Dieu kien cong huang - BotroKienthucLuyenthiDaihoc- 123docz.net

Z , . Z c ô L o . ~ ô c o = ^ o f =

2 7 1 V L C O T = 2 7 I V L C IằU

Z z , = I Z c o S L c . = S-i

He qua cua hien tuong:

coC

2 *

I --==>p , =r- R = — t ' ' ô '

' i i i . i x - ' c o n g _ l u H ) n g ' m a x R

tan cp = 0 =>(p = 0 ne n u = U R , i : cung pha :

V i du 1: Cho doan mach RLC noi tiep co gia t r i cac phan t u co d i n h . Dat vao hai dau doan mach nay mot hieu dien the xoay chieu co tan so thay doi. K h i tan so goc cua dong dien bang COQ thi cam khang va d u n g khang co gia tri 20 Q va 80 Q. De trong mach xay ra cong huong, phai thay doi tan so goc cua dong dien den gia t r i CO bang

A . 2 COg . B. 0,25 COQ . C. 0,5 C O Q . D. 4coo.

trphtSn thUc V$t It LTDII Ht'ni hcnh VTV2, t^p 2 - Chu VMii isk-ri

Huong dan Z[ = W ( , L = 2 0( a ) L = 2 0

(i)C = 8 0 ( Q ) = > C =

8 0 W n

De xay ra cong huang: w = 1 1 • = 2cUn •Chon A.

/20 I ,v. 'y. ,„

I w,) 80o)()

V i d u 2: M o t cuon day c6 dien tro thuan 100 (Q) va c6 do t u cam l/n (H), noi tiep voi tu dien c6 dien d u n g SOO/TI ().iF). Dat vao hai dau doan mach mot dien ap xoay chieu tan so 50 (Hz). De dong dien trong mach cung pha v o i dien ap ta phai ghep noi tiep voi tu C mot tu C i c6 dien d u n g la bao nhieu?

A. 500/K (|,iF). B. 250/Tt (laF). C. 125/7t (^iF). D. 50/7t (^iF).

De (p = 0 thi Zc + , = Z, => — + = coL => C, = — ( i - i F ) => Chon C.

V i d u 3: Cho doan mach dien xoay chieu gom cuon day thuan cam L, tu dien C va bien tro R mac noi tiep. Khi dat vao hai dau mach mot dien ap xoay chieu on d j n h c6 tan so'f thi thay An^i'^hC = 1. K h i thay doi R thi

A. dien ap hieu d u n g gii>a hai dau bien tro thay doi. , B. tong tro cua mach van khong doi.

C. cong suat tieu thu tren mach thay doi. ^, , D. he so cong suat tren mach thay doi. :i , , , ,

Hu6iig dan

Tir dieu kien 4TI^FLC = 1 suy ra Z L =ZQ, tuc la trong mach xay ra cong 'U,^ = U = khong doi VR

hirang va liic nay :

Z = 7 R ' + ( Z | - Z e f = R

^7 I -y

=> Z thay doi P = -

R P thay doi • Chon C.

cos(p = —• = 1 = khong doi VR R

V i d\ 4: Doan mach xoay chieu RLC mac noi tiep, dien tro thuan cua mach R = 50Q. K h i xay ra cong huong d tan so'fi thi cuong do dong d i f n bang 1 A . Chi tang tan so cua mach dien len gap doi thi cuong do hieu d u n g trong mach la 0,8 A . Cam khang cua cuon day khi con 6 tan so fi la

A . 2 5 Q . B . 5 0 Q . C. 37,5 Q. D. 75 Q.

Huo^tg dan - Khi f = f, thi Z c , = Z L J va U = U K = IjR = 50 ( V ) .

C t r Tiyilll MTV D VVn Khang Vi^t

j^hi f = 2 f, thi Z L 2 = 2 Z L ,

^50- + 2,25.Zr, =•

7 - -

>Z|, = 2 5 ( Q )

= ^ v a Z, = V R^ . ( Z , , - Z c , ) ^ = ^ Chon A. ô• -,1 ,),v'.<i:i.)..i

hay V - - • • • 0,8

V i du 5: ^^9* doan mach AB gom hai doan mach A M va M B mac noi tiep. Doan mach A M gom dien tro thuan Ri mac noi tiep voi tu dien c6 dien d u n g C , doan mach M B gom dien tro thuan R2 mac no'i tiep v o i cuon cam thuan c6 do tu cam L. Dat dien ap xoay chieu u = Uocoscat (Uo va co khong doi) vao hai dau doan mach A B thi cong sua't tieu thu cua doan mach AB la 85 W. K h i do LCCO^ = 1 va do lech pha giira UAM va UMB la 90". Neu dat dien ap tren vao hai dau doan mach M B thi doan mach nay tieu thu cong sua't bang: ^n^, A . 8 5 W .

B. 135 W.

c. n o w .

D. 170 W.

A /

Dat dien ap vao AB :

Dat dien ap vao M B :

U ' R .

Z , , = Z c = ^ P = Huong dan

R, + R 2

U ) , 1 ' , v> J I I I - ( I j f <

tantpAM tancp^B = - 1 - Z c Z L

= - 1 ^ Z L = R i R 2

P' = R2 = U - R , R ; + zi R2 + R , R 2

= P = 85(W)=^Chon A.

Ri + R2 A Chu y: Neii cho bicii thuc u, ui. hoac uc ta dnh dime do lech pha cua u vai UL hoac

uc. Mat khdc ui. sani han i la KI2 va uc tre han i la TT/I ; tie do suy ra (p.

V i d u 6: M o t mach dien xoay chieu gom mot tu dien C noi tiep v o i m o t cuon day. Dat vao hai dau doan mach mot dien ap u = U V2 coscot (V) thi dien ap hai dau tu dien C la u ^ = U N/2 cos(a)t - 7t/3) (V). Ty so gii>a d u n g khang va cam khang bang - •

A. 1/3. B. 1/2. C. 1. D.2. x^^^^m

Huang dan

V i I luon luon som han la n/2 va theo bai ra U som han UQ la n/3 nen

^ tre pha han I la 71/6, tuc la (p = - — .

Do do :tan(p = Z , - Z R 6^ = t a n — = > R = ( Z , - - Z L ) > / 3 > 0 . V e L/

Dua vao bieu thuc u va uc suy ra: U A B = ^ A B = ^^Y R ^ + ( Z L - Z c f = Z c = > 2 ( Z c - Z L ) = Z c = > Z c = 2 Z L = > C h o n D .

6 tri? Men thitc V$t li LTDH tren htinli Vli2. l.,p J - Chu VSn BlSa

i du 7: Mot doan mach xoay chieu noi tiep AB gom dien tro thuan R, cupn cam thuan L va tu dien c6 dien dung C. Dien ap giiia hai dau doan AB la:

u = Uo>/2 coscot (V) thi dien ap tren L la U L = Uo N/2 cos(cot + 7t/3) (V). Muon mach xay ra cong huang thi dien dung ciia tu bang

A . C ^ . B. 0,750 C0,5C. D. 2C.

' Huang dan

Vi 7 luon luon tre pha han f/, la n/2 va theo bai ra U tre pha han U^^ la n/3 nen U som pha hon / la TC/6, tiic la cp = —.

tancp = ^i^— 5^ = t a n - ^ R = ( Z L - Zc) V3 > 0 R

U L = 72UAB =^ Z L = ^/2^/R + ( Z L - Zcr =^ Z L = 2.2(ZL - Z C ) => Z L 3 ^

De xay ra CQng huang thi ffq.p;^<

d 1 4 1 3 _

Z ' c = Z L = > Z ' C

3 ^ — = i — C = - C => Chen B.

(oC 3coC 4

i du 8: Mot doan mach noi tiep gom cuon cam thuan, tu dien va dien tro R.

Dat vao hai dau doan mach dien ap xoay chieu c6 gia tri hieu dung 120V thi cam khang cuon cam la 25Q va dung khang cua tu la lOOQ. Ne'u chi tang tan so dong dien len hai Ian thi dien ap hieu dung giiia hai dau dien tro R la A. 0 V. B. 120 V. C. 240 V. D. 60 V.

• Humgdan I ZL =COL = 2 5 ( Q )

Z c = - ^ = 100(Q) Z ' , = Z c

(i)'=2(o

Z'L =a)L = 50(Q)

Zc =

(oC = 50(Q)

Xay ra cong hudng => UR = U = 120(V) => Chon B.

du 9: Mot doan mach noi tiep gom cuon cam thuan, tu dien va dien tro R.

Dat vao hai dau doan mach dien ap xoay chieu c6 gia tri hieu dung U thi dung khang gap bon Ian cam khang. Neu chi tang tan so'dong dien k Ian thi dien ap hieu dung giiJa hai dau dien tro R la U. Gia tri k bang

A. 0,5. B.2. C.4. ^ D.0,25.

Huong dm j\ f f Z r =4ZT 1 -4coL=^LC- 1

coC 4(0^

U R = U => Xay ra cong hicdng => co'L ••

1 1

(o'C - = > L C - (0

.2 • co' = 2(0 => Chon B.

CO" 4(0

CM y: Neu cho Met = nL/C thi = nZj^Zc vd Ua' = H U L U C •

Cty Tjyftlf JVTVDVV/f Khang V/ft

V i dv 10: Mot doan mach AB mac noi tiep gom: dien tro thuan R, tu dien c6 dien dung C va cuon cam thuan c6 do tu cam L thay doi dugc. Dat vao hai dau doan mach AB dien ap xoay chieu 100 V - 50 Hz. Dieu chinh L de R 2 = 6,25L/C va dien ap 6 hai dau cuon cam lech pha so voi dien ap o hai dau doan mach AB goc n/2. Dien ap hieu dung a hai dau cuon cam la A.40(V). B. 30(V). C.50(V). D. 20 (V).

Huong dan t/| sdm pha h0n dong dien I la —

{/L lech pha vdi la. —

Cling pha vdi dong dien I

• Cong hiCcfng •

=6,25—= 6,25a)L. = 6,25Z[ .Z^ =6,25ZL =>Z^ = 0 , 4 R t oil rvvf- C coC

=^ U L = 0,4UR = 4 0 ( V ) => Chon A.

Chu y: Tir dieu kien cong huang de tinh cdc dien dp, ta van dung cdc cong thuc sau :

2 , T2

U^c = + U ^ ; U ' = (UR + U,f + ( U L ^ U C ) '

U?, = U^uf,;U^,e = U ^ ( U , , - U c f ^

L,R C

R C

.ằ i l l \il-J>. - j , . . ^ ; ... J / J .

V i du 11: Mach gom cuon cam va tu dien c6 dien dung thay doi dugc mac noi tiep roi mac vao nguon xoay chieu u = 100 V2 coscot (V), co khong doi. Dieu chinh dien dung de mach cong huang, liic nay hieu dien the hieu dung 2 dau cuon cam hang 200 (V). Khi do hieu dien the hieu dung giCra 2 ban hi la A. 100 V3 (V). B. 200 (V). C. 100 (V). D. 100 V2 (V).

Humgdan

' T 2 T , 2 . / T T I T \ . T T T T ^ ''^ M Ji'A LV^iH %St^i ii ' J • '

U, =Ur = + ( U L - U c f ^ UR = U = 100

Uld = + => 200^ = 100^ + =^ Uc = lOoVs (V) => Chon A.

V i du 12: Doan mach xoay chieu noi tiep gom dien tra thuan R, hi dien C va cuon cam Lr. Dat vao hai dau doan mach mot dien ap xoay chieu 120V - 50Hz thi dien ap giira hai dau doan R-C va dien ap giira dau doan C-Lr va co Cling mot gia tri hieu dung 90 V va trong mach dang co cong huang dien.

Dien ap hieu dung gifra hai dau tu dien la

A . 3 0 > ^ V . B . 6 0 V 2 V . C . 3 0 V 3 V . D.30V.

B d t r p klS'n t h i i c V^t II L T B t l t r i n k e n h VTV2. t^p 2 - Chu V^n B l e n

U L = U C

Huong dan

U2 = ( U K + U , ) ' + ( U L - U C ) ' = 1 2 0 2

Si I"

U K + U , =120 U , =90 Uf, + U^- = 90^

Uf^ + Uc = U r + ( U L - U c ) =90^

_ => Chon B. ' Uc =60V2(V) • • viiH

C/iii y; Tin' y; tn CQn<g hiani^ t h i hmn, Pimu, URIWIX. Dcxdc dinh xu the tang ginin, ta can cit vao phqm vi him thicn: cang gan vi tri cong huang thi I, P, UR cang Ian;

cang xa vi tri cong huang thi cdc dqi lugng do cang he. • • ^ '' •

V i du 13: Dat dien ap xoay chieu u = 220cosl007i:t (V) vao hai dau doan mach gom dien tro thuan 100 Q, cuon day thuan cam c6 do t u cam 1/K (H) va tu dien c6 dien d u n g C thay doi, mac no'i tiep. Neu thay doi dien d u n g C tu 200/7: (|iF) den SO/T: (|.iF) thi cuong do dong dien hieu d u n g qua mach A. giam. B. tang.

C. cue dai tai C = C2. j„ - D. tang roi giam.

•:yY;,. Huong dan ..X,..:})'T

* 1 ] 100 K h i mach cong huong: wL = — =>€„= — - = (f.iF)

Vi — ( 1 . 1 F ) > C„ > —( M F ) nen I tang roi giam => Chon D.

7t 71

^ Chuy:_ . . . : : , . . „ . ' ; • 1 . , ,

Khi mach R^LiCj xay ra cong huang ta c6: w^L,C, = 1 . Fo>'. Khi mach R2L2C2 xdy ra cong huang ta c6: w j L j C j = 1 . '•

50 100 200

*r ô X

Khi mach RiL^Cj noi tiep R2L2C2 xdy ra cong huang ta c6: wL, + wLj = + —!—

•• ' • ^ COC, 0)C2

Neu cho lien he L thi khu C: •

(L, + L 2 ) = co?L, +co^L2

Neil cho lien he C thi khu L:

2 1 7

©iLiCi = 1 = ^ — - = (OiLi : . . „ ; . . . : . : : , . ^1 1

ằ 2 L 2 C 2 — =

(oLj + (0L2 = + coCj a)C2

•Mf'/ < = • •

0)iL|Ci = 1 => L j = - 2 1

0)2L2C2 = 1 => L 2 = 1 CofC2

1 1

coL, + C D L 2 = - 7 r - + - 7 r

1 1

V<o?C, + ô 2 C 2 J CO C, C, Srt;( khi tun dinrc lien he cdc co ta suy ra lien hecdcfhoqc cdc T.

V i dy 14: H a i doan mach no] tiep RLC khac nhau: mach 1 va mach 2, cong h u o n g v o i d o n g dien xoay chieu c6 tan so goc Ian l u g t la coo va 2coo. Biet do t u cam cua mach 2 gap ba do t u cam ciia mach 1. Neu mac noi tiep hai doan mach dcS vc7i nhau thanh mpt mach thi no se cong h u o n g voi dong di^n xoay chieu CO tan so gocla ,„ ^ , ^ ,^ ^ , . , , ^ A. cooN/3 . B. l,5coo. C. coo7l3 . D . 0,5coo .

CO^I.2C2 = 1 C,

C- = co^L2 coL| + CO 1.2 = + • 1 1

' • • :.'t fifiifb •

' '•''^ O fclj'T> sit $tci • CO ( L j +1.2) = + CO2L2

wC, C0C2 aằb;3;wwti

cụ4L| =cụL, +4cộ3L| =^ co = 0,5cO()>/i3 => Chon D . Cft)?ôằi

V i dy 15: Mach xoay chieu R | , L [ , C | mac noi tiep c6 tan so'cong h u o n g f,.

Mach R 2 , L 2 , C 2 mac noi tiep ccS tan so cong h u o n g k. Biet C] = 2 C 2 va

= 2f|. Mac ncYi tiep hai mach do voi nhau thi tan so cong hucrng la A. f, V 2 . B. f,.

: b v >i ;<„.,.Ml <„vw Humgdan C 0 ? L , C, = 1 : : : > L , = - ^

CO2L2C2= 1 = ^ 1 . 2 = - ^ - co^C2

C. 2f, .

2co?C, wLj + C0L2 1 1

coCj C0C2 • CO

^to?C] 2co?Ci

1 2 • + —

C, • CO = coiV2

1 ^^"i^^/

=>Chon A. ' , ,

V i dy 16: Hai doan mach noi tiep RLC khac nhau deu cong h u o n g v o i dong dien xoay chieu c6 tan so f. Neu mac noi tiep hai doan mach do vc?i nhau thanh mt)t mach thi no se cong huong voi dong di^n xoay chieu c6 tan so la A. f. B. l,5f. C.2f. D.3f.

Huong dan

Ca hai doan mach ci:mg cc)ng huong v o i tan so f nen k h i ghep noi tiep chung C L i n g cong h u o n g v o i tan so'f Chon A. j .

Botrpkien thitc V^t li LTDH tren henli VTV2. t^p 2 - Chu Van Bien

2) Dieu ki#n I^ch pha

* Tren doan mach khong phan nhanh chi chua cac phan t u R, L va C. Gia sir M , N , P va Q la cac diem tren doan mach do. Do lech pha ciia \Xy^^, upg so v6i dong dien Ian l u g t la: tancp^^fj = ^^^^ va tancppQ = ^'"^ .

* U M N U p Q k h i va chi k h i tancpMN tancppQ = - 1 ^ PQ ^ _^

V i du 1 : (DH-2010) M o t doan mach AB gom hai doan mach A M va M B mac noi tiep. Doan mach A M c6 dien tro thuan 50 Q mac noi tiep v a i cuon cam thuan CO do t u cam I / K (H) , doan mach M B chi c6 tu dien v o i dien d u n g thay doi duoc. Dat dien ap u = UocoslOOrct (V) vao hai dau doan mach AB.

Dieu chinh dien d u n g ciia tu dien den gia trj Cj sao cho dien ap giua hai dau doan mach A B lech pha 7i/2 so v o i dien ap giira hai dau doan mach A M . Gia t r i ciia Ci bang

A. 40/71 (laF). . B.80/7r(nF). C. 20/7i (^F). D . 10/7i(^F).

Huang dan , v ZL=coL = 100(n) X l f i u ' l , <:I'.,it'

, r , , Z L - Z C Z L , 1 0 0 - Z c 100 ,

V i u 1 U A M nen: t a n c p . t a n m . v i = - 1 => — ^ = - 1 => ^ . = - 1

R R 50 50

=>Zc =125(Q)=>C = ^ — = -.10"^(F)=>ChonB. i ,H iofi i-^f/

V i du 2: Cho doan mach xoay chieu mac no'i tiep theo diing t h u t u gom cuon cam thuan c6 do t u cam L = 4/K ( H ) , dien tro thuan R va tu dien c6 dien dung C = 0,l/(7r) (mF). Ne'u dien ap hai dau doan chua RL vuong pha vai dien ap hai dau doan chua RC thi R bang

A. 30 Q. , B. 200 Q. C. 300 Q. D . 120 Q.

Huong dan

tan (PRI . tan (PRC = - 1 => • — ^ = - 1 => R = J — = 200 (Q) => Chon B.

Chu y: Ncu 92 - cp, = A(p thi tan ((p2 -^>^) = = tan ^^P 1 + tancpj tan(pi

V i du 3; Dat dien ap xoay chieu vao hai dau doan mach AB gom hai doan mach A M va M B mac noi tiep. Doan A M gom dien tro thuan R = 100>y3 Q mac noi tiep v o i cuon cam thuan c6 cam khang Zi., doan M B chi c6 tu dien CO d u n g khang 200Q. Biet dien ap giCra hai dau doan mach A M va dien ap giij-a hai dau doan mach AB lech pha nhau 7c/6. Gia trj Zi. bang

A . 5 0 V 3 Q . B. lOOQ. C . I O O V S Q . D. 300 Q.

•IPP' tancpAM

Huong dan

- f t 1 ' ' :

R I O O V 3 Z L - Z c _ Z L - 2 0 0

t a n c p A B = — 1 0 0 V 3 . , , . . , ,

Vi dien ap giira hai d a u doan m a c h A M v a dien ap giiia hai d a u doan m a c h AB lech p h a nhau 71/6 nen suy ra cp^^ - cp^H = - >1v|.;i!:;M'J:>ằTS.':t';yrii

tancpAM -tantpAB _ • ''^ 200.100N/3 1 Cdch 1: • = tan — => 71

l + tancpAMtancpAB 6 (lOOVs )^ + Z ^ - 200ZL ^ Z L - 200ZL - 30000 = 0 => Z L = 300(Q) Chon D.

Cdch 2: T h u 4 p h u o n g an ta nhan thay chi p h u o n g an D la d u n g , mi |

300 71

tancpAM- ^ - ^ 0 0 ^ ^ 0 0 ^ 3 Z L - Z C _ Z L- 2 0 0 _ 300-200

tan cpAB = R = = - c p A B -

9 A M - 'PAB =

V i du 4: M o t doan mach dien xoay chieu gom cuon day c6 dien tro 100 Q mac noi tiep vol tu dien c6 dung khang 200 Q. Ne'u do lech pha cua dien ap giiia hai dau cuon day va dien ap giiia hai dau doan mach la 57i/12 thi cam khang ciia cuon day bang

A. 1 0 0 ( 2 -V 3) Q h o a c l 0 0 V 3 Q. B.IOOQ.

C. lOOVSQ. r D. 300Qhoacl00N /3a '

Huang dan ''

/•I Z L '

~R ~ Too rt'i'Ji''"*''

Z, - Z r Z L -2 0 0 •''"'^^

100 •••^iiacn.l.srcy^* f ^ i - ^ A I'Jr.

Cdchl: Zc = — = 200(0);

coC

tan (pAM = tancpAB =-

57t tan(p(,£] - tancp 12 1 + tan (Pcd tan (p = tan-

R 571

I :

12 Z 100

L Z L- 2 0 0

100 1

100• 100

• zl - 200ZL + 10000 (2V3 - 3 ) = 0 Z L =100V3(Q)

• Chon A.

Z L = 1 0 0 ( 2 - 7 3 ) ( Q ) '

^dch 2: K h i di thi ne'u lam theo each 1 se mat nhieu thoi gian de giai p h u o n g trinh bac 2! De khac phuc kho khan nay ta diing p h u o n g phap t h u true tiep bo'n p h u o n g an.

Buoc 1: V o i Z L = 1 0 0 Q thi cpAM = 7t/4 va cpMB = -7t/4 => khong d u n g .

Bd trp kiSn tbiic V$t It LTOHtri ,i h<nli 1 11 J. I.ip J ( Ini VMn Bten

Bu-oc 2: V a i Zi, = 100 Q thi c p A M = 7t/3 va cp.viB = -7r/12 => diing.

, Buoc 3: V o i Zi. = 300 Q thi khong hop ly.

Buoc 4: Ke't luan chon A.

V i d u 5: Dat dien ap xoay chieu on djnh vao hai dau doan mach mac no'i tiep g o m cuon day co dien tro thuan R, co cam khang 150 Q va tu dien co dien d u n g C thay doi dugc. K h i d u n g khang Zc = 100 Q va Zc = 200 Q thi dong dien trong mach co pha ban dau hon kem nhau TC/3. Dien tro R bang

A . 50 V3 Q. : • B. 100 Q. C. 100 V3 Q. D . 50 D . . v- - Huong dan

Z , - - Z c , 50 ^ / -50 ^

Cdch 1:

tancp2 =

- tan — ] + tan tan cp] 3

50^50 j , , . , . . . -

= V3 => R = 50^/3 ( n ) => Chon A.

R R ,.,,V

)'• a ; '' .''1 'tVi

Cdch 2:

tan<pj = tancpj =

•/POX \vMh &-f,ni n'.j^::h )bll ;|i '

R Z L - Z^^2 - 5 0

R R :0, !i()f

(|)| =-

(P2 = - -

R=50V3(Q)=>Chon A.

V i d u 6: Su d u n g m o t dien ap xoay chieu on d i n h va 3 d u n g cu gom dien tro R, tu dien C, cuon cam thuan L. K h i mac Ian l u g t hai doan mach noi tiep RC

? hoac RL vao dien ap noi tren thi cuong do dong dien tiic thoi trong hai t r u o n g hop lech pha nhau 27t/3 va co cijng gia t n hieu d u n g 2 A . K h i mac , doan mach noi tiep RLC vao di^n ap noi tren thi gia trj cuong do dong dien

hieu d u n g trong mach la ' \

A. 4 A B. 3 A C. l A

Huong dan

D. 2 A

Ii = I , => ZRL = ZRP => Z , =RC Zr =>

tanipi =

tan = • R

-Zr

<r>i -V2 = 2jt ="C1 = -(|>2

R Z i = Zc = RV3

U = I , Z K , = 2 7R ' + Z ^ = 4 R

=>] = u u

V R ^ . ( Z , - Z C ) ^ " R

= — = 4 ( A ) => Chon A.

V i d u 7: Doan mach xoay chieu gom cuon thuan cam L , noi tiep voi dien tro R.

Dien ap xoay chieu hai dau mach chi tan so goc co thay d(>i ducjc. Ta thay co 2 gia trj ciia co la co^ va CO2 thi do lech pha cua hieu dien thegiCra hai dau doan mach v o i dong dien Ian lugt la (pi va (p2. Cho biet cpi + 92 = n/4. Chon he thuc dung:

A. ( c o i+ C 0 2) R L = R 2 _ L2 , B. (cO|+CO2)RL = R 2 + CO1CO2L2.

C. ( C O ,+ ( 0 2) R L = R2 + 2o),(02L2, D. (co, + (02) R L = R^ - 2c,),co2 L^.

jlf^.:. , Huong dan •

tancp, =

co^L

R W2L

'PI +i|>2 = " tiin(p| +t.in<P2 1- t.in . tnn (pT =1

R R = 1 -(0|L CO2L

R • R

Ami-11^^-

=> (o), + CO2 ) L R = R~ - coiUjLr => Chon A. , •„ .. .,,

V i d u 8: Cho mach gc^m tlien trci thuan R, tu dien C va cuon day thuan cam L mac no'i tiep. VtVi cac gia t r i ban dau thi cuong do hieu d u n g trong mach dang CO gia trj I va dong dien / som pha n/3 so v o i dien ap ;( dat vao mach.

Neu ta tang L va R len hai Ian, giam C d i hai Ian thi I va dc) lech pha giua va se bien doi thenao? ,5.) 1-">IS^;

A. I khong doi, do lech pha khong doi , yUuA^i rod? imt mli WM) ^ n l . n ' - B. I giam V 2 Ian, do lech pha khong doi dsSm i-^tfe : I '

C. I giam 2 Ian, do lech pha khong dcii ,:Q,-fC>r*>

D. I va do lech pha deu giam ;n oSv

Huotigdan 'Ifi 'V'^'v .. mi •J&ui=! gno*) rttx'' :'

1 =

R- 1

coC Td/i/,' liva L len 2 Ian va giam C 2 Idn

coL-

tan (p = • (oC

R = tan — = -^/3 3

\\ 2 Idn

< ., => Chon C.

Do lech pha khong doi

Bo trfi kicn thiic V^t li LTDH tren hcnh VTV2, t^p 2 - Chu VSn BiBn

I , M , li J , i.1 I >U : ,>) t 'I ' >i

Huang dan r.