Luyện thi cấp tốc các dạng bài tập từ các đề thi quốc gia môn vật lý(NXB đại học sư phạm 2011) phạm đức cường phần 1

530.076
pHAM
DLfC
CLfdNG
(Chu
bien)
L527TH
E TAN Rl - BUI
IRAN
DLfC
ANH
THAI,
THAN
THANH
SANG
CAC
DANG
BAI TAP TQ CAC DE THI
QUOC
GIA
(TOT
NGHI
EP
- TUYEN k
/
INH)
VAT^Y
^ Cac de chinh
thiic
va de luy^n tap
p an va thang diem

ciia
BQ Giao due va Dao tao
(Tai ban,
svfa
chvTa
va bo
sung)
Cho mach dien
xoay
chieu
nhif
hinh
ve. Bi^t cuon day c6 dien trd khong
~ dang ke. Khi khoa k dong dong dien qua mach cham pha hofn dien ap hai
_
d^u
mach la —. Khi 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. ZL = (V3 + DZc
M
C. Z:. = ^
DVL011170
D. ZL = (73- DZC

NHA
XUAT
BAN DAI HOC Si/
PHAM
LE TAN Ri -
PHAM DLfC CLfdNG (Chu
bien)
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

LY
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; Via;
TNVH
BiNH
VHUAW
NHA
XUAT
BAN DAI HQC Si/
PHAM
MUC LUC
Phan
1: Tom tat
giao
khoa
A.
Phan chung cho
cce
ban va nang cao
Dao dpng ca 3
Song ca 6
Dao dpng di^n tir - song

difn
tir 13
Dong
di?n xoay chieu 17
Song anh
sang
25
Lugng
tir anh
sang
31
H^t
nhan nguyen tir 37
Tir
vi
mo den
vT
mo 43
B.
Phan rieng cho chirong trinh nang cao
Dpng
lyre
HQC
vat ran 49
Con
lac
v§t
K
53
Hi?u

img Dop-ple 53
Thuyet tuong doi h^p 54
Thuyet Big bang 56
Phan
2:
Kien
thirc can nhor
A.
Phan chung cho co ban va nang cao
Dao dpng
CO
58
Song ca 64
Dong
di?n xoay chieu 66
Dao dpng di^n tu 69
Song anh
sang
70
Quang di^n 73
Vat
li
h^t nhan 74
B.
Phan rieng cho chirong trinh nang cao
Ca hpc v^t ran 77
Con
lac
v§t
li

80
Hi?u
irng
Dop-ple 80
Quang di$n 80
Tia
X (Ronghen) 82
Phan
3: Dap an va huoTig dan giai cac de on luyfn Tu Tai 83
Phan
4: Dap an va hv&ng dan giai cac de on
luyf
n
Dai h9c - Cao dang 190
^han t: TdM TAT
GIAO
KHOA
Phan chujif cho ban of ban ad ndn^ eao
DAO
DONG
CQ
I.
Dao d9ng dien hoa :
*
Dao dpng tuan hoan la dao dpng ma trang thai chuyen dpng cua vat
dupe
l$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 = -kx
+
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
= 2n-
Vg
*
Hf 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
IV.
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
CO
tin 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
vin
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.
Sy
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
CO
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 tin 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
+2AiA2COs(92
+ Pha ban dau hai dao dpng tong hpp la 9, voi:
taiKp^
Aisincpi
+
A^sincp;
AiCOSCpi
+
A2C0S(P2
+
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
= A| - A2 ;
cp
=
(pi
neu Ai > Aj
Noi
chung :
A,
-A2 < A<A, +A2
SONG
ca
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.
Trong
rnqt
moi
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 tii
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 ti I9 vai binh phuomg bien dp
song
tai
diem do. Mpt 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.
III.
PhiroTig trinh song :
Xet
song
truyen tir nguon O den diem M
each
O mpt doan OM = 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: UMCO =
Uo(t
- to)
Uyj

= Acos(©t-^)
hay
UM
= Acoscot-Y'') (*)
(•) cho ta xac djnh li dp ciia phan tur
song
t^i
diem M bat ki 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: = Acos(— t + — x)
Tir
(*) ta thay
song
c6 hai
tinh
chat:
+
Tinh
tuan hoan theo thoi gian:
Khi
xet mpt diem P tren
song
c6 toa dp x = d.
Ta thay li dp u cua P bien thien theo ham cos => chuyen dpng cua diem P la

mpt
dao dpng tuan hoan vai chu ki T = —.
(0
+
Tinh
tuan hoan theo khong gian:
Khi
xet tat ca cac diem tren
song
vao thai diem to,
(*)
"M =
Acos(
Y to - Y x)
Ta thay li dp u cua cac diem tren
song
bien thien tuan hoan theo li dp x =>
hinh
dang
song
(hinh
sin) tai thai diem to : cu sau mpt
buac
song
thi
song
lai
CO
hinh
dang nhu truac.

7
D^c bift:
+ NhiJng diem
tren
phuong
truyen
song dao dgng cung pha vai nguon khi
— x = 2k7i=> x = kX vai Ikl =0,1,2,
+ Nhung diem
tren
phuang
truyen
song dao dpng ngugc pha vai nguon khi
— x = (2k+
1)71=^
x = (k + -)X
A. 2
IV.
Phan xa song:
Song dang
truyen
trong mpt moi
truong
ma g^p v§t can thi bj phan x^. Song
phan
X9
c6 ciing tan so va buac song ciia song tai.
+ Neu v$t can c6
djnh
thi song phan x^

luon luon
ngugc pha vai song tai a
diem
phan x^.
+ Neu v^t can tyr do thi song phan x?
luon luon
ciing pha vai song tai a
dilm
phan
x^.
V. Song dirng:
Song dCmg la song c6 nhCrng diem dung yen (nut
song)
va nhOng diem dao
dgng vai bien dp c^rc d^i (byng
song)
trong khong gian.
Dac
dilm :
+ Song
diing
la svr
giao
thoa giua song tai va song phan x^
tren
cdng phuang.
+ Vj
tri
cac nut va cac byng la c6
djnh.

- Vj tri cac nut
luon
each diu c6
djnh
nhirng
khoang bSng mpt so nguyen
Ian
nua buac song.
- Vj tri cac byng
luon
each dau c6
djnh
nhung
khoang bSng mpt so le l4n
mpt
phan tu buac song.
3l
+ Khoang each giua hai nut
(ho$c
hai
byng)
ke
nhau
dfiu
bSng —.
Dieu
kif
n
c6 song dirng:
- Khi 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.
- Khi mpt dau day ty do va mpt dau day c6 djnh: De c6 song dung, chieu
dai
spi day bang so nguyen le Ian mpt phan tu buac song
l = m— (vai m = 1, 3,
5 )
4
=> 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:
UA
=
UB
= 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:
U2
= Acos(cot - )
K
Dao dpng
t^i
M la tong hpp cua hai dao dpng tren.
2nd,, , , 2nd,,
u
= u, +
U2
= Acos(cot -) + Acos(cot -)
7t(d2-d,)
o u = 2Acos—^^^^
*^cos
cot-
7t(d2
+d,)

V$y
dao dpng
t^i
M la dao dpng dieu hoa
voi
bien dp :
A
^2
A
cos-
Ta
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 :
7t(d2-di)
=
2kK)
khi : cos
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).
=
1
o 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 = 0 (hai dao dgng thanh phan ngu^c pha :
7t(d2-d,)
A(p
= (2k
+
l)7t) khi : cos
=
0
d2
-d, = (k + 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.
VIL
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 la mpt d§c
tinh
c6
hiru
cua song, giong hi?n tupng giao
thoa song.
VIII.
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.
-
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.
-
Song am ma tai nguai
CO
the cam thy
dupe
CO
tan so tir 16 den 20 000
Hz,
con gpi la am thanh.
-
Song sieu am la nhirng song ca hpc co t^n s6 f > 20 000 Hz
-
Song ha am la nhirng song co hpc co tan s6 f < 16 Hz
+
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

truyen
dugc
trong
tSt ca cac moi
truong
khi, 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 di vai toe dg xac
djnh.
* Toe d9 truyen am phu thugc :
-
Tinh
dan h6i va
khdi
lugng rieng cua moi
truong.
- Nhi$t dg ciia moi
truong.
Noi Chung 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
* Tap am: la nhung song am khong c6 tan so xac
djnh,
c6 do thj dao dgng la
nhung
duong cong khong tuan hoan. Vi du: tieng may no
IX:
Cac dac trimg
sinh
ly cua nhac im :
* D9 cao cua am:
La mgt dac
tinh
sinh ly cua am, gSn
lien
voi 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.
Am
cang cao khi tan so cang Ion, nhung dg cao ciia am khong ti I9 vai tin so.
* Am 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:
+ Am sac la mgt d$c
tinh
sinh li ciia am giup ta phan bi?t dugc cac am cung dg
cao nhung phat ra tu nhiJng nguon khac nhau.
+ Am sic dugc
hinh
thanh dyra
tren
tan so va bien dg am.
+ Am sac gan
lien
vai d6 thi dao dgng am. Am sac khac nhau khi 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 ti 1^ voi
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:
-
Tai nguai phdn bi?t dugc hai dm
c6
mice
cuong
dQ
chenh l^ch nhau
it
nhdt la
I
dB.
-
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.
-
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
I.

bdng
130 dB
(L„ax
= lOlg-^ = 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|
(voik=
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-
(vaim=
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 dl 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.
II.
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 +
<p
+ )
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
:
W<i
=
—
Cu"^
= — cos^ (cot + 9)
Nang 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.
+
Ning
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 di|n tir do may phat
ra bang tan so rieng cua m^ch
LC:
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.
CO
buac
song
trong
chan
khong la
+
+
XI
(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.
IX.
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
li
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 di|n
tir,
trong
khung
xult
hi|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 <p,)-
THI/ VIEW TlrJHBiNH THUAN
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
<p
nay phu
thuQC
linh
chat
cua
mach
di^n.
Cuong dp hi|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)
II.
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
UR
= UoRCOs((Ot + 9j) voi UQR = IQR
*
Gian do vecto
O
III.
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) thi =
Uoccos(tot
+ tpj -
•^)
vai Uoc ~ ^o^c
*
Gian do
vecta
O
Uoc
IV.
Doan mach xoay chieu chi c6 cu9n thuan cam :
*

Cam
khang:
=
Leo
vai L la dp ty cam cupn day.
*
Lien
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
+ 91+^)
^^ri UQL
=
IQ^^L
Gian do
vecta:
UOL
o
V.
Doan mach xoay chieu
RLC:
Gia sir dong di?n xoay chieu qua do^n m^ch la: i = lo
coscot
=> UR

=
UoR
coscot
vai
UOR
= loR
UL
=
UoLCOs(cot+^)
vai
UOL
=
IOZL
Uc
=
UocCOs(o)t-^)
vai Uoc =
IoZc
Di?n
ap
giira
hai dau
doan
m^ch AB la: u =
UR
+
UL
+ Uc
=> Uo =
UOR

+ UoL + Uoc
*
Quan
giira
dif
n
ap va
dong
dif n:
Tir
gian do vec ta, ta c6 : Ug =
yj^l^
+(UOL
~^OC)^
^UO
=
IO7R-+(ZL-ZC)'
(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.
1
+
Neu
coL
>
+
Neu
ooL
<
+
Neu
coL
=
coC.
1
(oC
1
coC
=>(p
< 0 : u tre pha so vai i
=:>(p
= 0 : u cung pha so vai i.

Djnh
lu^t 6m cho doan mach
RLC:
D^t
Z = ^R^ +
(ZL
-
Zc
f la tong tra cua do^n mach
Tir(l)tac6
Uo = loZ (*) ; Chia hai ve cua (•) cho V2 ta
dugc
bieu
thuc djnh lu$t Om: I = —
* Hi?n
tUQtig
C9ng
hirong trong do^n mach
RLC
:
Tir
bieu thuc I = —, neu U xac djnh thi
I„„
khi
Z„i„
o
ZL
=
1
2 1 u f 1 *

<=> coL
= <=> CO =
—-
hay f ~
coC
LC
27tVLC
Luc
nay :
+
UL
=
UcvauL
= -uc
+
UR = U
+
Di?n ap hai dau m^ch cung pha vai dong di^n.
VL
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

RLC
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.
+
KhiO<cos(p<
1
(-^<(t)<Oho$c 0<(|)<-^)
=>
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.
VII.
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
VIII.
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
is = lo cos
Q)t
+
271
3
*
LTU
diem cua
dong
di^n 3 pha :
-
Bang
each
mac
hinh
sao hay tam giac, khi tai di?n ta tiet
kifm
dupe
day dan.
-
Tao
tCr
truang quay de sir dyng trong dpng ca khong dong bp 3
plia.
IX.
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
Cau
tao :
Mpt
loi thep
hinh

khung chS nhat gdm nhieu la thep mong
ghep
each
di?n
voi
nhau.
Hai
cupn day dong c6 so vong
khac
nhau quan tren loi thep. Mpt cupn noi
voi
m^ng di?n
xoay
chieu gpi la cupn so cap. Cupn kia noi vai tai tieu thy
gpi
la cupn thur cap.
Hoat
d9ng
: Dya 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. Tu thong bien thien ciia tir truong do gay ra mpt
suat
di^n dpng cam
ung
xoay
chieu trong cupn thu cap va mpt dong
difn

cam ung
xoay
chieu o
tai
tieu thy.
S\
bien
doi di^n ap va
cirong
d9
dong
dif n :
Gpi
+ Ni va N2 la so vong day ciia cupn so cap va ciia cupn thu cap
+ Ui va U2 la di^n ap hi^u dyng 2 dau cupn so cap va thu cap.
^ , U2 N,
Ta co: =
* Sy
bien
doi
cuoug
dy
dong
di^n :
Khi
m^ch thu cap noi vai tai. Vi hao phi nang lupng trong bien ap rat nho
nen :
P, =P2 OU,I, =U2l20 — = —
Uj
I2

Vay: ^
+ Ti so di^n ap a hai dau cupn thu cap va cupn sa cap bang ti so vong day
hai
cupn.
+ Khi 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:
+ Bien doi di^n dp thick h(rp vai nhu cdu.
+ Tang
di4n
dp khi truyen tai di^n
nang
de
giam
hao phi.
+ Han di^n, ndu
chdy
kim logi
XI.
Truyen tai dif n
nSng
:
Difn
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
(vai U la di^n dp a dau
duang
ddy; I Id cuang dq
dong
di?n tren day)
24