Dat vao'hai dau doan macin mot dien ap xoay chieu c6 gia tri hieu dung U khong doi va dieu chinh R = .Ro de cong suat tieu thu trcMi nicich dat cue dai.. Dieu chinh tri so dien tro R de
Trang 1V i du 10: M o t cuon day c6 dien tro thuan R = 100 N/S Q va do t u cam L = 3/^
(H) Mac noi tiep voi cuon day mot doan mach X c6 tong tro Zx roi mac vao
hieu dien t h e x o a y chieu c6 hieu dien t h e h i e u d u n g la 120 V, tan so 50 Hz
thi thay dong dien qua mach nhanh pha 30" so voi hieu dien the hai dau
doan mach X va c6 gia trj hieu.dung 0,3 A Cong suat tieu thy tren doan
mach X la bao nhieu? „ j
Ve gian do vec to cho doan A M truoc, roi ve
tiep doan M B tre pha hon dong dien la 30"
Ta nhan thay A A M B vuong tai M nen:
6 0 V 3 /
A" 120 V
Ux = M B = ^120^ - (60>y3)' = 60(V)
Px = U x l c o s i p , = 60.0,3.cos30" = 9^/3(W) =^ Chon C
Binh luan: Sau khi fun dime MB sc tun dime ;^6c a roi gdc (p va P = UJcoscp
V i du 11: Cuon day c6 dien tro thuan R va do t u
cam L mac vao dien ap xoay chieu u =
250N/2 coslOOTct (V) thi dong dien qua cuon day
CO gia t r i hieu d u n g la 5 A va lech pha so voi
dien ap hai dau doan mach la 7t/6 Mac noi tiep
cuon day voi doan mach X thi cuong do hieu
d u n g qua mach la 3 A va dien ap giira hai dau /
cuon day v u o n g pha v o l dien ap gii>a hai dau X ^ ':30^^'""
d u n g C i Doan mach M B gom dien tro R2 mac noi tiep voi tu dien c6 dien
d u n g C2 K h i dat vao hai dau A, B mot dien ap xoay chieu c6 gia t r i hieu
d u n g U thi dien ap hieu d u n g gii>a hai dau doan mach A M la U i , con dien
ap hieu d u n g giua hai dau doan mach M B la U2 Neu U = U i + U2 thi he thuc lien he nao sau day la dung?
A C i R i = C 2 R 2 B.CiR2 = C2Ri C C i C 2 = R i R 2 D CiC2RiR2= 1
Huong dan
U = U | + UT =>(P| = => tancpi = tanq)2 coC, R,C, = R , C 2^2 Chon A
G i a tri tu'c thoi
-a Tinh gin tri tux thai dim vao bicu thi'rc Khi lien quan den gid tri tue thai cm u va i thi truac tien phdi vie't hieu thuc ciia cac dai luang da truac ^
V i du 1: Bieu thuc cua dien ap giua hai dau doan mach la u = U()cos(1007it +
n/4) (V) Biet dien ap nay som pha n/3 doi voi cuong do dong dien trong
mach va c6 gia tri hi^u d u n g la 2 A Cuong do dong di^n trong mach khi
t = 1/300 (s) la
A 2 V2 (A) B 1 (A) C V3 (A) , D 2 (A)
121
Trang 2300 12
= 2 ( A ) = ^ C h o n D
V i d u 2: Clio mot mach dien khong phan nhanh gom dien tro thuan 40/^/3 Q,
c u o n day t l i u a n cam co do t u cam 0,4/7i ( H ) , va m o t t u d i e n co d i e n d u n g
l/(87t) (mF) D o n g dien trong mach co bieu thuc: i = I(icos(1007rt - 2n/3) (A)
1 T a i t h o i d i e m ban dau d i e n ap g i i i a hai d a u d o a n mach co gia t r i - 4 0 V2 ( V )
V i d u 3: D a t d i e n ap xoay chieu u = U()cos(1007ct — n/2) (V) (t d o b a n g giay) vao
hai d a u d o a n mach no'i tie'p g o m t u dien co d i e n d u n g C = 0,2/n (mF) va
d i e n t r o t h u a n R = 50 Q H o i sau t h o i d i e m ban dau (t = 0) m o t k h o a n g t h o i
gian ngan n h a t b a n g bao n h i e u t h : dien tich tren t u d i e n bang 0?
D o u tre pha h o n i la 7t/4 m a uc tre h o n i la n/l nen uc tre pha h a n u la 7r/4
D o do: UQ = UQ(2 C O S lOOjtt
Giti tri ti'tc thai lien qiian dm xu hitang tang giiim
^ po'i v a i bai l o a n d a n g nay t h o n g t h u o n g l a m nhu- sau:
* Viet b i e u t h u c cac d a i l i r o n g co lien quan; ' ' i « JJV ; ; i
* Di.ra vao V T L G va xu h u o n g tang g i a m de xac d j n h (cot + cp) (tang t h i n a m
n u a d u a l V T L G , con g i a m t h i 6 n i i a tren);
* Thay gia trj cua cot vao bieu thuc can t i n h
V i d y 1= doan mach gom cuon day co dien tro thuan R va cam khang Zi = R mac noi tiep vcVi tu dien C mot di^n ap xoay chieu, d i ^ n ap hieu d u n g g i u a hai dau day va gifra hai ban t u d i e n Ian l u p t la Ud = 50 (V)
va Uc = 70 (V) K h i dien ap tiVc t h o i giira hai ban tu d i ^ n co gia t r i uc = 70 (V)
va dang tang t h i d i e n ap tiVc t h o i g i i i a hai dau cuon day co gia t r i la
= 0 Chon A
V i d y 2: D a t vao hai dau d o a n mach g o m cuon day co d i e n t r o t h u a n R va cam khang Z L = R^/3 mac no'i tiep v o i tu d i e n C m o t d i e n ap xoay chieu, d i e n ap hieu d u n g g i u a hai dau day va giCra hai ban tu d i e n Ian l u o t la Ud = 50 (V)
va Uc = 70 ( V ) K h i d i e n ap tufc t h o i g i u a hai ban t u d i e n co gia t r i uc = 35 >/2 (V) va d a n g g i a m t h i d i e n ap tuc t h a i giiJa hai d a u c u p n day co gia t r i la
Trang 3c Cgni^ cac ^in tri ti't'c thai (ton^ Iiap aic dao dong dicu hoa)
Ta can phan biet gia trj cue dal (Uo, lo luon duang), gia tri hi^u d u n g ( U , I
luon d u o n g ) va gia trj tuc thoi (u, i c6 the am, duong, bSng 0):
U5 = u,^K + ( U , „ - U o c f ; = + ( U L - U c ) ' ; u = u,, + u^ + uc
2c
V i d u 1 : Mach dien xoay chieu khong phan nhanh gom dien tra thuan R, cu6n
cam thuan co cam khang Zi, va tu dien c6 d u n g khang Zc = 3 Z i Vao mot
thoi diem khi hi^u dien the tien dien tro va tren tu di?n c6 gia tri tuc thoi
t u o n g u n g la 40 V va 30 V thi hi^u dien thegiCra hai dau mach dien la
A 55 V B 60 V - ^•'-'.•^ C 50 V ^'"'• D 25 V
Thay u,^ = 40(V), = 30(V) va u, = - u ^ — = -10(V) vao he thiVc:
u = U R + U | + U c => u = 40 + (-10) + 30 = 60(V) => Chon B
V i d u 2: Mach dien xoay chieu khong phan nhanh g o m di^n tro thuan R, cuon
cam thuan co cam khang Zi va tu dien c6 d u n g khang Zc = 3ZL Vao mot
thoi diem dien ap hai dau doan mach va tren cuon cam co gia trj tuc thoi
tuong irng la 40 V va 30 V thi dien ap tren R la ,,
Chti y: NcU A, B, C tlwo di'ini^ ihi't tir la ba diciu trcn doan mach dicn xoay ch
khong phan nhanh va bic'u thi'ec dicn ap tuc thai trcn cdc doan mach AB, BC livi
heat la: UAB = Uoicosicot + cpi) (V), unc = Uo2cos(cot + (pi) (V) thi bic'u tlii'ec dicn lip
trcn doan AC la UAC - UAU + UBC
ICII
• • fit I
Cdch 1:
02 • 2 U „ , U o 2 C O s ( ( p 2 - ( p , ) ' ' ^ * ' ^ ' " ' tan(p = U Q I ' ^ ' " ^ ! + U ( ) 2 ^'"'P2
U()| cos(pi + U()2 C O S 9 2
•(13 rrf
V i d u 3: Cho doan mach xoay chieu khong phan nhanh A , B, C la ba diem tren
doan mach do Bieu thuc dien ap tuc thoi tren cac doan mach A B , B C Ian
luot la: U A i i = 60cos(100Kt + n/6) ( V ) , U B C = 6 0 c o s ( ] O O K t + 27t/3) ( V ) Dien
ap hieu d u n g giira hai diem A , C la
NB la U N B = 50N/2 sin(1007it + 57x/6) ( V ) Bieu thuc di^n ap tuc thoi giua hai dau doan mach A N la f^o-, t i ^-^^^ - > ' J
A U A N = 150 72 sin(1007it + 7i/3) ( V ) B U A N = 150 V2 cos(1207xt + 7i/3) ( V )
va C D Ian l u o t la: ui = 400 V2 cos(1007tt + n/4) (V), U2 = 400cos(1007it - n/2)
(V), U 3 = 500cos(100nt + n) (V) Xac d i n h dien ap cue dai giOa hai diem A, D
A 100>/2V B.IOOV C 2 0 0 V D 2 0 0 V 2 V
nf.>; u * i Hiiongdan V
u = u, + U 2 + U 3 =coscot(Ai coscp, + A 2 C o s ( p 2 + )-sincot(Ai sincp, + A j sintpj + - )
u = cosl007tt 40074 cos - + 400 cos — + 500 cos T:
-sinlOOnt 40074 sin - + 400 sin — + 500 sin n
= -100cosl007tt(V) = 100cos(1007ct + 7t)(V) => Chon B ^ {nlutii nif- ;
Cdch 2: u = 4 0 0 7 2 Z - + 4 0 0 Z - - + SOOZjt = -100 'ith iftrf o mdl 3^,;.<j{^.n'}-'
=^u = -100cosl007rt(V) = 100cos(100;tt + 7t)(V) ' ' U ' , ^ • ^ ^
=>ChonB
V i d u 6: Dat di?n ap u = Uocos(1007it + 77i/12) (V) vao hai dau doan mach A M B
thi bieu thuc dien ap giiia hai dau cac doan mach A M va M B Ian luot la
U A M = 100cos(1007it + 7t/4) (V) va U M B = Uoicos(1007tt + 37t/4) (V) Gia trj Uo va
Uoi Ian l u g t la
125
Trang 4try KIS„ th^c V^t II LTBtl tren kcnh VTV2 t^p 2 - c„u l u n B u „
A IOOV2 V v a l O O V
C TOO V va 100 V2 V : D 200 V v a l O O V s V, B ^00^/3 V v a 2 0 0 V
Huang datt
Phirong t r i n h u = UAM + UMB hay ^ ,
Uo cosf lOOnt + ^ 1 = lOOcosf lOOnt + 12 + Ui„ cos I lOOnt + ~ j d u n g voi t
' D e tinh cac bien dp con lai thi ta c6 the chon cac t dac biet
Chon t = (s) thi
400 U() cos n 7n
4 "^12; = 100 cos + Ujo cos
C / i i i 1/: N(?M si'c di/n^v^ f^fl«/i f/zflo may tinli ton^ hap dao dong thi c6 the dim
, phuang phdp thu tumig doi nhanh
. v - i i u i i i c i c n uien xoay chieu K, L, C mac no'i tiep theo t h u t u d o (cupn
cam thuan) K h i d o dien ap hieu d u n g 6 hai d a u dien t r o R la 200 V Khi
dien ap tiVc t h a i a hai dau doan mach la 100^2 V t h i dien ap tiic thoi giiJ'''
hai dau dien t r o v a cuon cam deu la -100N/6 V T i n h g i a trj h i | u d y n g cu3
dien ap 6 hai d a u doan mach AB
tuc thai qua mach va bien d o dien ap tren R la UOR O thoi d i e m t, dien ap
tuc thai 6 hai d a u doan mach chua L C la ULC v a d i e n ap tuc thoi gi&a hai
dau d i^ n tro R la UK thi
A UOR = ULccoscp + URsincp B UOR = uucsincp + URCOScp
C (ui,c)2 + (uK/tan(p)2 = (UOK)^ D (UR)^ + (ui.c/tancp)^ = (UOR)2
0 V T a i thoi d i e m t2 cac gia trj tuc thai ui.(t2) = -10 72 V, uc(t2) = 5-j2V, UR(t2) = 15 72 V T i n h bien dp dien ap dat vao hai dau mach AB?
Trang 5Ba trp hicn thiic V^t li L TON tren kenli VTV2 tap 2 - Cliu V^n Bl&n
hai docin A M v a M B m a c n o i tie'p D o a n A M g o m t u d i e n c6 d i e n d u n g C
noi tie'p vcVi ctien t r o R v a d o a n M B c h i CCT cuc)n c a m c 6 d i e n trtV t h u a n r v a c6
d 9 tu' c a m L Bie't L = r R C V a o t h o i d i e m to, d i e n a p t r e n M B b a n g 64 V t h i
A U A M = 50cos(cot - 571/12) ( V ) ^ B U A M = 50cos(a)t - 7i/4) ( V )
C U A M = 200cos((ot - 7i/4) ( V ) D U A M = 200cos(a)t - 57t/12) ( V )
M
129
Trang 6Bo trp hie'n thiic V^t li LTDH tren k&nh VTV2 t^p 2 - Chu VHn BI6n
U A M =50 COS cot +
12 3
(V) Chon B
V i d u 8: M o t doan mach A B g o m doan A M va M B mac noi tie'p Doan A M g6n^
dien t r o R noi tie'p v o i t u dien C, con doan M B chi c6 cuon cam L Dat vao
A B m o t dien ap xoay chieu chi c6 tan so thay doi dugc thi dien ap tuc thoj
tren A M va tren M B luon luon lech pha nhau 7t/2 K h i mach coug huong thi
• d i ^ n ap tren A M c6 gia trj hieu dung U i va tre pha so v o i di^n ap tren AB
m o t goc a i Dieu chinh tan so de dien ap hieu d u n g tren A M la U2 thi dien
ap tvVc thoi tren A M lai tre h o n dien ap tren A B mot goc ai Bie't a i + aa = 7t/2
va U i = 0,75U2 T i n h he so cong sua't ciia mach A M khi xay ra cong huong
= tan a => a = P => cp = 2a - 90 • cos(p = sin 2a
V i d u 9: Doan mach xoay chieu A B g o m
hai doan mach A M noi tie'p M B Doan
mach A M g o m dien tro R noi tie'p v a i
tu dien c6 dien d u n g C, doan mach M B
CO cuon cam c6 do t u cam L va dien t r a
r Bie't R^ = r^ = L/C va dien ap hieu
d u n g giij-a hai dau M B Ion gap V3
dien ap hai d a u A M so' cong sua't
Vi R = r nen p = a = > cp = a + p - 9 0 " = 30" => coscp = 0,866 => Chon C
V i d u 10: M o t doan mach A B g o m doan A M va M B mac noi tie'p Doan A M gom t u dien C no'i tie'p v o i dien t r o R, con doan M B chi c6 cuon cam c6 dp tir cam L va dien tro thuan r = R Dat vao A B mot dien ap xoay chieu chi c6 tan so goc co thay d o i dugc thi dien ap tuc thoi tren A M va tren M B luon
luon lech pha nhau nil K h i co = coi thi dien ap tren A M co gia trj hieu d u n g
Ui va tre pha so v o i dien ap tren A B mot goc a i K h i co = C02 thi dien ap hieu
d u n g tren A M la U2 va dien ap tuc thoi tren A M lai tre h o n dien ap tren A B
mot goc ai Bie't a i + a2 = 7i/2 va U i = U2 Vs Tinh he so cong sua't ciia mach
ung voi COI va C02
Khi L thay doi deUum, thi 0,^^ 1 0 (URC va U la hai cqnh cm tain giac vuong dm
Uumx la cqnh huyen, UR la dumig cao thuoc cqnh huyen):
Trang 7&itfp kidit thvtc vai i(ii-hti tten k&nh VTV2 t^p2-chu van bleu
U K C V 2 UV2 = 1;
K/n' C thay dot dcUcmx tin 0,^, 1 0 (UKI va U la hai cqnh cua tamgidc viian^ con
Uomn la cqnh Inn/en, UK lii dicaiii^ cao thuoc cqnh hiii/cn): ^
U K L f r U f 1 1 1
UV2 = 1;
V i d u 11: Cho mach dien xoay chieu R, L, C m3c rioi fi#p theb t'HiVfe rfo (cuon
cam thuan) Dien d u n g C c6 the thay doi duoc Dieu chinh C de dien ap 6
hai dau C la ion nha't Khi do dien ap hieu d u n g 6 hai dau dien tro R la
100 V2 V K h i dien ap tuc thoi 6 hai dau doan mach la 100N/2 V thi dien ap
tu'c thai giua hai dau doan mach chi'ia dien tro va cuon cam la -100-76 V
Tfhh gia trj hieu d u n g cua dien ap 6 hai dau doan mach AB
De t i m gia trj Ion nhat va nho nhat cua mot dai l u g n g (Z, I , UK, U I , Uc, UMN,
P ) khi CO mot yeu to bien thien thong thirong lam theo cac buck sau:
Budc 1: Bieu dien dai hrgng can tim cue trj la mot ham cua bien so thay doi (R,
Zi., Z t , w) •'
Buo'c 2: De t i m max, m i n ta thuong dung: 6at dang thifc Cosi (tim R de Pni v)
hogc tam thuc bac 2 (tim (o, Zi, de Ui n iv, tim co, Zc de Ucmnx) hoac dao ham
khao sat ham so de t i m max, m i n (tim Zu de UKI n.ix, t i m Zc de UKCI.I.IX) Rieng
doi voi bai toan t i m Ui ni v khi L thay doi hoac tim Ucn,.ix khi C thay doi thi c6
the d u n g gian do vec to phoi hop vdi djnh l i ham so sin
Mot bai toan c6 the giai theo nhieu each nhung thuong chi c6 mot each hay
va ngcin gon Vi vay, nen tranh tinh trang "Diiiii^ dao mo trail dccat tict ga"
Nell a, b la hai so dirarig thi \;> •AiisW sit^ •i^ni^i K\U ,\v:iky;is\ i\\
a + b > 2 VaTb (a + b),„i„ = 27i:b a + b *^^u " = " xay ra khi a = b , \|,
Khi tich 2 s o k h o n g doi, tong nho nha't khi 2 so bang nhau
Khi tong 2 so khong doi, tich 2 so Ion nha't k h i 2 so bang nhay
Dao ham khao sat ham so
Ham soy = f(x) c6 eye t r i k h i f'(x) = 0
Trang 8oa ttffRieh tHiTc v^mt^Tunrren Kcnn vi vj, t^p j - una van men
V i d u 1: (DH-2008) Doan mach dien xoay chieu g o m bien tro R, cuon day
thuan cam c6 do t u cam L va tu dien c6 di§n d u n g C mac noi tie'p Biet dien
ap hieu d u n g giiia hai dau doan mach la U, cam Ichang Zi., d u n g khang Zc
(voi Zc ^ ZL) va tan so dong dien trong mach khong doi Thay doi R den gia
trj Ro thi cong suat tieu t h u cua doan mach dat gia trj cue dai P,n, k h i do
A Ro = Zi + Zc B Pm = U2/R() C Pm = Zi,VZc D Ro = |ZL - Zc|
=>ChonD
V i d u 2: Cho mach dien noi tie'p gom cuon cam thuan do t u cam 0,2/n (H), tu
dien CO dien d u n g 0,l/7t (mF) va bien t r a R Dien ap dat vao hai dau doan
mach d i ^ n ap xoay chieu on d j n h c6 tan so f (f < 100 Hz) Thay d o i R den gia
trj 190 Q t h i cong suat tieu t h u tren toan mach dat gia trj cue dai Gia t r i f la
= 3 0 , 5 ( Q )
V i d y 3: M o t doan m a c h xoay chieu mac no'i tie'p g o m tu C = 50/7i (jiF); cuon cam t h u a n c6 d o t u cam 0,8/7i (H) va bien t r a R Dat vao hai dau doan mach dien ap u = 200cosl007Tt (V) (t d o bang giay) De cong suat tieu t h u cua mach cue dai thi gia t r i ciia bien t r a va cong suat cue d a i la
Vi d y 4: Doan mach d i ^ n xoay chieu g o m bien t r a R, cuon day thuan cam va t u
dien c6 dien d u n g IOO/TI (JIF) no'i tie'p Dat vao hai dau mach d i ^ n ap xoay
chieu 100 V - 50 H z Thay doi gia trj bien t r a t h i cong suat dat gia t r i cue dai bang 50 W D o t u cam cua cuon day c6 gia t r j :
A 71(H) B 1/7I(H) C 2 / 7 I ( H ) D 1,5/71 (H)
Hwang dan
2c = 1 coC Chon C
135
Trang 9Bo trp kicn tliiic V^t li LTOtl tren k^nh VTV2 tap 2 - Chu VSn Bi€n
cue dai trong ctoan mach la 200 W Khi R = 18 Q thi macli tieu thu cong sua'j
= 24(Q) i ' '
2.24 = 2 0 0 ^ U = 40V6(V)
9600.18 R^ ( Z L - Z c f 18^+24" y = 192(W) zoChonC
V i d u 6: Cho mach dien xoay chieu gom RLC mac noi tie'p Trong do, L = 0,2/?!
(H), C = I/TT (mF), R la mot bie'n tro voi gia tri ban dau R = 20 Q Mach difoc
mac vao mang dien xoay chieu c6 tan so f = 50 (Hz) K h i dieu chinh bien tro
de dien tro tang dan thi cong suat tren mach se:
A ban dau tang dan sau dcS giam dan B tang dan
C ban dau giam dan sau do tang dan D giam dan rrt aiioh jf>l' 1
li.thi'i unijh Jift-ij im 'jtyi /) Huang dan ^imtii (fb m (Kuril
61 Z L =coL = 2 0 ( Q ) ;
Zc = 1 = 10(Q)
coC
f^nx « R o = | Z | , - Z e | = 10(Q)
Luc dau R = 20 (Q), roi tang dan tiVi
cang ngay cang xa gia tri cue dai nen P
giam dan => Chgn D "* '"
V i d u 7: Cho mot doan mach RLC c6 R thay doi Dat vao'hai dau doan macin
mot dien ap xoay chieu c6 gia tri hieu dung U khong doi va dieu chinh R =
.Ro de cong suat tieu thu trcMi nicich dat cue dai Khi do dien ap hieu dung
•p tren hai dau ciia R l a 45 V Tinh dien ap hieu d u n g giua hai dau R khi dieu
4 U ' R =18VT0 * 5 6 , 9 2 ( V )
ma = , U i + ( U ' L - , U ' c r
• Chon A
1 3 6
V i d u 8: (DH-20(>8) Dat dien ap u = Uocosait (Uo va io khong doi) vao hai dau
doan mach RLC khong phan nhanh Bie't do tu cam va dien d u n g dugc giu khong doi Dieu chinh tri so dien tro R de cong suat tieu thu cua doan mach dat cue dai K h i do he so cong suat cua doan mcich bang
V i d u 9: Cho iri^ch dien xoay chieu noi tie'p gom bien tro R, cuon day thuan
cam CO cam khang 200 Q va tu dien c6 dung khang 100 Q Dien ap dat vao
hai dau d o t i n m a c h u = 100 N/2 coslOOnt ( V ) Xac djnh gia tri ciia bien tro de cong suat tieu thu tren doan mach la 40 W
A 100 Q hoac 150 Q B 100 Q hoac 50 Q ,t u 0.t •
C 200 Q hole 150 Q D 200 Q hoac 50,Q ii c,iO ;Vi'
| : , ^ 1 ff^: fjumig dan \/ Cfc&
P = I^R = U ^ R
R 2 + ( Z L - Z c r
•40 lOO^R R^ +100^
R , = 2 0 0 ( Q ) R2 = 5 0 ( Q ) > Chon p
V i d u 10: (DH-2009) Dat dien ap xoay chieu c6 g i a t r i hieu d u n g khong doi vao hai dau doan mach gom bien tro R mac noi tie'p voi tu dien D u n g khang cua
tu dien la 100 Q K h i dieu chinh R thi tai hai gia trj Ri va R2 cong sua't tieu thu cua dogn mach nhir nhau Bie't dien ap hieu d u n g giira hai dau tu dien khi R = R I bang hai Ian dien ap hieu d u n g giua hai dau tu ^ien k h i R = Rz-Cac gia tri R i va R2 la "y g f i V i P/> rhn-''-' lif'n U't*^ s.':^''
Trang 10fRi=50(Q) „ , : ,
=> => Chon C
R2 =200(Q)
V i du 11: Mot mach dien gom tu dien C, mot cuon cam thuan L va mot bien tro
R dugc mac no'i tiep
Dat vao hai dau mach dien mot di^n ap u = 100 V2 coslOOrtt (V) Khi de bien
tro 6 gia trj Ri hoac R2 thi cong sua't tieu thu tren doan mach la nhu nhau
Neu Ri + R2 = 100 Q thi gia trj cong sua't do bang , 1
2R„ ';y. r^firin ori-) 3#|i' r'
V i du 12: (CD-2010) Dat dien ap u = UV2coscot (V) vao hai dau doan mach
gom cuon cam thuan mac noi tiep vdi mot bien tro R Ung voi hai gia trj
Ri = 20 Q va R2 = 80 Q thi cong sua't tieu thu trong doan mach deu bang
400W Gia trj ciia U la
A 400V ' • = B.200V C.IOOV D.IOOV2 V
R, +R2 = ^ = > U = 7P(R, +R2) = 200(V)=>ChonB
V i du 13: Dat dien ap xoay chieu vao hai dau mot doan mach AB no'i tiep gom
bien tro R, cuon cam thuan va tu dien Thay doi R thi mach tieu thu cung
mot cong sua't ung voi hai gia trj ciia bien tro la Ri = 90 Q va R2 = 160 CI
so'cong sua't ciia mach AB ung voi Ri va R2 Ian lugt la J
Vi du 15: Cho mach dien xoay chieu noi tiep gom bien tro R, cuon day thuan
cam C O do tu cam 0,5/7c (H) va tu dien c6 dien dung 0,l/7t (mF) Dien ap dat
vao hai dau doan mach u = UA/2 coslOOTtt (V) Khi thay doi R, ta thay c6 hai gia trj khac nhau ciia bien tro la Ri va R2 thi cong sua't tieu thu ciia mach
deu la P Chon ke't luan dung
thu tren mach dat cue dai bang
139
Trang 11y i d v 17: M(?t maoh dien xoay chieu gom tu dien C, mot cuon cam thuan L vji
mot bion tro R duoc mMc noi tiep Khi R = 24 Q thi cong suat tieu thu tren
doan mach cue dai la 300 W K h i de bien tro 6 gia trj 18 Q hoac 32 Q thi
cong suat ticu thu tren doan mgch l^Vnhu nhau ya gia trj do bang
V i d u 18: Doan m a c h xoay c h i e u RLC noi tiep v o i R la bien tro K h i Ri = 40 U
hoac R2 = 10 U t h i cong suat tieu thu cua doan mach n h u nhau K h i R = R,,
thi c o n g suat tieu t h u cua doan mach dat gia tri Ion n h a t , va cuang do dong
d i g n q u a m a c h i = 2cos(1007it + K/12) (A) Dien ap h a i d a u doan mach c6 the
CO b i e u t h u c
A u =50^/2 cos(100Kt + 7rt/12) (V) B u = 50 V2 cos(100Trt - 5TI/12) (V)
C u = 40 V2 cos(1007it - 7i/6) (V) D u = 40cos(1007tt + K/3) (V)
Humg dan
TCr R1R2 = ( Z L - Z c ) ' = , R ^ =>Rp = V R ; R 7 = 20(Q)
Z = ^Ro + ( Z L -Zcf = 20V2Q =^ U(, = loZ = 40V2 c:, ,>|
Khi {p = - - = > u -40^/2cosf^OOnt+ — - - ] ( V ) ^^ i>
12 4 Khi (p = + - =0 u = 40>/2cos lOOjit + — + - ( V )
4 I 12 , 4 / '
^ C h o n C "
V i d u 19: Mach dien xoay chieu gom ba phan tu, dien tro thuan R, cuon cain
thuan L va tu dien C mac noi tiep Dien tro R thay doi dugc Dat vao hai
dau dogn mach dien ap xoay chieu u = 120 V2 coslOOjit ( V ) Dieu chinh R
khi R - Ri = 18 Q thi cong sua't tren mach la Pi, khi R = R2 = 8 Q thi cong sua*
P2, biet P I = P2 va Zc > Z L K h i R = Ih thi cong suat tieu thu tren mach dat cu^
dai Bieu thuc cudng do dong di^n qiia mach khi R = R 3 la
A i = 10 x/2 cos(1007tt + 7t/4) (A) B i = 10 72 cos(1007rt - 7r/4) (A)
C i = 10cos(1007tt + 7i/4) (A) D i = 10cos(1007rt-7i/4)(A)
R, R = 1 ^ tafi' cp, tart(p2 = 1 => (pi + <P2 = - •• ,
2) Ddo Iqi: NeU cp, + (P2 = ^ tin _Pi = Pz = P = ^^^^ ^ h i,n Q £e yv •
V i d u 20: Cho mach dien c6 2 pfian tit mSc noi tiep Va tu C va bieri tro R Do lech pha giua dien ap hai dau doan mach va dong dien qua mach u n g vcVi
cac gia tri Ri = 270 Q va R2 = 480 Q cua R la cpi va (p2 Biet (pi + 92 = n/2 Dien
ap hieu d u n g giua hai dau doan mach la 150 V Goi Pi va P2 la cong suat cua
mach ung voi Ri va R2 Tinh Pi va P2 OsJ^E - J' .^1 \ ,!f\ :4asf> • i •;'
Chu 1/; Dcfio sthili cong snii't ton nhict ta c6 ori' -Jirttlov -gn''"
thcdhng do thi P thco R Dm vao do tlii ta I >H nsn vf'b muhmln
R cdng gifn Rn thi cong sunt cdng Ian, cdng
xa Ro thi cong i^uat cdng be
P, = P2 = P thi Ro = |Z|, - Z,-\ V R J R ,
R 3 G ( R , ; R 2 ) = > P 3 > r ^ R3 ^ [ R , ; R 2 ] : : : ^ 1 ^ < P
Trang 12Bd trp kiSn thitc V^t It LTDH tren hSnh VTV2, t^p 2 - Chu VSn Blen
V i d u 2 1 : M o t mach dien xoay chieu g o m tu dien C, m o t cuon cam thuan L vo
m o t bien t r o R d u g c mSc noi tiep K h i R thay d o i t h i cong suat loa nhiet cuc
d?ii la P i r a x K h i de bien t r o a gia tri Ian l u g t la 18 Q, 32 Q va 20 Q thi con^
suat tieu t h u tren doan mach Ian l u g t la Pi, P2 va P:^ Ne'u Pi = P2 = P t h i
A P 3 > P B P 3 = Pinnx C Ps < P D P 3 = P
Huang dan
V i R3 e ( R , ; R 2 ) = > P 3 >P = > C h o n A • ,
ChtUj: • • •
1) Dc so sdnh vci P4 ta co thP'dung plurang pluip "giang day" nine sau: Tir P3 kc
dirang soug song vai true hoanh ncu P4 tren day tin P4 > P.) va nc'ii duvi day tin
P4 < Pi
1 ) Dc tun cong suat Ion nbat trong socac cong suat da cho, ta chi can so sank hai gia
tri gan dinh nhat bang pliuvng pluip "ginng day"
V i d u 22: M o t mach di?n xoay chieu g o m tu dien C, m o t cugn cam t h u a n L va
m o t bien t r a R d u g c mac noi tiep K h i R Ian l u g t bang 18 Q, 20 Q, 22 Q, 26,5
Q, 27 Q, va 32 Q thi cong suat tieu thu tren doan mach Ian l u g t la Pi, P2, ? \
P4, Ps va Vh Neu Pi = P(> thi trong cac gia trj cong suat noi tren gia trj Ion
^,, nhat la
A.P4 , •^T\n'^
V i t r i d i n h : /?„ = = 2 4 ( Q )
V i R cang gan Ro thi P cang Ion nen
chi can so sanh cong suat l i n g v o l R3
va R4 nam gan Ro nhat va hai phia
do'i v o i Ro
De so sanh P3 va P4 ta dung phuang
p h a p " g i a n g day", t u P 3 ke duong
song song v a i true hoanh va nhan
thay P4 nam d u o i day nen P4 < P3
Trang 13Bo trp kie'n thiic Vat li L roll trcn hcnii VTV2^Lpp^ 2- Chu Van Btett
V i d u 23: M o t mach xoay chieu mac noi tiep gom bien tro R, cuon day c6 do tir
cam L CO dien t r d thuan r va tu dien c6 dien d u n g C Dieu chinh bien tro de
R = r thi d u n g luc cong sua't tieu thu ciia mach cue dai Ti so'giua dien ap
hieu dung tren doan mach cuon day-tu dien va dien ap hieu d u n g tren toan
mach luc nay la • v , !
V i d u 2 4 : Cho mach dien xoay chieu RLC voi R la bie'n tro va cuon day c6 dien
trcV thuan r = 1 0 Q K h i R = 1 5 Q hoac R = 3 9 (.1 cong sua't cua toan mach la
n h u nhau De cong sua't toan mach cue dai thi R bang
V i d u 25: Cho mach dien noi tiep gom tu dien, cuon day c6 dien tra 10Q va
bien tro R Do lech pha giua dien ap hai dau doan mach va dong dien qua
mach Ling voi cac gia trj R: = 260Q va R2 = 470Q cua R la cpi va (p2 j
Bie't (pi + (p2 = K/2 Cho dien ap hieu dung giua hai dau doan m.ach la 150V
Goi P I va P2 la cong sua't cua mach uiig voi Ri va R2 Tinh Pi va P2
Khi thay doi R thi cong sua't toa nhiet tren toan mach dat gia tri cue dai la
A 1000 (W) B 144(W) C 800 (W) D 125 (W)
Huong dan '
(R + r ) 2 + ( z , - Z c ) ' , , / Ne'u ap d u n g P,„^^.^ <=> R + r = |ZL - Z^l => R = -20 < 0 : khong thoa man
1 0 ? : ( 0 + r) 200^ 40
Vi du 27: M o t doan mach mac noi tiep gom cuon day c6 dien tro thuan 40 (Q),
do t u cam L = 0,7/7t (H), tu dien c6 dien dung 0,l/7i (mF) va mot bien tro R
Dien ap 0 hai dau doan mach on dinh 120 V - 50 H z K h i R = Ro thi cong sua't
toa nhiet tren bien tra dat gia trj cue dai la Pm Gia tri Ro va Pm Ian lugt la
^flc/z nha nhanh: Cong sua't trcn bicn tra cue dai khi bien tra = tong tra plian con lai:
^ ' ^ - - = 2 ( R o + R , „ „ ) ^^.v
^* d u 28: Cho doan mach xoay chieu noi tiep gom bien tra R, cuon day c6 dien
tro thuan 30 Q c6 cam khang 50 7 3 Q va tu dien c6 d u n g khang 20 N/3 fi
, i • 145
Trang 14Bo tr^ hien thiic V^t li LTBtl tren kenh VTV2 t^p 2 - Chu Van Btin
Dieu chinh R de cong suat tren R c6 gia Ian nha't thi h§ so cong suat cijg
toan mach khi do la
V i 29: Cho mach dien RLC mac noi tiep, L c6 dien tra thuan r, con R la bien
tro Dat vao hai dau doan mach dien ap xoay chieu on dinh Dieu chinh Ian
lu(?t bien tra R c6 gia tri Ri = 50 Q va R2 = 10 Q thi Ian lugt cong suat tieu thu
tren bien tro cue dai va tren doan mach cue dai Tinh r
Binh luan: Sau khi tint ditgc r va | Z L
dai tren R, toan mach va tren r:
V i du 30: Cho mach dien RLC mac noi tiep, L c6 dien tra thuan r = 30 Q, con R la
bien tra Dat vao hai dau doan mach dien ap xoay chieu on dinh Dieu chinh
Ian lugt bien tro R c6 gia tri Ri va R2 thi Ian lugt cong suat tieu thu tren bien trO
cue dai PRmax va tren doan mach cue dai Pmnx Neu PRnux/Pmnx = 0,5 va R2 = 20 ^
Cty Train MTV own Khang VIft
V i du 31: Cho doan mach AB mac noi tiep gom tu di§n, cuon cam va bien tra
R Dien ap xoay chieu gifra hai dau doan mach luon on dinh Khi R = 76 Q thi cong suat tieu thu tren bien tra c6 gia tri Ian nha't va bang Po K h i R = R2 cong suat tieu thu cua mach AB c6 gia trj Ion nha't va bang 2Po Gia t n ciia R2 bang
R, + r 76+ r
tu dien CO dung khang Zc = 60 Q Dieu chinh R de cong suat tren R Ion nha't
Khi do dien ap giua hai dau doan mach chua cuon day va tu dien la 150 V
T i n h U
A 150 V B.261V C.277V D lOOV
COS(p :
Trang 15t o ' t r f i k l e n thu'c V $ t l l L T D I t t t e n k e n h VTV2, t^p 2 - C l i u V^n B i e n
tan(p,Lc =
Huotig dan
COS(p = ^ U = 2UR COS (p = 2.150COS — ~ 277 ( V ) ==> Choii C
; R thai/ doi lien qiian den cur tri I, UK, UL, UC, URI, URC, UI.C CI j.ct
' I, U L , Uc luon nghich bien theo R 1,11^,11^
* URI luon nghich bien theo R khi Zc < 2ZL
va luon dong bien khi Zc > 2ZL
URC luon nghich bien theo R khi Z L < 2Zc
va luon dong bien khi Z L > 2Zc
* Cac truong hgp de thi hay khai thac
Up = IR = = UVR <=> Ze = Z , 0««c/i cpn^ hu&ng!)
Vi du 1: Mach dien xoay chieu RLC mac no! tiep, co Zi = 100Q, Zc = 200^2, R In
bien tro (0 < R < x) Biet dien ap giua hai dau doan mach co bieu thiVc
u = 100 72 coslOOTit (V) Dieu chinh R de Ui,,„.x khi do
-Vi du 2: (DH-20I0) Dat dien ap xoay chieu co gia trj hieu d u n g 200 V va tan so
khong doi vao hai dau A va B cua doan mach mac noi tiep theo thiV tir gom bien tro R, cuon cam thuan co do tu cam L va tii dien co dien dung C thay doi Goi N la diem noi giua cuon cam thuan va tu dien Cac gia trj R, L, C hCfu han va khac khong Voi C = Ci thi dien ap hieu d u n g giua hai dau bien tro R CO gia trj khong ctoi va khac khong khi thay doi gia tri R cua bien tro Voi C = 0,5Ci thi dien ap hieu dung giua A va N bang
Vi du 3: (DH-2010) Dat dien ap u = U V2 coscot vao hai dau doan mach AB gom
hai doan mach A N va NB mac noi tiep Doan A N gom bien tro R mac noi tiep voi cuon cam thuan co do tir cam L, doan NB chi co tu dien vtii dien dung C Dat coi = 0,5(LC)^'^ De dien ap higu dung giua hai dau doan mach
A N khong phu thuoc R tiii tan so goc co bang
A 0,5o)i/V2 B (01V2 \ W1/V2 D 2(01
149