。 22.45A
176
第四章
,,4-70(在图示电路中,已知与同相,求。 XIUC
,I ,,I,186.6, 1,0:A,U,jXC4-70(; X,200,Cj50,
,
习题4-70图 解一:
(86.6,j50)(,jX)50X,j86.6XZ,ZCCC12Z,,, Z,Z86.6,j50,jX86.6,j(50,X)12CC
,,Z,Z,, 若与同相,则 ,,0IU
86.650,X,X22CC ? 86.6,50,50X ,C5086.6XC
? X,200, C
11解二: Yj Y,,0.0087,j0.005,12X86.6,j50C
1YYYj ? ,,,0.0087,(,0.005) 12XC
,,若与同相,则的虚部为零 IUY
1? ? X,200, ,0.005,0CXC
,,U,I,Z,1,0:,(86.6,j50),100,30:V解三: 11
, 相量图如图所示。 U,I,CIIC,sin30: I1
30:,I,Isin30:,0.5A IC11
U100X,,,200, ? CI0.5C
177
第四章
,4-71(在图示电路中,电路的并联部分端电压有效值为,求相应的的U50V
Z,8.5,30:,大小。 ,
20,
j6,,Uj60,,-71( 4U,112,,36.1:V
解: Z,20,j60,63.2,71.6:,1,
习题4-71图 Z,j6,6,90:,2
ZZ,63.2,71.6:,6,90:379.2,161.6:12Z ,,,,5.5,88.5:,12ZZjj,20,60,669,73.1:12
, 设:U,50,0:V 12
,U50,0:12,I,,,9.09,,88.5:A? Z5.5,88.5:12
Z,Z,Z,8.5,30:,5.5,88.5:,7.36,j4,0.14,j5.5 总12
,7.5,j9.75,12.3,52.4:,
,,U,I,Z,9.09,,88.5:,12.3,52.4:,112,,36.1:V? 总
178
第四章
4-72(图示电路中,,,求。 I,I,10AU,U,200VXL12C
,jXC
,,,I,I4-72( X,20,CICL,,,URjXU 1L2,
,,,解: U,200,0:V I,10,0:A2习题4-72图
U2002 R,,,20,I10
,U200,0:2002,I,,,,,90:A LX,90:X,90:XLLL
, I,10,,90:A ? X,20,LL
,,,I,I,10,j10,102,,45:AI,102,,45:A LC
R,jX20,j20L Z,,jX,,,jX,,,jX,10,j10 CCCR,jX20,j20L
22 ,10,j(10,X),10,(10,X),,CC
22,, ? U,I,Z,102,10,(10,X),,,45:CC1
22? 102,10,(10,X),200C
X,20,? C
,I,(,jX),200,200,,或者: CCu
(10,j10)(,jX),200,200,, 得: Cu
200,10X,j10X,200,, CCu
222(200,10X),(10X),200X,20, ? 求得: CCC
179
第四章
,,,,4-73(在图示电路中,已知,,求、、和U,200,0:VIII,,314rad/sab12
31.8mH5,a,,U。 cdiii12L16,6, cdu,,4-73(;I,20,,53.1:A; I,24,0:A1L25.5mH2398,F,,,I,20,53.1:A;U,192,90:V; 2cdb
习题4-73图 ,3解: X,,L,314,31.8,10,10,L11Z1
,,3X,,L,314,25.5,10,8, L22ZZ23
6110 X,,,8,C,C314,398,
Z,5,j10,11.2,63.4:, Z,6,j8,10,53.1:, 12
Z,6,j8,10,,53.1:, 3
,U200,0:ab,I,,,20,,53.1:A ? 1Z10,53.1:2
,U200,0:ab,I,,,20,53.1:A 2Z10,,53.1:3
,,,I,I,I,20,,53.1:,20,53.1:,12,j16,12,j16,24A 12
,,,U,,6I,6I,,120,,53.1:,120,53.1: cd12
,,72,j96,72,j96,192,90:,j192V
Z,Z10023Z,Z,,5,j10,,13.33,j10,16.67,36.9:, 1Z,Z1223
,,? U,I,Z,24,16.67,36.9:,400,36.9:V
180
第四章
4-74(图示电路中,网孔电流的参考方向选择如图,试列出网孔电流方程。
5 30ºV ,j2Ω 2Ω
10Ω I10 0ºVj5ΩI1 2
2Ω5Ω
,j2Ω I3 10 90ºV 10Ω
习题4-74图
,,,(7,j3)I,(j5)I,5I,10,0:4-74( 123
,,,,(j5)I,(12,j3)I,(2,j2)I,,5,30: 123
,,,,5I,(2,j2)I,(17,j2)I,,10,90: 123
,U,50,0:V4-75(在图示电路中,已知Z=Z=Z=Z=8+j6Ω,,1234s
,I,20,,30:AZ,求通过的电流。 s3
Z 3 Z1
IZZs 2 4
Us
习题4-75图
181
第四章
4-75( 7,151.1:A
-76(求电路中电压源的输出功率。 4
10Ω
3Ω
-j5Ω 50 0ºV j4Ω
习题4-76图
4-76( P,140.1W
4-77(对图示网络,求出A、B端的戴维南等效电路。
5Ω j5Ω A 3Ω 10 0ºV j4Ω
B
习题4-77图
,U,5.6,26:VZ,6.73,68.2:,4-77(、; OCi
4-78(对图示网络,求出A、B端的戴维南等效电路。
5Ω2Ωj3Ω A
55.8 -17ºV6Ω j5Ω
B 182 习题4-78图
第四章
,U,20,0:VZ,3.3,j1.4,4-78(、; OCi
4-79(已给电路中,求2Ω电阻中的电流。
j5Ω5Ω
50 0ºV50 90ºV 2Ω
习题4-79图
4-79( 13.74,,74:A
Z4-80(在给出的电路中,Z= Z= 3+j4Ω,Z= Z=4+j3Ω,Z= 2+j2Ω,求中132543
ZZ1 2 的电流。
Z10 0ºV3 20 90ºV
Z4
Z5
习题4-80图
4-80( 1.14,9.21:A
183
第四章 4-81(某厂取用功率为80k,,功率因数λ,0.65,负载呈感性,今需把电
路功率因数提高到0.9,问应并联多大电容。已知电源电压为380V,频
率为50H。 Z
4-81( 1208,F
4-82(如图,,其上电压 R,10,
* * A W 为,求电 u,283sin314tV
流与瞬时功率的解析式,若 ,R UV
用伏特表、安培表与功率表
测量时,读数为多少, 习题4-82图 4-82(;;; U,200VI,20AP,4000W
u,150sin(314t,15:)V4-83(一电阻与一电抗相串联,已知外加电压,
i,4.48sin(314t,45:)A电流,求电阻R与电抗X,说明是感抗还
是容抗。
Z,29,j16.74,4-83(;;;容抗; R,29,X,16.74,
,u,150sin(314t,45:)Vi,3sin(314t,15:)A4-84(已知,,求:(1)、U
,U,Z,I和;(2)画相量图;(3)求等效阻抗的和。 RL,I
,U,,Z,,25,j43.3,4-84((1)U,106,45:V;I,2.12,,15:A;; ,I
(3);; R,25,L,0.138H
184
第四章
cos,,0.8(,,0)4-85(某一负载为,,当一电阻炉与之并联时25kVA
(纯电阻),功率因素提高到0.85,求电阻炉的功率。 4-85(; P,4.2kWR
4-86(如图所示,无源二端网络端口处电压u(t)和电流i(t)分别如下所示,求
每种情况下的阻抗及导纳:
(1)u,200sin314t(V),i,10sin314t(A);
(2)u,10sin(314t,60:)(V),i,2sin(314t,15:)(A); u,100sin(10t,10:)(V)i,20sin(10t,40:)(A)(3),; u,8sin(2t,30:)(V)i,2sin(2t,60:)(A)(4),;
i(t)
N u(t)
习题4-86图
-86((1)4,; 20,0.05S
545,,0.245,,S (2),;
185
第四章
(3),; 530,,,0.230,S
(4),; 490,,0.2590,,S
4-87(如图所示电路,试确定方框内最简单串联组成的元件。
0.01Fi,10sin(2t,60:)(A) 2Ω N N u,100sin2t(V) u,100sin2t(V)
i,10cos(2t,150:)(A)
1H 3Ω2H
N N u,100sin(10t,60:)(V) u,30sin2t(V)
i,20sin(10t,60:)(A) i,5sin2t(A) 186 习题4-87图
第四章
4.87((1), R,,5CF,0.0577
(2), R,,3LH,29.33
(3), R,,3CF,0.125
(4), R,,5CF,0.01
4-88( 10μF电容器与25Ω电阻器并联,问当时需用多大的,,8000rad/s
电感与这一组合串联,使整个电路的电抗分量为0, 4-88( 1.25mH
4-89(如图所示电路,求输入阻抗。当时,是多少, Z(j,)Z(j,),,0
2Ω
1Ω
Z(j,) 1F
2H
习题4-89图
187
第四章
24(43),,,,jZ,4-89(, 3,()j,2,,j(21),,
4-90( 求图示电路的的表达式。当时,求它的等效导纳。 Y(j,),,2rad/s
2Ω
3Ω 1F 1H
习题4-90图
4-90( YS,,1.8981.47
4-91(求具有下列特点的功率因数:
(1) ; S,5000,j4000(VA)
(2) I,5.2(A),U,220(V),; Q,400var
Z,500(,)Q,0(3) ,I,4.8(A), ,; P,5kW
,I,10,40:(A)U,400(V)(4) ,,R,25(,); 4-91(,,, 0.780.9370.4340.625
188
第四章 4-92( 求具有下列特点的P、Q、S:
,,I,2,40:(A)U,450,70:(V)(1) ,;
,I,1.5,,20:(A)(2) ,; Z,5000,15:(,)
,U,200,35:(V)(3) ,; Z,1500,,15:(,)
-92((1),, 4779.4W450var900VA
(2),, 10866.67W2911.71var11250VA
(3),, 25.76W6.9var26.67VA
4-93(三相对称电源供给三台对称照明负载,负载有三种接法,(1)Y形有
Z,0中线(设),(2)Y形无中线,(3)Δ形。如果A相输送线上熔丝N
U,380V熔断,则各相负载上电压如何变化,设。 l
4-93(略
4-94(一台,相电压为220V的三相同步发电机供给对称的负载,25kVA
求下列两种接法满载时的线电压与线电流;(1)接成三角形;(2)接成星形。 4-94(形:,;形:,; ,Y220V65.6A380V37.9A
Z,(105,j60),4-95(每相阻抗为的负载,作Δ形连接,接在线电压为
Z,(2,j4),6600V电源上,每根输电线阻抗为。求负载相电流、
线电流,负载相电压,负载消耗的功率,电源供给的功率。
I,I,I,86.4AI,19.87A4-95(,; ABCP
P,828kWU,6030.8VP,784kW;;; SPZ
L,250,H4-96(一个收音机接收线圈的,,调节电容C,收听R,20,
189
第四章
的中央台,输入电路视为一RLC串联电路,求这时的电容值、720kHz
电路的品质因数? Q
4-96(, 195.6PF56.52
,44-97(在由,,所组成的串联电路中,C,588pFL,1.3,10HR,10,
U,5mV已知电源电压。求电路谐振时的频率、电路中的电流、元件S
L和C上的电压、电路的品质因数。
4-97(,,,, 575.94kHz0.5mA235mV235mV47
4-98(一串联谐振电路的特性阻抗,,100,,已知其谐振时的
,,1000rad/s,求元件参数L和C 。 o
4-98(100,F, 0.01H
4-99(如图所示,已知,可变电容为12pF~290pF,求谐振L,0.5mH
频率范围。欲使最低谐振频率为,试问应并联一只多大的电400kHz
C容。 x
LR
C x C
习题4-99图
4-99(,, 418kHz2055kHz26.9PF
190
第四章
4-100(如图所示电路中,一实际电感线圈与一电容器串联,已知
,当调节外加电压的频率为时发生谐振,此时CF,0.4,1000Hz
IA,1.1U,而电容上的电压为外加电压的倍,求电感线圈的11.10CO
和值。 RL
, I
,
C
R
,U L
,
习题4-100图
4-100(, 35.86,63.39mH
L,200,HC,450pF4-101(求通过,及所组成的串联电路的R,40,
通频带。
4-101( 31.84kHz
f,600kHz4-102(串联谐振电路的谐振频率,电阻,欲使电路R,10,o
191
第四章
的通频带,求电路的品质因数、电感和电容。 QLB,10kHzC-102(,, 4442PF600.159mH
4-103(一个电阻为、电感的线圈与的电容100pFR,13.7,L,0.25mH
器分别接成串联和并联,求各自的谐振频率和谐振阻抗。 4-103:,, 1000kHz13.7,182.48k,
4-104(在简单并联电路中,一支路为RL串联,另一支路为纯电容,已知
6,,5,10rad/sZ,2k,,Q,100,谐振阻抗。求、和。 RLCoO
4-104(,6H,0.01,F ,0.2,
4-105(有一线圈,其电阻,与C并联,组成RLC并联电路。已R,20,
Q,500知电路的品质因数,求电路的谐振阻抗和特性阻抗。 4-105(, 5M,10k,
Z,10k,4-106(一线圈与一电容器并联,已知发生谐振时的阻抗,O
C,200pFQ,,求线圈的电阻和电路的值。 RL,0.02mH
4-106(, 10,31.62
192
第四章
,U,20,0:VR,10k,4-107(如图所示电路中,,,设并联电路谐振时,Si
8,,10rad/sZ,R使谐振阻抗,这时阻抗匹配,,, Q,100ooi
I求(1)、和;(2)谐振时电流。 LRC0
i
Ri R
C L us
习题4-107图
1,H4-107(,,, 1,100PF1mA
R4-108(RLC串联电路,已达谐振状态,若将并联在电容两端,如图7-21所示,问是否改变电路的工作状态。
RL
C R 1
习题4-108图
193
第四章
4-108(略
C4-109(电感线圈在高频时需要考虑匝间分布电容,其等效电路如图7-3g
CC所示,现为了测量电感与匝间电容,用一电容与线圈并联,Lg1
f,6MHzC,10pFC,20pF当时,谐振频率,而当时,011
f,5MHzC,求和。 L01
R
CC,g 1 U
L
习题4-109图
31,F12.73,F4-109(;;
194