CAp TOC BAI TAP VAT LY luyen thi Dai Hoc THPTQG

pHAM DLfC CLfdNG (Chu bien)
E TAN Rl - BUI IRAN DLfC ANH THAI,
THAN THANH SANG

530.076
L527TH

CAC DANG BAI TAP TQ CAC D E THI QUOC GIA

(TOT NGHIE P - T U Y E N kINH)

VAT^Y
/

^

C a c de c h i n h thiic v a de l u y ^ n t a p
p a n va thang diem ciia B Q Giao due va Dao

tao

(Tai b a n , svfa chvTa v a bo sung)
Cho mach dien xoay chieu nhif h i n h ve. Bi^t cuon day c6 dien t r d khong
~ dang ke. K h i khoa k dong dong dien qua mach cham pha hofn dien ap hai
_ d^u mach la —. K h i khoa k md dong dien qua mach nhanh pha
.i....:4„:..,,_4_.i.
horn dien ap hai dau mach la —.
4
Moi lien he giOfa cam
dung khang Zc cua ma
-|i4

A. Z L = (V3 + DZc
D V L 0 1
C. Z:. =

^

D.

ZL =

M

1 1 7 0

(73-

DZC

NHA XUAT BAN DAI HOC Si/ PHAM


PHAM DLfC CLfdNG (Chu bien)
LE TAN Ri - BUr TRAN DISC ANH THAI - THAN THANH SANG

LUYEN THI CAP TOC
•

CAC DANG BAI TAP TlT CAC OE THI QUOC GIA

(^at nqklift - ^tufln dnh)

VAT L Y
Cac de chinh thCfc va de luyen tap
Dap an va thang diem cua Bg Giao due va Dao tqo
(Tdi ban, sura chufa va bd sung)
THt; V i a ; TNVH BiNH VHUAW

NHA XUAT BAN DAI HQC Si/ PHAM


www.matheducare.com
MUC L U C
Phan 1: Tom tat giao khoa

49
53
53
54
56

B. Phan rieng cho chirong trinh nang cao
Dpng lyre HQC vat ran
Con lac v§t K
Hi?u img Dop-ple
Thuyet tuong doi h^p
Thuyet Big bang

3
6
13

17
25
31
37
43

A. Phan chung cho cce ban va nang cao
Dao dpng ca
Song ca
Dao dpng di^n tir - song difn tir
Dong di?n xoay chieu
Song anh sang
Lugng tir anh sang
H^t nhan nguyen tir
Tir vi mo den vT mo

Phan 2: Kien thirc can nhor

77
80
80
80
82

B. Phan rieng cho chirong trinh nang cao
Ca hpc v^t ran
Con lac v§t li
Hi?u irng Dop-ple
Quang di$n
Tia X (Ronghen)

58
64
66
69
70
73
74

A. Phan chung cho co ban va nang cao
Dao dpng CO
Song ca
Dong di?n xoay chieu
Dao dpng di^n tu
Song anh sang
Quang di^n
Vat li h^t nhan

Phan 3: Dap an va huoTig dan giai cac de on luyfn Tu Tai
Phan 4: Dap an va hv&ng dan giai cac de on luyf n Dai h9c - Cao dang

83
190


^han t:
Phan

TdM T A T G I A O K H O A
chujif cho ban of ban ad ndn^ eao

DAO DONG CQ

I. Dao d9ng dien hoa :
* Dao dpng tuan hoan la dao dpng ma trang thai chuyen dpng cua vat dupe l$p
lai nhu cij sau nhung khoang thai gian bSng nhau.
* Chu ky la khoang thai gian ngan nhat de tr^ng thai dao dpng cua v^t l^p l^i
nhu cu hay thai gian thvrc hi?n 1 dao dpng toan phan.
* Dao dpng dieu hoa la dao dpng dupe mo ta bang djnh lu^t dang cos hoae sin:
X = Acos(cot+ (p)
Vai:
+

X la li dp ciia dao dpng (khoang each dgi sS tir vat den v/ tri can bdng)

+ A la bien dp cua dao dpng, don vj : m; em (A =
+

/x„a.x/)

CO la tan so goc ciia dao dpng, don vj : rad/s (co cho biit dao dpng nhanh
hay chants co Id toe dp bien doi ciia goc phaj

+ (cot + cp) la pha dao dpng t^i thai diem t, pha chinh la doi s6 cua ham
cosin va la mpt goc. (Pha dao d0ng cho ta biet v/ tri vat dao d^ng, gid tri
vd each bien thien cua vgn toe va gia toe vat dao dgng. Pha dao dgng xde
dfnh trgng thai vat dao dqng).
+ (p la pha ban dau ciia dao dpng (Pha ban ddu xde dinh trgng thai ban ddu
ciia vgt dao d(>ng, ph^i thuQc each chgn goc tog dp vd goc thai gian).
+ Vgn toe va gia toe v|it dao dpng dieu hoa bien thien cung tan so vai tan so
v^t dao dpng.

+ V$n toe nhanh pha ^ so vai li dp x
+ Gia toe ngupc pha so vai li dp x
* Lye tac diing lam vat dao dQng dieu hoa:
+ C6d9ngF = - k x
+ Lvrc nay luon huang ve VTCB nen dupe gpi la \\fc keo ve (hay lye hoi
phye).
* Dao dpng eiia con lac 16 xo la mpt dao dpng dieu hoa co chu ky:

3


* Voi goc l^ch nho, dao dgng ciia con lac don la mpt dao dgng dieu hoa c6 chu ky:

T= 2 n Vg
* H f dao dQDg:

+

thvrc hi^n dao dpng t\ do dupe gpi la hf dao dpng.

+ Dao dpng t\ do la dao dpng xay ra duoi tac d\ing ciia npi l\rc (Noi each
khdc dao dgng tir do c6 chu ky chi phu thuQC cac dgc tinh ciia h^, khong
phu thuQC cdc yeu to ben ngoai).
+ Chu ky cua dao dpng t\ do con gpi la chu ky rieng.
Vidu:
+ Con lac Id xo la rnqt h^ dao dgng (c6 chu ki chiphy thuQC vao m va
k), l\cc dan hoi tac dung vac vgt la ngi l\rc.
+ Con lac dcm va Trdi ddt (hay con lac vgt It vd Trdi ddt) Id h? dao
n. Cor nSng:
Do v^t n^ng trong con iSc 16 xo chju tac dyng ciia l\rc dan hoi va trong con iSc

don la trpng lyc nen ca nang ciia v$t dupe bao toan vi l^rc dan hoi va trpng Ivrc
la nhung \\fc the.
* Co' nang trong dao d$ng dieu hoa:
+ The nang: E, = ^ kx^ = ^ kA^cos^(cot + cp)
+ Dpng nang: Ea = ^ mv^ = ^ kA^sin^((ot + 9)
+ Ca nSng toan phan: E = E, + E^ = — kA^ =—mco^

= const

V$y trong suot qua trinh dao dpng dieu hoa c6 s\f chuyen hoa nSng lupng gi&a
the nSng va dpng nSng nhung ca nSng khong doi va ti I9 vai binh phuang bien
dp dao dpng.
III. Dao dgng t^t dan:
Dao dpng tat dan la dao dpng c6 bien dp giam dan theo thai gian do tac dyng
ctia ma sat nhot.
* D^c diem:
+ Dao dpng tat dan noi chung khong c6 tinh dieu h6a nhung khi xet trong thai
gian ngin ta c6 the coi la dao dpng dieu hoa vai chu ki rieng va tan so rieng.
+ L\rc can moi truang cang Ian (hay moi triwng cdng nhot) dao dpng tat dan
cang nhanh.
+ Dp nhot cua moi truong tang theo thu t\r: khong khi, nuac, dau, dau rat nhot.
4


T

I V . Dao d^ng duy tri:
Dao dpng dupe cung cap nSng lupng de bu l^i phan nSng lupng mat di do ma
sat ma khong lam thay d6i chu ki rieng cua no gpi la dao dpng duy tri.
* Dao dpng duy tri eo ngo^i l^rc tac dyng, ngo^i l^rc nay dupe dieu khiSn

+ de C O t i n so goe bSng tan so goc dao dpng t\ do cua h?.
+ boi chinh dao dpng ky qua mpt ca cau nao do.
* Tan so va bien dp dao dpng duy tri v i n bSng nhu khi h$ dao dpng t\ do.
V. Dao d^ng cir&ng birc:
la dao dpng dupe duy tri do tac dyng cua mpt ngo^ii l^rc bien doi dieu hoa:
F = FoCosQt
+ Dao dpng cu&ng buc la dao dpng dieu hoa.
+ Tan so dao dpng eixong buc bSng tan so ngo^i Ivrc.
+ Bien dp dao dpng cuong buc ti I9 vai bien dp Fo cua ngo^i lyre va phy thupc
tan so cuong buc D. cua ngoai l\rc ( AQQ e | Q - CO| ) .
VI. S y C9ng hirong:
+ Hi?n tupng bien dp dao dpng cu&ng buc tang nhanh den mpt gia trj eye d^i
khi tan so f cua lyc cir&ng buc bang tan so rieng cua v^t dao d9ng gpi
la hi$n tupng cpng huong.
+ Bien dp dao dpng d^t den gia trj khong doi va eye

khi toe dp tieu hao

nSng lupng do ma sat bSng toe dp cung cap nSng lupng cho h^.
+ Bien dp eye d^i ciia dao dpng khi cpng huong phy thupc ma sat moi truong:
ma sat giam thi gia trj eye d^i bien dp ting.
* Phan bi?t dao dpng cv&ng birc vol dao d9ng duy tri:
+ Dao dpng cu&ng buc la dao dpng xay ra dudi tac dyng ciia ngo^i lyc tuan
hoan C O tan s6 goc Q bat ki. Khi on djnh dao dpng cuong buc c6 tan so biing
tan so ngo^i lyc.
+ Dao dpng duy tri cung xay ra dudi tac dyng ngo^i lyc nhung ngo^i lyc dupe
dieu khien (boi ehinh dao dpng ay) de c6 tan so goc bang tan so goc ciia dao
dpng ty do ciia h?.
VII. Tong h(fp dao d^ng:
*

Xet hai dao dpng dieu hoa cung phuong, cung ikn so:
X ] = Aicos(cot + cpi);
X2 = A2cos(cot + 92)
Tong hpp hai dao dpng dieu hoa cung phuong, cung t i n so la mpt dao dpng
dieu hoa cung phucmg, cung tan so voi hai dao dpng thanh phan.
+ Bien dp hai dao dpng tong hpp: A =

^Aj

+ Aj

+ Pha ban dau hai dao dpng tong hpp la 9, voi:
t a i K p ^ Aisincpi + A^sincp;
AiCOSCpi + A2C0S(P2

+2AiA2COs(92


+ Neu hai dao dOng thanh phan cung pha: 92 - (Pi = 2kn
=>

A = A , + A2 ; (() = (pi = 92

+ Neu hai dao dgng thanh phan ngirgrc pha: 92 - (Pi = (2k + 1 )7t
A =

Noi chung :

A | - A2 ; cp = (pi

neu

Ai >

Aj

A, - A 2 < A < A , + A 2

SONG c a
I. Song ca:
+ Song CO hpc la nhCrng dao dpng co Ian truyen trong mOt moi truong.
+ Song CO du(?c t ^ thanh nha lyc lien ket dan hoi giira cac phan tir ciia moi tmong
truyen dao dpng di. Cac phan tir cang a xa tam dao dpng cang tre pha hon.
+ Khi song truyen chi c6 trang thai dao dpng (pha dao dgng) truyen di con ban
than cac phan tOr vat chat chi dao dpng t^i cho.
* Song ngang:
+ Co phuong dao dpng vuong goc vai phuong truyen song.
+ Truyen trong moi truong c6 l^rc dan hoi xuat hi?n khi bj bien dang l?ch (Vd:
Song truyen tren mat nuac, spi day dan hoi, tam kim lo^i mong..).
+ Song tren m§t chat long la do hpp lyc c5ng mat ngoai va trpng lyc c6 tac
dyng giong nhu lyc dan hoi.
* Song d9c:
+ Co phuong dao dpng trung vai phuong truyen song.
+ Truyen trong moi truong c6 lyc dan hoi xuat hi^n khi bj bien dang nen, dan
(Vd: Song truyen tren 16 xo khi 16 xo nen va dan...)

II. Cac dai lirQiig dac trirng ciia song :
* Chu ky, tan so ciia song: la chu ky, tan so dao dpng chung ciia cac phan tii
v^t chat CO song truyen qua va bang chu ky, tan so ciia nguon song =:> Chu ki

va tan so khong doi khi song truyen.
* Toe d9 truyen song: la toe dp truyen pha dao dpng. Trongrnqtmoi tru&ng
toe dQ truyen song khong doi)
* Buoc song X: Buac song la khoang each giua hai diem gan nhau nhat tren
Cling mpt phuang truyen song va dao dpng ciing pha voi nhau. Buoc song
cung la quang duong ma song truyen dupe trong mpt chu ky song.
X = vT = ^
f
6


*

Bien d9 song: Bien dp song t^ii mpt diem la bien dp dao dpng cua phan t i i
vat chat tai diem do khi c6 song truyen qua.

*

Nang

liTQTig

cua song: Qua trinh truyen song la qua trinh truyen nang

lugng. Nang lugng song tai moi diem t i I9 v a i binh phuomg bien dp song tai
diem do. M p t phan tir v$t chat dang dumg yen khi c6 song truyen den se dao
dpng, nghia la phan tur do da nh$n dupe nang lugng tir song. Vay qua trinh
truyen song cung la qua trinh truyen nang lupng.
I I I . PhiroTig t r i n h song :
Xet song truyen tir nguon O den diem M each O mpt doan O M = x.

Gia sOr phuorng trinh dao dpng t ^ i nguon O la : UQ = Acoscot
Song truyen tir O den M mat thai gian to = —
Phuong trinh dao dpng tai M each O doan d la:
Uyj =

UMCO

= Uo(t

- to)

Acos(©t-^)

hay U M = A c o s c o t - Y ' ' ) (*)
( • ) cho ta xac djnh l i dp ciia phan tur song t ^ i diem M bat k i tren ducmg truyen
song, gpi la la phuong trinh song.
*

Neu song truyen nguQc chieu vai chieu dircmg true Ox thi phmxng trinh
song CO dgng:

= A c o s ( — t + — x)

Tir (*) ta thay song c6 hai tinh chat:
+

Tinh tuan hoan theo thoi gian:
K h i xet mpt diem P tren song c6 toa dp x = d.

Ta thay l i dp u cua P bien thien theo ham cos => chuyen dpng cua diem P la

mpt dao dpng tuan hoan vai chu k i T = — .
(0

+

Tinh tuan hoan theo khong gian:
K h i xet tat ca cac diem tren song vao thai diem to,
(*)

" M = Acos( Y

to - Y

x)

Ta thay l i dp u cua cac diem tren song bien thien tuan hoan theo l i dp x =>
hinh dang song (hinh sin) tai thai diem to : cu sau mpt buac song thi song lai
C O hinh dang nhu truac.
7


D^c bift:
+ NhiJng diem tren phuong truyen song dao dgng cung pha v a i nguon k h i
— x = 2k7i=> x = kX v a i Ikl

=0,1,2,...

+ N h u n g diem tren phuang truyen song dao dpng ngugc pha v a i nguon khi
— x = ( 2 k + 1)71=^ x = (k + - ) X

A.

2

I V . P h a n x a song:
Song dang truyen trong mpt moi truong ma g^p v§t can thi bj phan x^. Song
phan X 9 c6 ciing tan so va buac song ciia song t a i .

Neu v^t can tyr do thi song phan x? luon luon ciing pha v a i song t a i a d i l m
phan x^.

+

Neu v$t can c6 djnh thi song phan x^ luon luon ngugc pha v a i song tai a
diem phan x^.

+

V . Song d i r n g :
Song dCmg la song c6 nhCrng diem dung yen (nut song) va nhOng diem dao
dgng v a i bien dp c^rc d^i (byng song) trong khong gian.
Dac d i l m :
V j tri cac nut va cac byng la c6 djnh.

+

Song diing la svr giao thoa giua song t a i va song phan x^ tren cdng phuang.

+

V j t r i cac byng luon each dau c6 djnh nhung khoang bSng mpt so le l4n
mpt phan t u buac song.

-

V j t r i cac nut luon each d i u c6 djnh nhirng khoang bSng mpt so nguyen
Ian nua buac song.

-

3l

+ Khoang each giua hai nut (ho$c hai byng) ke nhau dfiu bSng —.
Dieu kif n c6 song dirng:
-

K h i hai dau day c6 djnh: De c6 song dung, chieu dai spi day b^ng so
nguyen \kn nua buac song
^ = k | (vai k = 1,2, 3
;
=> tren day c6 so byng bang so bo bang k, con so nut lak+

-

1.

K h i mpt dau day t y do va mpt dau day c6 djnh: De c6 song dung, chieu
dai spi day bang so nguyen le Ian mpt phan t u buac song
l = m—
4

(vai m = 1, 3, 5....)

=> tren day c6 so bung bang so nut bangn = ~~~

-^on so bo Ian

-1

ifng dyng cua song dirng: Do v$n toe truyen song.
8


VI. Giao thoa song:
* Hai nguon dao dpng cung tin s6 va c6 dp i?ch pha khong doi gpi la hai
ngu6n ket hgrp. Song ma chiing t^o ra dugc gpi la song ket hgrp.
* Giao thoa la s\c t6ng hgp cua hai song ket hgrp trong khong gian, trong do c6
nhixng cho c6 djnh ma bien dp song dugc tang cucmg ho^c bj giam bat.
* Dieu kif n c6 giao thoa: Hai song la hai song ket hgrp va dao dpng cung phuong.
* Ly thuyet ve giao thoa:
Gia sir A va B la hai ngu6n ket hgrp c6 cung phuorng trinh dao dpng la:
U A = U B = Acoscot
Xet diSm M bat ky trong moi truong each A mpt doan di va each B mpt doan d2.
Phuorng trinh dao dpng t^i M do song tCr A den: ui = Acos(cot -

)

Phuorng trinh dao dpng t^i M do song tir B den: U 2 = Acos(cot -

)

K

Dao dpng t^i M la tong hpp cua hai dao dpng tren.
2nd,,
,
,
- ) + Acos(cot

u = u, + U2 = Acos(cot
o

7t(d2-d,)

u = 2Acos—^^^^

*^cos c o t -

7t(d2

2nd,,
-)

+d,)

V$y dao dpng t^i M la dao dpng dieu hoa voi bien dp :
A ^2 A cosTa thay A phy thupc vj tri cua diem M
Nhir vay:
* T^ii M CO bien dp c\rc d^i

- 2A (hai dao dpng thanh phdn ciingpha :

= 2kK) khi : cos 7 t ( d 2 - d i ) = 1 o
Vay: Tai nhirng diem M c6
hi^u dircmg di b§ng so
nguyen Ian birffc song thi
bien
dao d9ng tong h9rp
c^c dai va hpp thanh mpt hp
cac duong hyperbol nh?in A
va B lam tieu diem (ke ca
duong trung tr\rc cua AB).

dj - d, = kA, voi k = 0, ±1, ±2,...
k = l

k =0

k = -l
k = -2

k =2

k'=-2

k-=o

k'=-l


* Tai M CO bien dp c\rc tieu

A(p = (2k + l)7t) khi : cos
d2 - d , = (k +

= 0 (hai dao dgng thanh phan ngu^c pha :
7t(d2-d,)

=0

vai k = 0, ±1, ±2,...

Vay: Tai nhirng diem M c6 hi|u ducmg di bing mpt so ban nguyen Ian
birofc song thi bien dp dao dpng tong hpp cue tieu va hpp thanh mpt hp
cac dircmg hyperbol nh^n A va B lam tieu diem.
Chuy: DQ l^ch pha cua hai dao d(mg thanh phan la:
27r(d2-di) 2nd
A© =
=
X
X
Dung dg l^ch pha ta cung c6 the tim ra ditQC cac kit qua nhu tren
* Y nghia cua hif n tuyng giao thoa song: Khi c6 hi^n tugng giao thoa xay ra
thi CO the ket lu^n doi tugng dang nghien cuu c6 ban chat song.
V I L Nhieu xa song:
+ La hi^n tupng song khi gap vat can se di l^ch khoi phuong truyen thang cua
song va di vong qua vat can do.
+ Hi?n tupng nhieu
thoa song.

la mpt d§c tinh c6 hiru cua song, giong hi?n tupng giao

V I I I . Song am:
Khi mgt vgt dao dgng se lam khong khi a ben bj nen roi bi dan, xudt hi^n luc
dan hoi trong khong khi vd lam dao dgng nay truyen din cac phan tir khi a xa
horn. Dao dgng truyen di trong khong khi tgo thanh song dm.
Nhu v$y:
+ Song am la nhung dao dpng phat ra tir nguon am, dupe truyen qua khong khi
vao tai ta lam mang nhT dao dpng gay ra cam giac am.
+ Song am la nhung song co truyen trong moi truong vat chat (khi, long, An).
- Trong chat khi vd chat long song dm la song dgc vi trong cac chdt nay
l\K dan hoi chi xudt hi^n khi co bien dgng nen, dan.

Song ha am la nhirng song co hpc co tan s6 f < 16 Hz

-

Song sieu am la nhirng song ca hpc co t^n s6 f > 20 000 Hz

-

Song am ma tai nguai CO the cam thy dupe CO tan so tir 16 den
Hz, con gpi la am thanh.

-

Trong chdt ran gom cd song ngang vd song dgc vi trong chdt rdn l\rc dan
hoi xudt hi^n khi c6 bien dgng l^ch hogc nen, dan.

-

20 000

+ Sy phan bift song am, ha am va sieu am la do s^r cam thy am cua tai con
nguai. Cac song nay co ban chat v^t li giong nhau va giong vai cac song ca
hpc khac.
10


*

Song am t r u y e n dugc trong tSt ca cac moi truong k h i , long, ran nhimg
khong truyen dugc trong chan khong.
+

Song am truyen di rat kem trong chat xop ; nhung ; bong ; val ....

+ Trong moi moi truong am dugc truyen d i v a i toe dg xac djnh.
* Toe d9 t r u y e n am phu t h u g c :

-

Tinh dan h6i va khdi lugng rieng cua moi truong.

-

Nhi$t dg ciia moi truong.

Noi C h u n g Vri„ > vi6„g > vwhi

Chiiy:

Trong chdt rdn song am c6 the Id song ngang hade song dqc.

* Nhac am: la nhung song am c6 tan so xac djnh (va thuang keo ddi), c6 do thj
dao dgng la nhung duong cong tuan hoan. Vidu : tieng hat, tieng

dan...

* T a p am: la nhung song am khong c6 tan so xac djnh, c6 do t h j dao dgng la
nhung duong cong khong tuan hoan. Vi du: tieng may no

IX: Cac dac trimg sinh ly cua nhac i m :
*

D9 cao cua am:
La mgt dac tinh sinh ly cua am, gSn lien v o i tan so am. Am cd tdn so l&n gpi
la dm cao hogc dm bong. Am c6 tdn so nhd gpi la dm thdp hodc trdm.
A m cang cao khi tan so cang Ion, nhung dg cao ciia am khong t i I9 vai t i n so.

*

A m sac :
Khi mQt ngudn dm phdt ra niQt dm cd tdn sof (dm ca ban) thi cUng dong thai
phdt ra cdc hga dm cd tdn so la bQi s6 ciia f. TUy theo cdu trite cua

ngudn

dm ma cdc hpa dm c6 so li/tpig. bien dp, thai gian ton tgi khdc nhau.
Am phdt ra la tong hQp ciia dm ca ban vd cdc hga dm, no cd tdn sd

fnhwig

duong bieu dien cua nd khdng con la duong sin md tra thdnh mgt

duong

tudn hoan phirc tap cd chu ki. Moi dgng cua duong bieu dien img vdi niQt
dm sdc nhdt djnh. Do dd cdc ngudn dm khdc nhau se tgo ra nhirng dm sac
khdc nhau.
Vay:
+

A m sac la mgt d$c tinh sinh l i ciia am giup ta phan bi?t dugc cac am cung dg
cao nhung phat ra t u nhiJng nguon khac nhau.

+
+

A m sic dugc hinh thanh dyra tren tan so va bien dg am.
A m sac gan lien v a i d6 thi dao dgng am. A m sac khac nhau k h i dang do thj
dao dgng am khac nhau.

+

Cdc nhac cu khdc nhau khi phdt ra dm cd cimg dp cao se cd dgng do thj dao
dgng dm vdi tdn so giong nhau nhung cd li dd bien ddi khdc nhau => dd thi
dao dgng dm khdc nhau.

*

Dg to cua am:

Nang lu-gng am: Nang lugng am t i 1^ v o i binh phuong bien dg song am.
11


Cirong d9 am I : la nSng lugng ma song am truyen trong mpt don vj thai
gian qua mpt don vj difn tich d$t vuong goc vai phuong truyen am.
S
+ Dan vj cua cuong dp am I la W/m^.
+ Cirang dp am la mpt d$c tinh vat li cua am.
Mire cirong dp am L :

i

+ Am thanh nghe cang to khi cuong dp am cang Ian.
+ Dp to cua am khong ti 1? vai cuong dp am.
+ Cam giac am tang theo loga ciia cuong dp am.
+ De so sanh cuong dp ciia mpt am voi cuong dp am tieu chuan nguai ta
dung muc cuong dp am L :
L = 10lgi(I la cif&ng

dm gay ra a tai nguai; I„ la cirang

dm tieu chudn)

+ Don vj mure cuong dp am la Ben (B) hay dexiben (dB)
+ Muc cuong dp am la mpt d§c tinh v^t li ciia am.
Chuy:

Am md tai nguai nghe duQC c6 cuong dQ nhd nhdt Id lo Oo gQi Id ctrnng
dQ dm chudn). Nguai ta chgn k = 10 ''^ W/m^ Id cuong dp dm chudn cua

dm.

-

Tai nguai phdn bi?t dugc hai dm c6 mice cuong dQ chenh l^ch nhau it
nhdt la I dB.

-

- Am md tai ngitai nghe duQfc c6 ctrong dQ Ion nhdt bdng 10 W/m^.
-

Muc cuong dQ dm tieu chudn bdng 0 vd muc cuong dQ dm manh nhdt
bdng 130 dB (L„ax = lOlg-^

I.

= 130 dB)

D9 to cua am : la mpt d^c tinh sinh ly cua am, ph\ thupc cuong dp am va
tan so am. Dp to cua dm gdn lien v&i muc circmg dp am.

\

* Nguon nh^c am : Co hai lo^ii nguon nh^c am chinh :
+ Day dan hai dau c6 djnh:
-

Tren day dan se c6 song dung khi chieu dai day la:
^ = k | ( v o i k = l,2,3...)hay ^ - k ^ .

-

Nhu v^y voi day dan c6 chieu dai £ va c6 dp cang day khong d6i thi
^

'

V

song dung xay ra khi tan so f = k —
12


T

-

Khi kich thich cho day dan dao dgng thl tren day c6 song dCmg va phat ra
am CO ban (hay ho^ am b^c 1) umg vai k = 1, ciing cac ho? am b^c 2 ; bac
3 ... ung vai k = 2 ; 3 .. Am tong hgrp la mpt dao dpng tukn hoan phuc t^p
CO cung tan so am ca ban (nen moi logi dan c6 dm sac khdc nhau).

+ 6ng sao (hay ken):
-

Cau t^o ong sao (hay ken) c6 bp ph^n chinh la mpt ong c6 mpt dSu kin,
mpt dau ha. Khi th6i mpt lu6ng khi vao ong thi khong khi trong ong dao
dpng va trong 6ng c6 song dung khi chieu dai ong thoa dieu ki^n :
l = m- ( v a i m = 1 , 3 , 5 ...)hay ^ - m — .

4
4f

-

Noi each khac vai ong c6 chieu dai £ thi song dung xay ra khi tan so
f=m-:^.

-

Khi thoi sao thi trong ong sao c6 song dimg va phat ra am ca ban (hay
ho9 am b^c 1) umg vai m = 1, cung cac ho? am b?c 3 ; b?c 5 . . . irng vai
m = 3 ; 5 .. Am tong hgrp la mpt dao dpng tuan hoan phurc t?p c6 cung tan
so am ca ban (nen moi logi sao hogc ken c6 dm sac khdc nhau).

-

Chieu dai ong cang Ian thi tan so f cua am phat ra cang nho.

* Hpp C9ng hirong : la mpt v^t rong c6 kha nang cpng huang vai nhieu tan so
am khac nhau d l tSng cuang nhung am do.

DAO DONG OIEN TU'
SONG DIEN TLF
I. M^ch dao d9ng:
La mpt m?ch kin gom mpt ty difn c6 di^n dung C m4c noi tiep vai mpt cupn
cam L (difn tra ho?t dpng R = 0). M?ch dao dpng ho?t dpng d\ra tren hi?n
tupng t\ cam.
I I . Syr bien thien cua di^n tich trong m^ch dao dQng :
Di^n tich cua t\ dif n trong m?ch dao dpng bien thien dieu hoa vai tan so goc

1
VLC •

+ Chuki dao dpng rieng: T = 27tVLC
+ Phuang trinh dao dpng cua di^n tich : q = Qo cos(cot + (p)
+ Cuang dp dong di^n trong m^ch:
i = q' = -coQo sin(a)t + cp) = coQo cos((at +

)
13


+ Di?n ap giCra hai ban tu: u = — = — cos((ot + cp)

c

c

+ Di$n truong E trong ty di^n ti I9 thuan vai di^n tich q ciia
va cam irng tir
B trong cugn day ti I9 thu^n vai dong difn i qua cupn day => tir truong va
di?n tnrcmg trong m^ch dao dpng tuan hoan.
V^y: S\ bien thien tuan hoan theo quy lu^t ham sin ciia i, q va u (ho$c syr bien
thien tuan hoan theo quy lu^t ham sin ciia di?n truong va tir truong) trong m^ch
dao dpng dugc gpi la dao dpng tg do.

III. Dao dpng di^n tir trong mach dao dQng :
1

.

Nang lupng di?n truong t^p trung o ty di?n : WNang lupng tir truong t^p trung 6 cupn cam : Wt = — Li^ = — sin^(cot + 9)
Nang lupng cua mach dao dpng: W = Wd + Wt = — Cu^ + — Li^
2
2
2C

2

°

2 °

V9y:
+ Nang lupng cua m^ch dao dpng gom nang lupng difn truong a ty di^n va
n^ng lupng tir truong o cupn cam.
+ N i n g lugng di^n truong va nang lupng tir truong biln thien tuan hoan vai
cimg mpt tan so f (vai f =2 f ; f la tan so dao dpng cua di?n tich trong
m^ich).
+ N5ng lupng cua m^ch dao dpng dupe bao toan.
+ Dao dpng di^n tir cua m^ch dao dpng la mpt dao dpng ty do.

IV. Dao d9ng di^n tir tat dan:
Thyc te cac m^ch dao dpng deu c6 di?n tro R nen khi dao dpng trong mach se
toa nhift nen mach dao dpng tat dan.

V. Dao d^ng di^n tir duy tri - hf ty dao d^ng :
Muon dao dpng di?n tir khong tat dan nguai ta duy tri dao dpng bSng each cung
cap nang lupng cho m^ch de bii vao phan nang lupng da tieu hao bSng may

phat dao dpng dieu hoa dimg tranzito. Tan so cua dao dpng d i | n tir do may phat
ra bang tan so rieng cua m^ch L C : fn =

^ =
27tVLC

=:> m^ch nay gpi la h? t\ dao dpng.
14


VI. Dao dQng dif n tir circrag bu-c - Sir CQng hirong:
+ MJc mach dao dpng LC c6 tin s6 dao dpng rieng la fo vai mpt nguon di$n
ngoai CO di?n ap bien thien dieu hoa: u = Uocos27ift => dong di^n trong mach
se bien thien theo tan so f cua di?n ap u chu khong bien thien theo tan so fo
nOa. Luc nay dao dpng^ong m^ch la dao dpng cuong buc.
+ Khi tan so f = fo thi bien dp dao dpng di?n trong m^ch d^t gia trj c\rc dai =>
trong m^ch c6 cpng huong dif n. Vai di?n tra R cua m^ch cang nho thi bien
dp khi cpng huong rat Ian.
+ Hifn tupng cpng huong di$n dugc umg dyng trong mach Ipc; mach chpn
song ; m^ch khuech d^i

* Sir tirong tu- gifra dao dyng di?n tir va dao dyng co":
GiCra dao dpng di?n tu va dao dpng co c6 syr dong nhat ve hinh thuc (cac
phuang trinh va cong thuc c6 cung mpt dang) ma con la syr dong nhat ve quy
luat bien doi theo thai gian.

VII. Di^n tir trirong:
* Hai gia thuyet cua Macxoen (Maxwell):
+ Trong vung khong gian c6 tir truong bien thien theo thoi gian se xuat hifn
trong khong gian do mpt dif n truong xoay.

Dgc diem cua di^n truong xoay: Cac dic&ng sire la cac durang cong khep kin
baa quanh cac dmmg cam vmg tir. No khac han cac du&ng siec cua tru&ng
tinh di^n di ra tic di^n tich duang va di vao di^n tich dm.
+ Trong vung khong gian c6 di?n truong bien thien theo thai gian se xuat hi?n
trong khong gian do mpt tu truong.
Ban chat ciia tir truong la cac duomg cam img tir ludn xoay.

* Difn tir trucmg :
Theo Macxoen: Trong vung khong gian c6 tir truong bien thien theo thoi
gian se xuat hifn mpt difn trirong xoay, va c6 difn truong bien thien theo
thai gian thi xuat hif n mpt tir truong trong vung do.
+ Di?n truong hoac tu truong khong the ton tai dpc lap voi nhau. Dif n truong
va tir truong la hai mjt the hifn khac nhau cua mpt lo^i truong duy nhat gpi
la dif n tir truong.
+ Truong difn tu la mpt d^ng v^t chat, dong vai tro truyen tuong tac giOa cac
difn tich. Tuong tac difn tir Ian truyen trong khong gian voi v^n toe bang
v^n toe anh sang .
Di4n truong tinh va tir truong tinh la trirong h(/p rieng cua di?n tir truong.

VIII. Song di?n tir :
Song difn tir la qua trinh truyen di trong khong gian ciia mpt difn tir truong
bien thien tuan hoan theo thoi gian.

15


* Song dif n tir
+

CO v^n toe truyen song difn tir trong chan khong bang v$n toe anh sang

c»3.10Ws.

+ la song ngang. T^i mpt diem bat ky tren phuomg truyen, vecta cuong dp di?n
trirong E va vecto cam ung tir B vuong goc nhau va cung vuong goc vai
phuang truyen song. Dao dpng ciia di^n truang va cua tu truang luon cung
pha vai nhau.
XI
CO buac song trong chan khong la
(vai c la vgn toe dnh sang ;fla tan so cua song di^n tir).
+ truyen trong moi trirong v$t chat (cac difn moi), va ca tiong chan khong.
+ CO the cho cac hi^n tupng : phan x^, khiic xa, giao thoa ... va tuan theo cac
quy lu^t nay.
+ CO mang nang lugng. Nha c6 nSng lirpng ma khi song di?n tir truyen den
mpt anten, no se lam cho cac electron ty do trong anten dao dpng.
Nguon phat song di?n tir la nhijng nguon t^o ra di^n truang ho|ic tir truang bien
thien ban dau nhu : tia lira di?n, cau dao ngSt di^n ...
Nhung song di^n tu c6 buac song tir vai met den vai kilomet dupe diing trong
thong tin lien l^c v6 tuyen nen gpi la cac song v6 tuyen.
I X . Mach dao dQng hit - Angten :
Trong m?ich dao dpng kin: hau het di^n tu truang biSn thien t$p trung trong ty
difn va cupn cam. M^ch khong buc x^ song di?n tu.
Trong m^ch dao dpng ha: di$n tir truang vupt ra ngoai mgch t^o ra song di?n
tir. Khi cae ban eiia ty di^n l^ch nhau 180° thi kha nang phat song ciia m^ch la
Ian nhat.
Trong thyc te, nguai ta chi diing mpt day dan dai c6 cupn cam a giira, dau tren
de ha va dau duai tiep dat. Day nay gpi la Sngten. Angten la bp ph^n nim a loi
vao ciia may thu va a loi ra ciia may phat. Angten la m^ch dao dpng ha.
+ Nguyen tSe phat song di^n tir dya vao sy birc x^ song di^n tir.
+ Nguyen tSc thu song di$n tir dya vao sy cpng hirang dif n tir.
X . Nguyen tSc truyen thong bSng song di^n tir:

Quy trinh chung:
+ Bien cac am (ho$c hinh anh) thanh cac dao dpng di?n tan so thap, gpi la am
tan (ho^c thj tan).
+ "Trpn" cac dao dpng tren vao song di?n tu eao tan, ta dupe dao dpng di^n
duy trl vai tan so cao nhung bien dp thi bien thien theo dao dpng di?n am tan
(qua trinh nay con gqi la bien di^u bien dq ) . Song di^n tir da bien dif u (gpi
la song mang) sg mang cae tin hif u am tan di xa thong qua anten phat.
16


+ Dung anten de thu song di?n tir cao tan.
+ M^ch chpn song mic vai anten tren se chpn Ipc de thu song di?n tir muon
thu (m^ich nay la khung dao dgng LC va ho^t dgng d^ra tren s\f cpng huomg
difn).
+ Dung m^ch tach song cao tan va am tan.
+ M^ch khuech d^i dao dpng am tan nh^n dugc va loa phat am nh^n dugc.
XI. Song di^n tir va thong tin v6 tuyen:
+ Song dai (buac song A> 1 km): it bj nuoc hap thu nen dugc dCing de thong
tin duai nuoc.
+ Song trung (bir&c song X tir 100 m den 1000 m) : ban ngay bj tang di^n l i
hap thy m^nh nen khong truyen di xa dugc ; ban dem bj tang di?n li phan x?i
nen truyen di xa dugc.
+ Song ngan (biroc song A tir 10 m den 100 m): co nang lugng Ion va it bj
khong khi hap thy, bj phan x^ lien tiSp nhieu l£in giua tang di?n li va m§t d4t.
Cac dai phat song ngan cong suat Ion co thk truyen song nay di mgi noi tren
mjt dat.

!

+ Song cu-c ngan (btr&c song X tir 0,01 m den 10 m) : co nSng lugng 1cm nhat,

khong bj tang di^n li hap thy hoSc phan x?, co kha nang truyen di rat xa theo
duong thing va dugc dung trong thong tin vu try.
Dai truyen hinh dung cac song eye ngin. Song nay khong truyen dugc xa
tren m^t dat, phai diing cac dai tiep song trung gian ho$c cac v^ tinh nhan
t^io de thu song cua dai phat roi phat tra ve trai dat.
Cac dai phat thanh thuong dung song trung, song ng4n va ca song eye ng§n
(dai FM).

DONG DIEN XOAY CHII^U
I. Cach tao dong dif n xoay chieu (Dif n ap dao d^ng dieu hoa):
. Dya vao hi?n tugng cam ung di?n tir
Cho mgt khung day dan di^n tich S va co N vong day, quay deu quanh mgt tryc
I

doi xung xx' ciia no trong mgt tir truong deu B ( B vuong goc voi xx') vai v ^
toe goc CO. Theo djnh lu^it cam ung d i | n tir, trong khung xult h i | n mgt suat dif n
dpng cam ung: e = EoCOs(CL)t + cpo)
V | y : Suat difn dgng trong khung biln thien dieu hoa vai tan so goc co va gay ra
a hai dau khung mgt difn ap xoay chieu: u = UoCOS (cot + cpu)
+ Khi noi m^ch tieu thy vao di^n ap xoay chieu u = UoCOs(cot + cpu) thi trong
m^ch CO dong di^n xoaygbicu i , ~ IoCO3((0t i 17


Vay : Dong di^n xoay chieu la dong di^n c6 cuong dp bien thien dieu hoa
theo phuong trinh i = Iocos(cot + (p,)
(Trong do : i la cu&ng dQ tiec thai, lo la cu&ng dQ circ dgi ; co va (p, la cdc
hang sS).
Ta thdy di^n dp l^ch pha so vai ddng di^n gdc (p = % - (p, ; dQ l?ch pha nay phu thuQC linh chat cua mach di^n.

Cuong dp h i | u dyng ciia dong di$n xoay chieu bSng cuong dp ciia mpt dong
di|n khong doi ma neu chung Ian lupt di qua mpt di?n tro trong nhung thai
gian nhu nhau thi chiing toa ra nhung nhift iupng bSng nhau.
D9 Ion cua circmg

hi^u dung:

\k tac dyng toa nhi^t trong thoi gian dai thi dong di?n xoay chieu i = locoscot
tuong duong voi dong di?n khong doi c6 cuong dp bang ^°
I
D$t I = —j= va gpi I la cuong dp hifu dyng cua dong difn xoay chieu.
V2
Tuong ty ta c6: Di^n ap hi^u dyng:

42

Suat difn dpng hifu dyng:

V2

Muon do cuong dp hi?u dyng ciia dong xoay chieu nguoi ta diing Ampe ke
cho dong xoay chieu. Nguyen t5c ho^t dpng cua no la dyra tren nhung tac
dyng ma dp Ion ti 1? voi binh phuong cuong dp dong difn (tac dyng nhi^t,
tuong tac giua hai dong di?n bang nhau)
I I . Doan mach xoay chieu chi c6 dif n trtf thuan:
* Lien

UR va i:

Di?n ap giua hai dau do^n mach chi c6 di^n tro thuSn bien thien dieu hoa

ciing tan so va cung pha voi dong di?n trong m^ch.
=> khi i = lQCOs(a>t + 9;) thi U R = UoRCOs((Ot + 9 j ) voi UQR = I Q R

* Gian do vecto

O

I I I . Doan mach xoay chieu chi c6

di^n :

* Dung kbang: Z(- = —^ voi C la di?n dung cua ty
toC
18


*

Lien hf Uc va i :
Di^n ap giua hai dau doan mach chi c6 ty di^n bien thien di^u hoa cung tan
so nhung tre pha hon dong di?n

^

=> khi i = Iocos(cat + (Pj) t h i

= Uoccos(tot + tpj - •^) v a i U o c ~ ^o^c

* Gian do vecta
O

Uoc

IV. Doan mach xoay chieu chi c6 cu9n thuan cam :
*

C a m khang:

*

Lien

= Leo v a i L la dp t y cam cupn day.

u va i :

Difn ap giua hai dau do^n m^ch chi c6 cupn cam bien thien dieu hoa cung
tan so nhung som pha hon dong di^n
=> khi i = Iocos(cot + 9 ) ) thi

.

= UoLCOs(cot + 9 1 + ^ ) ^^ri U Q L = IQ^^L

Gian do v e c t a :
UOL

o
V. Doan mach xoay chieu R L C :
Gia sir dong di?n xoay chieu qua do^n m^ch la: i = lo coscot

=>

UR = UoR coscot v a i

UOR = loR

UL = U o L C O s ( c o t + ^ )

vai

UOL = I O Z L

Uc = U o c C O s ( o ) t - ^ )

v a i Uoc = IoZc

Di?n ap giira hai dau doan m^ch A B la: u = UR + U L + U c
=>
*

Uo = UOR + UoL + Uoc
Quan

giira dif n ap va dong dif n:

Tir gian do vec ta, ta c6 : Ug =
^ U O = IO7R-+(ZL-ZC)'

yj^l^

+(UOL

~^OC)^

(1)

19


D9 If ch pha cp cua u doi vol i:
UOL-UOC_ZL-ZC

tan cp = •

U oR

V$y: Di?n ap giua hai dau do?in
m^ch RLC bien thien dieu hoa
cung tan so nhumg l$ch pha cp so
vai dong difn.
+ Neu coL >
+ Neu ooL <
+ Neu coL =

1
coC.
1

=>(p < 0 : u tre pha so vai i

(oC
1

=:>(p = 0 : u cung pha so vai i .

coC

Djnh lu^t 6m cho doan mach R L C :
D^t Z = ^R^ + ( Z L - Zc f
Tir(l)tac6

Uo = loZ

la tong tra cua do^n mach
(*)

; Chia hai ve cua (•) cho V2 ta dugc bieu

thuc djnh lu$t Om: I = —
* Hi?n tUQtig C9ng hirong trong do^n mach R L C :
Tir bieu thuc I = — , neu U xac djnh thi I „ „ khi Z „ i „ o
1
<=> coL = coC

2
<=>

CO =

1 u

f
1
—
LC- hay f ~ 27tVLC

ZL=

*

Luc nay :

+ UL = UcvauL = -uc
+

UR = U

+ Di?n ap hai dau m^ch cung pha vai dong di^n.
V L Cong suat cua dong dif n :
Cong suat trung binh cua dong difn cung la cong suat trung binh trong mpt chu
ki. Do do cong suat trung binh cua dong difn cung la cong su4t cua dong difn
xoay chieu.
P = UIcos(p

; P = RI^ hay P =—cos^cp
R

20


Vai coscp dirgrc ggi la

so cong suat cua m^ch:

cos(p = —=^ocoscp = —
U„
Z
* Doi voi doan mach xoay chieu R L C noi tiep:
+ Khi cos (p = 1 ((j) = 0 ) => P = UI: do^n m^ch chi c6 difn tra thuan R hay
do?in m^ch RLC c6 cpng huong.
+ Khi cos(p = 0 ( ( t ) = = ± ^ ) = > P = 0: do?in m^ch chi c6 cam khang ho^c dung
khang ho^c ca hai.
+ K h i O < c o s ( p < 1 (-^<(t)=> P = UIcoscp : cong suat tieu thy tren do^n m^ch nho horn cong suat
cung cap cho m^ch (UI).
* Doi voi doan mach xoay chieu bat ki:
Vai cung di?n ap U va cuong dp dong difn I , khi do^in m^ch c6 coscp cang
Ian thi P cang Ian. Neu coscp nho de cong suat van b^ng P va di?n ap hai dau
m^ch la U thi I phai Ian => khong c6 Igri (toa nhi^t nhieu). Trong thyc te thiet
bj su dyng di^n xoay chieu phai c6 coscp > 0,85.
V I I . May phat di^n xoay chieu 1 pha:
* Hai each t^o ra suat di^n dQng trong cac may dif n:
+ Tir truang c6 djnh, cac vong day quay quanh trong tu truang.
+ Tu truang quay, cac vong day d^t c6 djnh.
* May phat dif n xoay chieu 1 pha: gom hai bp ph$n ca ban.
+ Phan cam: t^o ra tu truang, thuang la nam cham dif n.
+ Phan ling: t^o ra suat di?n dpng cam ung, la mpt khung ciay g6m nhieu vong day.
Mpt trong hai phan c6 thk quay quanh mpt tryc gpi la roto, phan kia dung
yen gpi la stato. Cac cupn day ciia hai phhn dupe quan tren cac loi thep silic
de tang cuong tu thong qua cac cupn day. Cac loi thep nay dupe lam bing
nhung la thep mong ghep each di^n voi nhau dk tranh dong di$n Phuco.

Neu phan ung quay, nguai ta lay di?n ra ngoai bSng bp gop. Day la mpt h?
thong gom hai vanh khuyen gan vai hai dau khung va hai choi quet c6 djnh
ti len hai vanh khuyen de dua di?n ra m^ch ngoai.
* Tan so dong di?n xoay chieu do may phat ra :
60
(p : so cap cue cua roto; n : so vong quay ciia roto/phut)
21


V I I I . May ph^t difn xoay chieu 3 pha:
•

Dong di^n xoay chieu ba pha la mpt hf thong gom ba dong difn xoay ehieu
gay bai ba suat di^n dpng xoay chieu eo eiing bien dp, eung tan so nhumg
i^eh pha nhau timg doi mpt la 120°.

* Cau tao:
+ Stato la phan ung, gom ba cupn day giong nhau quan tren loi thep silic, d$t
Ifch nhau 120" tren vanh tron.
+ Roto la phan cam, la nam eham di^n.
Cac loi thep ciia roto va stato dupe lam bang nhung la thep mong ghep each
di?n voi nhau de tranh dong di?n Phuco.
Hoat d9ng: Dya tren hi?n tuprng cam urng di^n tir.
Luc eye bac cua roto doi difn cupn 1 thi tir thong qua cupn 1 eye dai. Roto
phai quay them 1/3 chu ky thi tir thong qua cupn 2 eye d^i va quay them 1/3
chu ky nua thi tir thong qua cupn 3 eye dai. Nhu vay tir thong qua cac cupn
day l^ch nhau 1/3 chu ky ve thai gian hay 120° ve pha.
Tuang ty suat di?n dpng trong ba cupn day cung l^eh pha nhau 120°.
Neu noi ba cupn day vdi ba m^ch ngoai giong nhau ta c6 ba dong di^n xoay
chieu CO ciing tan so, cung bien dp va l?ch pha nhau 120°.

ii = lo coscot ;

i2 = lo cos © t -

27t

3

is =

lo

cos Q)t +

271

* L T U diem cua dong di^n 3 pha :
Tao tCr truang quay de sir dyng trong dpng ca khong dong bp 3 plia.

-

Bang each mac hinh sao hay tam giac, khi tai di?n ta tiet kifm dupe day dan.

-

I X . D^ng CO- khong dong b?:
+ Dpng ca di^n xoay chieu la thiet bj bien doi di^n nang cua dong di?n xoay
chieu thanh ca nang .
+ Nguyen tic ho^t dpng: Dya tren hi?n tugmg earn ung di?n tir va vi?e sir dyng
tir truang quay.

* Nguyen tac cua sy quay khong dong b9 :
Quay deu vai v^n toe goc oi mpt nam cham hinh chir U quanh tryc xx' de tao
ra tir truang quay. Trong tir truang quay nay d^t mpt khung day kin c6 ciing
tryc quay xx'. Khi nam cham quay, tir thong qua khung bien thien lam xuat
hi^n mpt dong difn cam umg trong khung, tac dyng cua dong nay la chong
l^i sy bien thien cua tir thong. Lyc di?n tir tac dyng len khung lam no quay
ciing chieu vai nam cham vai v^n toe goc cOo < co vi neu khung day quay da!
v^n toe CO thi lyc di^n tir mat di va khung day se quay ch^m lai.
Dpng ca ho^t dpng theo nguyen tac tren gpi la dpng ca khong dong bp.
22


* Tao tir tru-oiig quay bang dong di?n ba pha :
Cho dong di$n ba pha vao ba cupn day giong nhau d^t l?ch nhau 120° tren •
mpt vanh tron. Dong di?n ba pha qua ba cupn day da tao ra tir trircmg B c6
dp Ion khong doi va quay trong m§t phSng song song vol ba tryc cupn day
vai v^n toe goc co (hay v&i tan so bang tan so cua dong di^n).

* Cau tao cua d9ng ca khong dong bg ba pha :
Gom hai phan chinh :
+ Stato : Gom ba cupn day cua ba pha di?n quan tren loi sat d§t i|ch nhau
120° tren vanh tron de t^o ra tir trucmg quay.
+ Roto : Hinh try t^o bai nhieu la thep mong ghep l ^ i . Trong cac ranh xe a
mjt roto CO dat cac thanh kim io^i. Hai dau moi thanh noi vao cac vanh
kim loai thanh chiec 16ng. Long nay each di$n vai loi thep va c6 tac d\ing
nhu nhieu khung day dong tryc d§t l?ch nhau. Roto nay gpi la roto long
soc.
Khi mSc dpng ca vao m^ng di?n ba pha, tir truang quay do stato tao ra se
lam roto quay tren tryc. Chuyen dpng quay ciia roto vai v^n toe nho han
v$n t6c quay cua tir truang dupe tryc may truyen ra ngoai de v§n hanh

cac may ho$c ca cau khac.
+ Cong suat tieu thy cua dpng ca 3 pha hkng cong suat tieu thy ciia ba cupn
day a stato cpng l^i.
+ Hi$u suat dpng ca la ti so giua cong ca hpc Pci ma dpng ca sinh ra vai
p.
cong tieu thy P ciia dpng ca: H =
ifu diem cua dpng car khong dong bp 3 pha :
+ Cau tao don gidn, de che tao.
+ Sit dung ti^n l^ri, khong can vanh khuyen, choi quet.
+ Co the thay doi chieu quay de dang.
So sank Roto va Stato cua may phdt di^n xoay chieu 3 pha vd dpng cff khong
dong bp 3 pha :
+ Stato giong nhau: gom 3 cupn day giong nhau dat l?ch nhau 12(f tren mpt
gid tron.
+ Roto khac nhau: May phdt di^n co Roto Id nam chdm con dpng ca di?n co
Roto Id hinh tru tdc dung nhu mpt cupn day quan tren loi thep.
Nhu vgy mudn bien dpng co di^n thanh may phdt di^n ta chi can thay Roto
ciia dpng ca bang mpt nam chdm di^n.

X. May bien ap :
La thiet bj bien doi di?n ap ciia dong di?n xoay chieu.
23


www.matheducare.com
Cau tao :
M p t loi thep hinh khung chS nhat gdm nhieu la thep mong ghep each di?n
v o i nhau.
Hai cupn day dong c6 so vong khac nhau quan tren loi thep. M p t cupn noi
v o i m^ng di?n xoay chieu gpi la cupn so cap. Cupn kia noi v a i tai tieu thy

gpi la cupn thur cap.
Hoat d9ng : D y a vao hi^n tupug cam ung di?n tit.
Dong di^n trong cupn so cap larri phat sinh mpt tir truong bien thien trong
loi thep. T u thong bien thien ciia tir truong do gay ra mpt suat di^n dpng cam
ung xoay chieu trong cupn t h u cap va mpt dong d i f n cam ung xoay chieu o
tai tieu thy.

S\ bien doi di^n ap va cirong d9 dong dif n :
Gpi
U i va U2 la di^n ap hi^u dyng 2 dau cupn so cap va t h u cap.

+

N i va N2 la so vong day ciia cupn so cap va ciia cupn t h u cap

+

^
,
Ta co:

U2

=

N,

* Sy bien doi cuoug dy dong di^n :
K h i m^ch t h u cap noi v a i tai. V i hao phi nang lupng trong bien ap rat nho
nen :

P, =P2 O U , I , = U 2 l 2 0

— = —
Uj
I2

Vay: ^
+

T i so di^n ap a hai dau cupn t h u cap va cupn sa cap bang t i so vong day
hai cupn.

+

K h i dung may bien ap di?n ap tSng bao nhieu Ian thi cuang dp dong di?n
giam bay nhieu Ian.

* Cong dung may bien dp:

Han di^n, ndu chdy kim

+

Tang di4n dp khi truyen tai di^n nang de giam hao phi.

+

Bien doi di^n dp thick h(rp vai nhu cdu.

+

logi...

X I . Truyen tai dif n nSng :
D i f n nSng san xuat tir nha may di^n dupe truyen tai den nai tieu thy nha ducmg
day dan.
P
+ Cong suat tai di tren duang day dan P = Ulcos(p <=> I =
Ucoscp
I Id cuang dq dong di?n tren day)
(vai U la di^n dp a dau duang ddy;

24