I D. dien ap hieu d u n g tren tu giam.
*• , . : : r . Huang dan ^.-UJA <d nM> >:/''-'••:
i T u : C0(2 < COR < COL (khi co = coc thi Ucmnx, khi co = COR thi URnwx (cong huc^ng),
f khi CO = COL thi Utmav) ta nhan thay, t u vj tri co = COR giam tan so mot l u g n g nho thi CO djch ve phia coc mot lugng nho tiic la Uc se tang Chon C. thi CO djch ve phia coc mot lugng nho tiic la Uc se tang Chon C.
Bo trg hicn tluic V^t li LTBII tren h€nh VTV2. t^p 2 - Chu VMn Bigti
V i d u 7: N h a n xet nao sau day la SAl? Trong mot mach dien xoay chieu c6 RCL m3c noi tiep dang c6 cgng huong, néu ta tang tan só m a v a n gjf, nguyen dien ap hieu d u n g cua nguon dien xoay chieu dat vao mach t h i : Ạ Dien ap hieu d u n g U K giam.
B. Dong dien trong mach tro nen cham pha hon dien ap dat vao mach RCL. C. Dien ap hieu d u n g tren doan R noi tiép voi C se tang.
D. C u o n g do hieu d u n g trong mach se giam.
Huwig dan
1
Luc dau ZQ = = 0)L = Z L => I = max; = max (oC
Sau do tang co thi
=> Chon C. '
I = — giam dan;U|{ giam dan
1 Z, - Z r
ZQ = — < coL = Z L =J> tan(p = — — > 0 =^ u sSm pha hdn i o)C
U K C = I J R ' +
R
Mi '
V i d u 8: Dat mot dien ap u = Uo cos cot (Uo khong doi, co thay doi dugc) vao hni dau doan mach gc'5m R, L, C mac noi tiep thoa man dieu kien CR^ < 2L. Goi
V i , V2, Ian l u g t la cac von kémac vao hai dau R, L, C. K h i tang dan tan so
t u gia tri 0 thi thay tren moi von ke deu co mot gia t n cue dai, t h u t u Ian
lugt cac von ke chi gia trj cue dai khi tang dan tan sóla
A . Y i , V 2 , V 3 . B . V 3 , V 2 , V i . C. V 3 , V i , V 2 . D . V i , V3,V2. - ' • • • O r : , ' . . - . . . / . ; r- ' ' v \ • • ^ • • ' . • • ^ H u d v g d a n - ' • • • O r : , ' . . - . . . / . ; r- ' ' v \ • • ^ • • ' . • • ^ H u d v g d a n
l a m c h o f/c mnx ' o ' " max => Chon C.
Chu y: NcU hai todn chi cho
CO him thicn tie coi deii coi tlii de fun ^iii tri Ian nhat nho
nhat ta so $a)ih gid tri tqi hai
dau giai hqn va gid tri tqi dinh.
lam choUi^^ax
V i d u 9: Dat dien ap xoay chieu u = 100 V2 coscot V v o i co thay doi tir IOOT: rad/s den 2007t rad/s vao hai dau doan mach noi tiep gom d i ^ n tro R = 80 N/2 0,
cugn cam thuan v o i do t u cam I/TC H va tu dien co dien d u n g O/i/rt mF. Dien ap hieu d u n g giij-a hai dau cuon cam co gia t r i Icjn nhat va nho nhat tuonj^ iVng la
190 ' '
Cty TNHllMTVDVv'HKhang Vift
Ạ 107,2 V v a 88,4 V. C. 50 V v a 100/3 V. U w L coL - 1 ^ B. 100 V v a 50 V. D. 50V2 V va50 V. Huong dan = , - ^ -5: ^ = 6 0 ( Q ) C 2 2 U , „ „ , o Z c = Z , =60Q=>co = : : r ^ = - ^ ^ ~ 1 6 6 , 7 T t ( r a d / s ) ' co = 1007r=>U, = CO = 20071 => U , = Z,-C 3 100.100 « 8 8 , 4 ( V ) + ( 1 0 0 - 1 0 0 ) ' 100.200 " 50071 (0 = 80N/2)" + ( 2 0 0- 5 0 ) ' 100.500/3 80V2)' + ( 5 0 0 / 3 - 6 0 ) ^ K 1 0 6 , 4 ( V ) = 1 0 7 , 2 ( V ) ,. ' ' / . { - . . ,.
b. Khi (0 thai/ dot qim hai gid tri wt va (02 va cdc dieu kien khdc lit • }
Khi 0 ) thay doi hai gia tri coi va C02 ma co cung I , UK, P thi Li>.,x, URmnx, Pmnx khi
COn = JCOICOT = ; = » 0 3 i L I = — J - A 7 ; ^
" ' ^ N/LC VCO, 0)ICVCO2 M C C02
Bay gio neu cho them dieu kien: ^ = n^R^ t h i
Z a = R CO-
Z L I = R In COi
•3; rif>
CO2
V i d u 1 : Cho mach dien xoay chieu RLC mac noi tiep, cuon day thuan cam. Biet L = C R l Dat vao hai dau doan mach dien ap xoay chieu c^'n dinh, mach
CO Cling he so cong sua't voi hai gia trj cua tan so goc SOTI rad/s va 200K
rad/s. He so cong suát cua doan mach bang ' ' '
Ạ 2/713. B.1/2. CAI42. 0.3/^12. .'1 • Huang dan ^••V'''' R R coscpi =coscp2 <=> R 2 + cọL - I • coiL CO] cojC \2 V C o),CJ \ R 2 + (09L - 1 (OTC ^ = Z a , | ^ = , / ^ . T h a y i ; = ^ R ' thi: CO, (02 V C 191
kien thiic V^t //' LTDII tren kenh VTV2. t^p 2-Chu VSn BiSn • C O S C p i = • R R2 + R r ^ - R p C02 V « i ; 2 VT3 => Chon Ạ
V i d u 2: Cho mach dien xoay chieu RLC mac noi tiep, cuon day thuan cam.
Biet L = CW. Dat vao hai dau doan mach dien ap xoay chieu on dinh, mach c6
cung he so cong suat 0,35 * 3/N/73 voi hai gia tri ciia tan so goc (Oi = IOOTI rad/s va C02. Gia tri C02 C O the la
Ạ 507trad/s. ,:: B. IOOTT/S rad/s. C. lOOn/? rad/s. D . 1007t/9 rad/s.
Huongđn R R _ 1 C O S 9 ] = cos 92 <=> R2 + cojL 1 •=>LC = - R2 + C02L - - 1 (O1CO2 Thay L = CR^ thi dirge: — = R
;l ... 1/ Thay C = L/R2 thi duac: C0]L = R
= > C O S = • |R2 + R / ^ - R I ^ 0)2 (0, 1 + IOOTC (02 C02 TOOTT -\ >/73 CO2 =90071 IOOTI =>ChonẠ , j - , • - „ ^ - r ; ) ( 0 2 = - - — ^^^^^ „
Chil y: Dieu kien ^ = n^R^ cd thctrd hinh dual dang dieu kien vuong phạ
V i d u 3: Dat dien ap u = 125 N/2 coscot (V), co thay doi dugc vao doan mach noi tiep A M B . Doan mach A M g o m dien tro R noi tiep t u dien, doan mach M B chua cuon day c6 dien tro r. Biet dien ap tren doan A M luon v u o n g pha voi di§n ap tren doan M B va r = R. V o i hai gia t r i co = IOOK rad/s va co = 56,25:: rad/s t h i mach A B C O cung he so cong suat va gia t r i do bang ® Ạ 0,96. B.0,85. C . 0,91. D . 0,82. Huang dan L = C R2 U A M J - U M B =>tan(pAM tan (p^B = - 1 => - ^ = - l = > R r C = - R^ = > C O S ( | ) i = • = 0,96 (R + r f + (1)2 \1 4 + 0), ©2 0)2 0)1 Chon Ạ
Chti y: ^hi cho biet cam khang, dung khang khi co = coi va khi co = ^02 mach cong
•.(.(f'J'c:- ( x 5 i ) Q 0 r \: . huvng thi = 0)2 That vqy: ±LL 1 Z c , = - ( o f L C - a)iC Cong hudng o ft)2L : Zci 1 0)2C 0), 1 IO2 -LI
Vi d u 4: Doan mach R L C khong phan nhanh mac vao mang dien tan so coi thi cam khang la 20 (Q) va d u n g khang la 60 (Q). Neu mac vao mang dien co tan so 0)2 = 60 (rad/s) thi cuong do dong dien cung pha v o i dien ap 0 hai dau doan mach. Gia t r i 0)1 la | i
Ạ 20 ^/6 (rad/s). B. 50 (rad/s). C. 60 (rad/s). D. 20 S (rad/s).
Huang dan
Z c i =
Z 1 1 => o)i L C = — ^ . V i u va i cung pha nen 0)2L = — r L C =
a),C 0)1 = 0)2
- C I
-CI
^ L l ^ (,oj—= 20>/3 (rad/s) Chon D. 60
a)2C
/ still'''
Jill , , J
©2
Vi d u 5: (DH-2011) Dat dien ap u = U >/2 cos2Ttft (U khong doi, tan so f thay doi
dugc) vao hai dau doan mach mac noi tiep gom dien tro thuan R, cuon cam thuan CO do t u cam L va tu dien co dien dung C. K h i tan so la fi thi cam khang
va dung khang cua doan mach co gia trj Ian lugt la 6Q va 8Q. Khi tan so la ii
thi he so cong suat cua doan mach bang 1. He thiic lien he giua fi va h la ' A . h = 2(^/ 7 3 .5 • B. h = 0,5fi V3 . C. f2 = 0,75f,. D . ta = 4f,/3.
./^K*: Huong dan
CO, [ Z [ 7 fi /6 . 2fi ^, '
= . / - = : > t2 = - j = => Chon Ạ CO, V -CI
BS tr^ klSn thtic V^t li LTDH Ircn henh VTV2. t^p 2 - Chii l<df» Bicn
V i d v 6: Cho doan mach RLC noi tiep, dat vao hai dau doan mach dien ap
u = Uocos(27Tft) (V) vcVi f thay doi dugc. K h i f = 75 H z t h i tháy cuong do
d o n g dien hieu d u n g trong mach cue dai va cam I<hang Zi, = TOO il. K h i tan
so CO gia t i i fii thi tháy d u n g khang Zc = 75 Q. Tan so f la
. , A . 50 V2 H z . B. 75 V2 H z . C. 75 H z . D . 100 H z .
Huottg dan
1
K h i f = 75 H z thi mach cong huong: Z^ = 100 = ZQ •= 1507:C
K h i f = fo thi d u n g khang: 75 = Z' c = 1 27Tf C 100 f
f = 100(Hz) =>ChonD. 75 75
V i d u 7: Mach dien xoay chieu KLC mac noi tiep ctien trtr thuan 100 D, cuon
thuan cam c6 d o t u cam L = 2>/3/TI ( H ) . Dat vao hai dau doan mach mot dien ap xoay chieu u =U(.cos2nft, f thay doi dugc. K h i f = 50 H z thi i cham pha Ti/3 so vtVi ụ De i cung pha voi u thi f c6 gia trj la
A . 4 0 H Z . B . 5 0 V 2 H z . C. 100 H z . D . 25 V2 H z . ' M , Huong dan 1 27tfL 27TfC tancp = R Cong hitang : f = fo = n tan — = • 3 1 • 200 S - 100 1 27tVLC (2V3 10-^ 7tV3 = 2 5 v / 2 ( H z ) =>ChonD. i : ;C/»M2/;' ^ ' ,s , „„
Khi thay doi ta)i no ma lien quan den tinh dien np thi ta ap dung cCmg thíec tinh dien dp tong clio liai trwang Iigjv
* Luc dau: = + ( U , - U ^ ) " tinh duoc U vn Zị = liiR, Zc = foR.
* Neil f ' = nf tin Z'l. = nZị = ul<iR, Z'c = Zdii = k-R/n hay ÚL = nkiÚn va U'c = ' kiU'Rln. Thay ccic hieu ihux do vao phuviig tniili: U " = uf^ + (U ' L - U'e)^ thi clii
con an duy nhat la U'n.
V i d\ 8 : D a t dien ap xoay chieu u = UN/2 cos27tft ( V ) vao hai d a u doan mach noi tiep g o m dien t r a R , cuon cam thuan L va t u dien C thi d i ^ n ap hieu d u n g tren R, tren L va tren C Ian lugt la 136 V, 136 V va 34 V. N e u chi tang tan so ciia nguon 2 Ian thi dien ap hieu d u n g tren dien tro la
Ạ 25 V . B . 5 0 V . C. 5 0 V 2 V . D . 80 V.
194 '
Cty TISHH nrv DVVH KhangVlft
Huong dan U = 7 U R + ( U L - U C ) ' = 7 ^ 3 6 ^ ( 1 3 6 - 3 4 ) ' = 1 7 0 ( V ) r Z ' L = 2 Z L = 2 R : = > U ' L = 2 U ' R U , = U , . U,, ^ Z L = R „ R =^ Z r = — f' = 2f: 4 ^ 4 Z' r = thay vao = U i + ( U ' L - U ' c ) dugc 170^ =Úf^ + 225Úf^ 64 ÚK = 8 0 ( V ) =j.ChonD.
C\xu y: Khi cho biet hai gia tri coi va 02 ma I i = I2 = Imox/n t h i Z i = Z 2 = nR hay R2 +
COiC;
\ CO2L -
ro2C = nR
Neu 0)1 > m thi chi c6 thexay ra trwang hóp:
c),L - = RVn^ - 1 imt
C02L — = - R V n 2 - l
" 2 C , y „
T u he nay c6 the d i theo hai huang: * Neu cho biet L ma khong biet C thi khir C :
c o j L - ^ = coiRVn^ - 1 _ ^ \
=>\ n-M =^L(o)?-a)^) = R V n 2 - l ( c a i+ ( 0 2) = > R = - ^
7 1 I 2
CO2L = - ( 0 2 R V n - 1 ^ 'fcl)''.;: ...v^ •
Neu cho biet C ma khong biet L thi k h u L : 1 R N / U ^ - I L - co^C CO, 1 RV.7^ « 2C CỎC 1 1 — + — C02 C0i0)2Cvr?-l
Vi d u 9: Dat dien ap xoay chieu c6 tan so w thay doi dugc vao hai dau doan mach RLC noi tiep. K h i co thay doi thi cuong do hieu d u n g trong mach dat gia tri cue dai la L.ux va hai gia trj un va L02 t h i cuang do hieu d u n g trong
mach dat gia trj deu being I„ux/Vs . Cho (cji - i02)/{Cio\co2) = 60 Q, tinh R. A . R = 30Q. . , . B.R = 60Q. C . R = 120Q. D . R = 100Q.
i " Thay gia trj vao cong thuc R -
Huang dan
(cO| - 0)2) _ 60
0)10)2 cVi^ > / 5 ^ = 30(Q) =>ChonẠ j
Bo tifi hlén thirc V^t li LTDI1 tren kenh VTV2. t^p 2 - CIiu Van BlSn
V i d u 1 0 : ( D H - 2012) Dat dien ap u = Uo coscot (V) (Uo khong d o i , o) thay doi duoc) vao hai dau doan mach gom di§n tro thuan R, cuon cam thuan c6 do tu cam 0,8/71 H va t u dien mSc noi tiép. K h i co = coo thi cuong do dong dien hieu d u n g qua doan mach dat gia tri cue dai I m . K h i co = w i hoac co = co2 thi cuong do d o n g dien cue dai qua doan mach bang nhau va bang I m .
Biét CO 1 - C02 = 20071 rad/s. Gia trj ciia R bang ,,, v .
Ạ 150Q, B. 200Q. C. 160Q. D . 50 Q.
Huattg dan
Y C L i a bai toan, k h i co = coi hoac co = co2 thi I i = h = Inwv/ .
Sau khi nghien cuu ki p h u o n g phap noi tren, thay gia trj vao cong thuc: 0,8
R =
.20071
= 160(Q) InchonC. ; i
5. Mot so dau hieu chung khi L, C va co thay doị
ạ Dien ap hieu dung tren doan LrC cite lieu ,\\
LrC 7 r^ + ( Z L - Z c f 7(r + R f + ( Z L - Z c y = m m « Z L - Z e =0 va U L r C m i n = U r + R U. , c / "
Do thi phu thuoc Uịrc theo (ZL - Zc) co dang n h u hinh ben.
Z L - Zc = 0 ^ U LrC mill u-r + R :) • " ,1 ' t>>,J
Z L - Zc ==oz:>UịrCmax = U
V i du 1 : Dat mot dien ap u = 120 V2 cosl007tt (V), (t do bSng giay) vao hai dau doan mach ncYi tiép g6m dien tro 20 Q, cuon day co dien tro thuan 10 Q, chi etc) t u cam L thay doi va mot tu dien C. K h i L thay d o i gia trj cue tieu cua dien ap hieu d u n g hai dau doan mach g6m cuon day noi tiép vai tu dien C la , A . 60 V2 V. B. 40 V. C. 40 72 V. D . 60 V. Huang dan U L r C = I Z . . c ^ = U r ' + ( Z L - Z c r LrC = m m = U 0^ 7(r + R ) ^ + 0 2 n)j ' i i J fii;'. -=40(V) ^ ( r + R ) 2- f( Z L - Z c f
V i du 2: Dat mot dien ap u = 12072 cos27rft (V), (t do bang giay) vao hai dau doan mach noi tiép gom dien tro 80 Q, cuc}n day co dien tro thuan 16 Q co do t u cam 0,2/7i H va mot tu dien co dien d u n g C = 1/K mF. K h i chi thay dó
I
f thi thay dien ap h i f u d u n g giiia hai dau doan mach g o m cupn day noi tiép voi tu di#n C
Ạ dat gia trj cue tieu la 20 V.
B. dat gia t r i cue dai la 20 V. C. tang k h i f tang.