Huong dan gidi: Khoang each giua hai diem gan nhau nhat tren ciing mpt phuong truy^Y, song dao dpng ngupe pha nhau la: d = X/2 = 1 m.. Khoang each giiia hai diem gan nhau nhat tren cun
Trang 1I tnuat gtat ttnann m iisi vat L t i^, tap I - Nguyen Quang Lac
Vai may FX570-ES ta bam n h u sau :
,y [MODEJ § t r e n m a n h i n h x u a t h i # n c h u : CMPLX
|SHIFTJ|MOD£| § chuyen doi don vi do goc la R (Rad):
fi! |4>/3|^HIFTJ 0 § g § ISHIFTJ 0 H • • j h li jisv'v' :jr
[SHIFT] 0 § 0 '^^'^ ^^^^ '^^t 4 Z 7t/2
Nghia la bien do bang A = 4; pha ban dau cf) = n/2
=> Chon A
Cau 146 Mot vat thuc hi^n dong thoi hai dao dpng dieu hoa cung phuong c6
phuong trinh dao dong la X j =4sin(7tt + a) (cm), = 4\/3cos7ct (cm) Bien do
dao dong tong hop dat gia tri nho nha't khi
mot true Ox c6 phuong trinh: xi = 4cos c o t - ^
3 j cm; X2 = A2cos(o)t + (p2)cni
Phuong trinh dao dong tong hop x = 2cos((ot + (p)cm Trong do cpj -(p =
Cap gia tri nao cua A2 va cp sau day la dung?
A sVScm; - B 2V3cm; - C sVScm; 0 D 2V3cm;0
2 4
Huong dan gidi: ^T^^->
Bieu dien cac dao dong tren gian do vec to,
ta c6: OA = Ai = 4cm; OB = A2; OC = A = 2cm
Tu gian do vec to suy ra:
BC2 = O C + OB2
A? + A^ + A^ => A2 = - A ^ = V42 -2^ = 2V3 (cm) Mat khac: A^ = A^ + A^ + 2A^Aj cos(92 - 9])
o 2^ =4^+(2V3)%2.4.2N/3COS n 71
I 3 ; cos 571
6 J 2 ' V P •cp = 0
Vay A2 = 2\/3(cm); (p = 0 => Chpn D 0ii_148 Mot vat thuc hien dong thoi 2 dao dong c6 phuung trinh la
Xj = 4^2 sin27it(cm); X2 = 4>/2 cos27it (cm) Ket luan nao sau day la sai? , >
A Bien dp cua dao dpng tong hpp la A = 8cm iML.'''i^ \
B Tan so ciia goc dao dpnh tong hpp co = 27t rad/s , ;
C Pha ban dau cua dao dong tong hpp 9 = —
4
D Phuong trinh cua dao dpng tong hpp x = 8cos
4 c m
Huong dan gidi:
Taco: x, = 4V2sin27it(cm) va X j = 4\/2cos27tt (cm) A
Vi hai d a o d p n g t h a n h phan deu co tan so goc co = 27irad/s nen dao d p n g tong hpp cOng co tan so goc (a = 2n rad/s dap an B d i i n g
Bien d p ciia d a o d p n g tong hpp xac djnh:
Voi may FX570-ES ta bam n h u sau :
P O D E ] ^ tren man hinh xuat hien chu: CMPLX
| H I F T ] [MODEJ § chuyen doi don vi do goc la R (Rad):
7-
f72 S H I F T (-) -7t/2 S H I F T (-) 0
161
Trang 2- SHIFT] y g y M a n hinh hien thi ket qua: 8 Z -7t/4
NghTa la bien do bang A = 8; pha ban dau 4> = - H / 4
A diing ; B diing ; C diing ; D sai ^ Chon D
C a u 149. M g t vat tham gia dong thai hai dao dong ciing phuong, cung tan so
C O bien do Ian lug-t la A i = 3cm va A 2 = 4cm Bien do dao dgng tong hop khorig
the nhan gia tri nao sau day:
A 5,7cm B 1,0cm C 7,5cm D 5,0cm
Huong dan gidi:
Theo p h u o n g phap gian do vec to Fre-nen thi bien do dao dpng tong h o p
luon phai thoa man: |Aj - A j | < A < A j + A j Theo bai ra, ta c6:1cm < A < 7cm
Vay A khong the bang 7,5cm => Chpn C
C a u 150 M o t vat thyc hien dong thoi hai dao dong dieu hoa ciing phuong,
cimg tan so' i = 4Hz, ciing bien do 5 cm va c6 do lech pha A(p = — Cho 7t^ = 10
Van to'c ciia vat khi no c6 gia toe 32>/2 (cm/s^) la
C a u 151 Cho hai dao dpng dieu hoa ciing phuong: X j = Acos
cm (t do bang giay) Bie't phuong trinh dao dpng tong hop
X 2 = Bcos c o t - ^
2
la X = 5cos(cot + (p)(cm) Bien dp dao dpng B c6 gia tri cue dai khi A bSng:
A 573cm B 5 cm C Syflcm D 2,5V2cm
, Hwang dan gidi:
Tir cong thiic tong hop dao dpng ta c6:
571 5^ = A^ + B^ - 2 A B C O S — hay A^ - VSBA + B^ - 2 5 = 0
6
De p h u o n g trinh (1) c6 nghi^m A voi B la tham so thi:
(1)
A = ( V 3 B ) ^ - 4 ( 5 2 - 2 5 ) > 0 <=>B<10(cm)
Bmax = lO(cm) thay vao (1) ta dupe A = S^/Scm => Chpn A
M p t con lac 16 xo tham gia dong thoi 2 dao dpng dieu hoa ciing
phuong, ciing tan so' co = 5\f2 rad/s, c6 dp If ch pha bang ^ Bien dp ciia 2 dao
dpng thanh phan la A i = 4 cm va A 2 Biet dp Ion van toe ciia vat tai thoi diem (Jpng nang bang the nang la 40( cm) Bien dp thanh phan A 2 bang
A. A 2 = 4 cm B. A 2 = 4 V 3 cm C. A 2 = \/3 cm D. A 2 = 6 cm
Huang dan gidi:
Ta C O co nang ciia vat: E = W j + W, = ^ k A ^
Khi dpng nang bang the nang, ta co:
E = 2W^ = i k A 2 = > 2 - m v 2 = i k A 2
d 2 2 2
A ^ = 2 - - 2v^ • A = 8cm Mat khac ta co:
A ^ = A J + A ^ + 2 A 1 A 2 C O S ( A 9 = A ^ + A ^ )
^ Al=A^-Al=8^-A^=>A2 =4Scm
=> Chpn B
C a u 153 Cho hai dao dpng dieu hoa cimg phuong: X j = 2 c o s ( 4 t + (pj)cm;
=2cos(4t + (p2)cm v o i 0 < (P2 -(Pj ^ n Biet phuong trinh dao dpng tong
'ff': Huang dan gidi:
Gian do vecto n h u hinh ve Ox la tri^c goc:
O A = O A i + O A 2 Theo bai: O A i = OA2 = 2 (cm)
=> Tam giac O A A 2 can tai O => O A A 2 = O A 2 A
O A la phan giac A j O A 2 (Vi OA2AA1 la hinh thoi)
Trang 3Cau 154 Mgt vat tham gia dong thai hai dao dong dieu hoa cung phuang v6,
X j =4cos^5>/2t-njcm va X 2 = A 2 C O S 5\ll\ — cm, trong do t tinh bang
giay Biet dp Ian van toe ciia vat tai thoi diem dpng nang bang the nang ij
40cm/s Hay xac djnh bien do dao dpng thanh phan Aj ?
A VScm , ,^ B 2V3cm C 373cm D 4V3cm
Huang dan gidi:
Khi dpng nang bang the nang ta c6: 2Ed = E
Cau 155 Mot con lac 16 xo dao dpng tat dan Cu sau moi chu ki bien dp ciia no
giam 2,5% Phan nang lupng cua con lac bj mat di sau moi dao dpng toan
phan la
A 35% ^ B 45% C 55%
' ' ^ Huang dan gidi:
1 2 2
Nang lupng trong chu ki dau la: W = - mco A
Nang lupng trong chu ki tiep theo la: W ^mco^A'^
Cau 156. * Mot con IMc 16 xo c6 dp ciing k = 10 (N/m), khoi lupng vat nan?
m = 100 (g), dao dpng tren mat phang ngang, dupe tha nhe tu vi tri 16 xo d^^
6cm so voi vi tri can bang H? so ma sat trupt giua con lac va mat ban bang H *
Q 2- Thai gian chuyen dpng thling cua v|t m tu liic ban dau den vi tri 16 xo l^'hong bien dang la:
A
30
20 • 15
Huong dan gidi:
Vi tri can bang ciia con lac 16 xo each vi tri 16 xo khong bien dang x:
kx = fjmg => X = |Limg/k = 2 (cm)
Chu ki dao dpng: T = 2 7 t J ^ 0,2n (s) "^'•> •
-Thai gian chuyen' dpng thSng ciia vat m tu liic ban dau den v i tri 16 xo khong bien dang la: t = j + - ^ = -^(s) => Chpn C ' ^ ; rSu 157 * Mot con lac 16 xo gom mot vat nho kho'i lupng 0,02kg va c6 dp cung
1 N/m Vat nho dupe dat tren gia do c6 dinh nam ngang dpe theo trvic 16 xo
H? so ma sat trupt giiJa gia da va vat nho la 0,1 Ban dau giu vat 6 v i tri 16 xo
bj nen 10 cm roi buong nh^ de con lac dao dpng tat dan Lay g = lOm/s^ Toe dp
Ion nhat vat nho dat dupe trong qua trinh dao dpng la
A 1572cm/s B 25V2em/s C 40^^ cm/s D 50v^em/s
Huang dan gidi:
Van toe ciia vat dat gia trj Ion nhat trong qua trinh dao dpng tat dan ehinl"
v$n toe Ian nhat ma vat dat dupe trong i chu ki dau tien Gpi x la vi tri l i do
ma vat c6 toe dp Ion nhat
Ap dung dinh luat bao toan nang lupng, nang lupng ban dau ciia h§ gom the
nSng cue dai ban dau: ~ k A p , nang lupng ciia h§ tai thoi diem vat c6 van toe c i ;
?i gom dpng nang ^ m v ^ , the nang ^^x^ va dp Ion eong ciia lye ma sat:
y' = 0 » X = - 1 ^ ^ = -0,02m = -2em ' ,,
Trang 4Ki thuatgilii iiluiiih BI'rN Vat Li 12, t&p 1 - Nguyen Quang Lac
D o do do giam the nang la: AW, = - (A^ - ) = 0,048 J = 48 m j
Khao sat svt bien thien ciia y ta tha'y v o l x = -2cm thi y dat gia trj cue
Suy ra v dat gia trj eye dai tai v i tri x = -2cm
v ^ 3 ^ = J — A l ^ - — x 2 - 2 n g ( A l + x) = 0,4V2m /s = 40N/2cm /s
=> Chgn C
Cau 158 M p t con lac 16 xo nam ngang gom v^t nho kho'i l u g n g 200 (g), 16 xo
dp Cling 10 (N/m), h$ so ma sat trupt giua v$t va mat phSng ngang la 0,1 Ba^
dau vat dupe g i i i 6 v i t r i 16 xo gian 10 cm, roi tha nh? de con lac dao dpng tjj
dan, lay g = 10 (m/s^) Trong khoang thoi gian ke t u liic tha cho den k h i toe ^6
ciia vat bat dau giam thi dp giam the'nang ciia con lac la:
A 12mJ B 24mJ C 36 mJ D.48mJ
Huang dan gidi:
Vgt dat van toe cue dai khi Fdh = Fms
=> kx = ^ m g => X = ^^^^ = 2 (cm)
=> Chpn D
Cau 159 M p t tarn van bac qua mpt con m u o n g c6 tan so' dao dpng rieng bang
0,5 H z M p t ngu6i d i qua tam van v o i bao nhieu buoc trong 12s thi tarn van bi
rung len manh nhat?
A 8 buoc B 6 buoc C 4 buoc D 2 buoc
Huang dan gidi:
K h i buoc chan vao tam van thi chan nguoi da tac d u n g vao tam van mot
luc Muo'n tam van rung len manh nhat thi tan so'ciia lye tac d y n g vao tam van
phai bang tan so'dao dpng rieng ciia tam van
N Gpi N la so buoc chan: => — = 0 , 5 = > N = 6 buoc chan => Chpn B
Cau 160 M p t con lac 16 xo c6 dp ciing 100 N / m , vat nang c6 khoi l u p n g
lOOg-dao dpng tren mat phMng nam ngang so ma sat giua vat va m|it phang
ngang la fa = 0,02 Cho gia toe trpng truong g = 10 m/s^ Keo vat khoi v i tri caf
bang mpt doan 10 cm roi tha nh? Quang duong vat d i dupe cho den k h i dimr
han la:
A 25 cm B 2 5 m C 250 cm D 2 5 0 m
Huang dan gidi:
Co nang ciia vat la: W = ^ k A ^ = ^.100.0,1^ = 0 , 5 ( j )
Cfy TNHH Ml Kangvi^
{Chi vat d u n g h i n thi co nang cua vat chuyen het thanh cong ciia lyc ma sat
Do do: A ^ ^ = Hmg.s = W => 0,02.0,1.10.5 = 0,5 => S = 25(m)
= > C h p n B ' '
£^vi 161 M p t con lac lo xo nam ngang dang dao dpng tat dan N g u o i ta do
jju<7C dp giam tuong do! ciia bien dp trong 3 ehu ky dau tien la 8% D p giam
tuong doi ciia the'nang dan hoi tuong u n g
phang ngang la fa = 0,2 Lay g = 10 m/s^; n = 3,14 Ban dau vat nang dupe tha
nh? tai v i tri 16 xo dan 6 cm Toe dp trung binh ciia vat nang trong thoi gian ke
tu thoi diem tha den th6i diem vat qua vj tri 16 xo khong bi bien dang Ian dau tien la:
A 22,93em/s B 25,48em/s C 38,22cm/s D 28,66cm/s
Huang dan gidi:
Chpn Ox = true 16 xo, O = v j t r i ciia vat khi 16 xo khong bien dang, chieu duong la chieu dan ciia 16 xo
Khi vat chuyen dpng theo chieu am: - k x + famg = ma = m x "
Trang 5Vtb = 90
a 28,66 cm/s
7 t / 1 5 3,14
=> Ch(?n D
Cau 163 Mot con lac 16 xo dao dong tat dan cham Cu sau moi chu ki, bien do
dao dong cua no giam 0,5% Nang lugng dao dong cua con lac bi mat di sau
moi dao dong toan phan la
1< Vay nang lug-ng bi mat di la 1% => Chon B
Cau 164 Mot con lac don c6 dp dai lo = 16cm dupe treo trong toa tau a ngay v i
tri phia tren cua true banh xe Con lac dao dpng manh nhat khi van toe cua
doan tau bang 15 m/s Lay g = 10 m M 7t^ = 10, coi con tau chuyen dpng thang
deu, chieu dai moi thanh ray bang
A 12 m B 16 m C 18 m D 2 4 m
Huang dan gidi:
Chu ki cua lye cuong buc tac dung len con lac: T = —
Chu ki dao dpng rieng ciia con lac: TQ = 27t J —
V S
Con lac dao dong manh nhat khi T = 27iJ— = - ==> 1 = 2n, : ^ v = 12m
8
=> Chpn A
Cau 165 Mot 16 xo c6 dp cung k = 600N/m, mot dau co'dinh, dau kia gan qun
cau nho khoi lupng m = 300g, qua cau c6 the trupt tren mot day k i m loai cang
ngang trung voi true 16 xo va xuyen qua tarn qua cau Keo qua cau ra khoi vj
tri can bang 2cm roi tha cho qua cau dao dpng Do c6 ma sat nho, dao dpng
ch^m dan, sau 200 dao dpng thi qua cau dung l ^ i Lay g = 10m / Dp giam
[jjen '^^ dpng toan phan va h$ so'ma sat giiia qua cau voi day kim ila
Huang dan gidi:
f a tim bieu thue ciia dp giam bien dp sau moi dao dpng toan phan
Gpi A i , A 2 la bien dp dao dpng tai hai thoi diem each nhau nira dao dpng
£)p giam CO nang cua con lac: AW = ^ k ^ A j - A j Congcua lire ma sat: AA^^, = F ^ , { A J + A 2 ) = nmg(Ai + A 2 )
Do AW = A A ^ , = > A j A 2 = ^
-Dp giam bien dp trong moi dao dpng: AA = 2 ( A J - A 2 ) =
Theo bai ra: 200AA = AQ = 2cm
T u d o : AA = r T r = 0,01cm va n = - ^ = 0,005 Chpn C
4|img )' ^ '
200 4mg
CSu 166 Mot con lac 16 xo dat tren mat phSng nghieng goe ao = 60" so voi mat
ngang, h^ so' ma sat gii>a vat va mat phang nghieng la | i = 0,1, vat c6 khoi lupng m = 400 (g), lay g = 10 m/s^ Cong suat can cung cap cho con lac de no dao dpng dieu h6a voi bien dp A = 5cm va tan so f = 6 Hz la:
A P = 180(mW) B.P = 200(mW) C.P = 220(mW) D P = 240(mW)
Huang dan gidi:
Sau khi cung cap bu nang lupng cho vat thi vat se dao dpng dieu hoa:
Cong cua lire ma sat tieu hao sau moi chu ky:
A^„^| = H.N.4.A = n.m.g.cos(a).4.A = 0,1.0,4.cos60.4.0,05 = 0,04(j) Nang lupng can cung cap sau moi chu ky la: , 1
§iif4 AW = IA^, I =0,04 0) Cong suat can cung cap: P = ^ = AW.f = 0,04.6 = 0,24 (w) = 240(mW) p=> Chpn D
J67 Mot dao dpng tat dan c6 bien dp giam 2% sau moi chu ki Sau 5 chu
Vi CO nang dao dpng c6n lai chie'm so'phan tram so voi co nang ban dau la: l-A 17,3% B 28.9% C 73,2% D 81,5%
Huang dan gidi:
Theo gia thie't sau moi chu ky bien dp giam 2% tue la: ,1
Trang 6Sau hai chu k y , ca nang con lai: = 0 , 9 6 W i = {0,9ef W
, Sau n a m c h u k y , ca nang con l a i :
W5 = ( 0 , 9 6 f W = 0,815W = 81,5%W =^ Ch(?n D ' '
Cau 168 M o t con lac d o n g o m vat c6 k h o i i u a n g m , d a y treo c6 chieu doi
1 = I m Keo con lie lech k h o i p h u o n g thang d u n g m o t goc ao = 0,1 (rad) mi
b u o n g k h o n g v a n toe ban d a u C o n lac c h i u l y c can m o i t r u o n g d g I a n coi nhu
k h o n g d o i va c6 gia t r i bang 0 , 1 % t r o n g l u g n g ciia vat Q u a n g d u o n g m a con
lie dao d p n g ke t u luc b u o n g tay cho den luc d u n g han la
Huong dan gidi:
Ap d u n g djnh luat bao toan va chuyen hoa nang l u p n g ta c6:
C a u 169: M o t con lac 16 xo c6 k h o i l u a n g vat nho la m j = 300g dao d p n g dieu
hoa v o i c h u k i I s Ne'u thay vat n h o c6 k h o i l u p n g m b a n g v a t n h o c6 khoi
l u p n g m ' t h i con lac dao d p n g v a i chu k i 0,5s Gia t r i m2 bang
A l O O g B 150g C 2 5 g D 75 g
Huang dan gidi:
Ta c6: = 0,5Ti => 2 7 c ^ | ^ = 0,5.27i =^ m ' = ^ = 75gam C h p n D
C a u 1 7 0 : M o t v a t n h o dao d p n g d i e u hoa v o l b i e n d p 4 c m v a c h u k i 2s
Q^aJTl: M p t con lac d o n c6 chieu d a i 121cm, dao d p n g d i e u hoa tai n o i c6 gia
toe t r o n g t r u a n g g L a y Tt'^ = 10 C h u k i dao d p n g cua eon lac la: , „ ,
A I s B 0,5s C 2,2s D 2s
Huong dan gidi:
Chu k i dao d p n g cua eon lac T = 2nJ- = 2nP^ = 2.1,1 = 2,2s
Vg V 7t2
=> C h p n C
Cau 172: M p t v a t n h o k h o i l u p n g lOOg dao d p n g d i e u hoa v o i chu k i 0,2 s va ca
nang la 0,18 J (moc the nang tai v j t r i can bang); lay =10 T a i l i d p 372 cm,
A 0,083s B 0,125s C 0,104s D 0,167s
Huong dan gidi:
Ta CO tai v j t r i l a i = 0 , 5 amax t h i 1x1= 0,5.A K h o a n g t h o i g i a n ngan nhat t i r
X = A d e n X = 0,5.A la t = T/6 = 0,5/6 = 1/12 = 0,083 ^ C h p n A
£ | u 174: H a i dao d p n g deu hoa e i i n g p h u o n g , c u n g tan so' c6 b i e n d p Ian l u g t
'a A i = 8cm, A2 =15em va l^eh pha nhau ^ Dao dpng tong h p p cua hai dao
•^Png nay eo b i e n d p b a n g
A 7 e m B 11 em C 1 7 e m D 23 em
Huang dan gidi:
H a i dao d p n g v u o n g pha nen b i e n d p dao d p n g t o n g h p p :
Trang 7A = 7 A I + A | =17cm
= > C h o n C - ' '
Cau 175: H a i con lac d o n c6 chieu dai Ian l u g t la 81 cm va 64 cm dugc tree Q
tran m o t can phong K h i cac vat nho ciia hai con lac dang 6 v i t r i can bang
dong thoi truyen cho chiing cac van toe cung h u a n g sao cho hai con l i e dao
dong dieu hoa v o i ciing bien do goc, trong hai mat phang song song v d i nhau
Gpi At la khoang t h o i gian ngan nha't ke t u liic truyen van toe den liic hai day
treo song song nhau Gia t r i At gan gia t n nao nha't sau day? >.„
A 8,12s B 2,36s C 7,20s D 0,45s
Huang dan gidi:
a),t —
^ 2
PT dao d p n g xi, X 2 : xi = A cos
H a i day song song nhau k h i xi = X2 hay cos
; X2 = A cos
7t (0,t
Cau 176 : M o t vat nho dao dong dieu hoa theo m o t q u y dao thang dai 12 cm
Dao dong nay c6 bien do la
A 3 cm B 24 em C 6 em D 12 cm
Huang dan gidi:
Bien dp = chieu dai q u y dao/2 = 12/2 = 6cm => Chpn C
Cau 177 : M o t vat nho dao dong dieu hoa doc theo true O x v o i bien d p 5 em,
chu k i 2 s Tai thoi diem t = 0, vat di qua can bSng O theo chieu d u a n g Phuong
t r i n h dao d o n g eua vat la
K h i t = 0 vat d i qua can bang O theo chieu d u o n g : x = 0 va v > 0
=> eoscp = 0 va sintp < 0 (p = -nil
P h u o n g t r i n h dao dong la x = 5eos
2) (cm) => C h p n A
end Dt 3
S O N G C O L
J HE T H O N G H O A K I E N THL/C
I Song CO hpc va cac dac t r u n g ciia song r , , ,
^) Dinh nghta song ca hoc
Song C O hpc la cac dao dpng dan hoi dupe Ian truyen d i trong moi trtfong vat chat theo thoi gian ;> t m t ' f '
- K h i song t r u y e n trong m p t m o i t r u o n g t h i cac phan t u ciia m o i t r u o n g chi dao dpng quanh v i t r i can bang ciia chiing ma k h o n g chuyen d o i theo song, chi CO pha dao dpng eua chiing dupe truyen d i ^
- Song CO hpc khong truyen dupe trong ehan khong .\nrn'<imn}A'-l
If) Phan loai song ca hpc
G o m hai loai la song ngang va song dpc
- Song ngang: la song c6 p h u o n g dao dpng eua eae phan t u m o i t r u o n g vuong goc v o i p h u o n g truyen song Song ngang t r u y e n dupe tren be mat chat long va trong chat ran V i d u : song tren mat nuoc,
- Song dpc: l a song eo p h u o n g dao dpng ciia cac phan t u m o i t r u o n g triing
voi p h u o n g t r u y e n song Song dpc truyen dupe trong chat ran, chat long va chat khi V i d u : song nen dan dpc theo mpt 16 xo
c) Cac dai luang dac trung cua song ca hoc
- C h u k i T cua song la chu k i dao dpng ehung eiia cac phan t u vat chat k h i
CO song truyen qua va bang chu k i dao dpng ciia nguon song
- Tan so f ciia song la tan so dao d p n g chung cua cac phan tCr vat chat k h i
CO song truyen qua ^ = ~
- Bien d p song a tai m p t diem la bien dp dao d p n g ciia phan t u vat chat tai
diem do k h i song truyen qua Thong t h u o n g cang ra xa t a m tao song t h i bien
<tpeangbe ;j'.)<fr
- Van toe t r u y e n song v la van toe truyen pha dao dpng (khac v o i v%n toe
Ciia cac phan t u dao dpng) N o la quang d u o n g song truyen d i dupe trong m p t don vj thoi gian Trong mpt m o i t r u o n g xae djnh, v bang hang so'
- Buoe song A l a khoang each giiia hai diem gan nhau nha't tren cung m p t
p h u o n g truyen song dao dpng cung pha Buoe song eQng la quang d u o n g ma Song truyen dupe t r o n g m p t chu k i ' '
Cong thiic lien h ^ T, f, v A: > = v.T = j ; T = j ; { = v = A f =
Trang 8N a n g lu ong song: Qua trinh truyen song la qua t r i n h truyen nang luong
Nang l u o n g cua song tai m p t v i t r i chinh la nang l u g n g cua cac phan t u
chat dao d p n g tai do va nang l u o n g cua song ty le thuan v o i b i n h p h u o n g hi^^
dp dao dpng
D o i v o i song phSng nang l u o n g song giam ty le v o i khoAng each D o i voj
song cau nang l u o n g giam ty le v o i b i n h p h u o n g ban k i n h Song phang ne'u b6
qua mat mat t h i bien dp dupe xem la khong d o i nen nang l u p n g t r u y e n qug
mpi diem la n h u nhau
2 P h u o n g t r i n h s o n g s
- P h u o n g t r i n h song la bieu thuc cho phep xac d i n h l i d p u ciia t i m g phan
t u X theo t h o i gian t
- Gia su p h u o n g t r i n h song tai O c6 dang: U Q = a.cos(a)t)
- Phuong t r i n h song tai M each O mot doan d (song truyen t u O den M):
aeoso) = acos (Ot- 2 7 1
-P h u o n g t r i n h song tai M ' each O mpt doan d ' (song t r u y e n t u M ' den O):
Uf^. = a cos CO = acos a)t + 27t—
- D p l^ch pha dao dpng giira hai diem M va N bat k i trong m o i truong
truyen song each nguon O Ian lupt la dM va dw: Acp = 27i = 27t M N
+ H a i d a o d p n g c i m g pha: A(]) = k 2 n (voi k e Z)
+ H a i d a o d p n g n g u p c pha: A(|) = (2k + 1).TT (voi k € Z)
+ H a i dao d p n g v u o n g pha: Acjj = (2k + 1) ^ (voi k e Z)
- P h u o n g trinh tren cho thay song c6 tinh tuan h o a n theo thoi g i a n va theo
k h o n g gian
+ T i n h chat tuan h o a n theo thoi gian eiia song: m p i d i e m tren d u o n g
t r u y e n c u a s o n g d e u dao d p n g tuan h o a n theo thai gian v o i c h u k i T V i du,
— t 2 7 l
-T X
diem P CO tpa d p d se c6 l i dp bien thien theo p h u o n g t r i n h Up =aeos
+ T i n h chat tuan hoan theo khong gian ciia song: tren toan m i e n truyen
song, l i dp u bien thien tuan hoan theo tpa dp, xet tai t h o i d i e m to ta c6
x,t = aeos ^27t 2 K ^
— tn - — X
^ G i a o thoa s o n g
\ sokhdi nietn
^ Giao thoa song la su tong hop hai hay nhieu song ket hop trong k h o n g
an trong do c6 n h u n g cho bien dp song tong h p p dupe tang cuong hoac eo
^hiJnS '^'^^ '^^ ^^"^ ^'^"^
Hai nguon ket h p p la hai nguon eo eung tan so va c6 d p Ipch pha k h o n g thay doi theo thai gian
Hai song ket h p p la hai song do hai nguon ket h p p phat ra l '
J,) phuong trinh song tong hop tai M f t, ,
* Tncong hop hai nguon CO do lech pha bat ky v
p h u o n g t r i n h song tai hai nguon eung p h u o n g Si, S2 c6 dang:
= acos(cot + c})i) va U2 = aeos(a)t + c|)2) ' ' '
Phuong t r i n h song tai M do hai nguon truyen toi:
" i M = aeos COt + CP] - 2 7 r d i '
va u 2M = aeos C0t + (p2 ~
27rd2^
Phuong t r i n h song tong hpp tai M :
= " i M + " 2 M =2acos d 2 - d i Acp cos
Bien dp dao d p n g tai M : A,^ = 2a cos d - i - d i Acp
X 2
v o i Acp = cp2 - cpi
Tren doan thSng noi \\x Si den S2 (S1S2 = 1) so cue dai, cue tieu giao thoa d i
qua chinh la so gia t r i k nguyen thoa man:
1 Acp , 1 Acp
— + — < k < —+ 1 In X 2n
1 1 Acp , 1 1 Acp + - X < k < + •
( k e Z )
( k e Z )
X 2' 2n " X 2 2n
* Truong hop hai nguon eung pha
Phuong t r i n h song tai hai nguon ciing p h u o n g Si, S2 eo dang:
Uj =acos(cot) va U 2 = aeos (cot)
- Phuong t r i n h song tong h p p tai M :
d 2 + d i
U M = U I M + L I 2 M = 2a cos d 2 - d i cos c o t 7 1 Bien dp dao d p n g tai M : Aj^^ = 2a cos 71 d 2 - d i
Trang 9-Tren doan thang noi tir S i den S2 (S1S2 = 1) so'eye dai, cue tieu giao tho,
qua ehinh la so'gia trj k nguyen thoa man:
+ So'cuc dai: - — < k < — (k e Z ) ;
• • X X
+ So cue tieu: - — - — <k< — -— ( k e Z )
* Trucmg hap hai nguon ngugc pha
- D o lech pha Acp = (2k + 1 )7T
P h u o n g t r i n h song tong hop tai M :
d , - d , 71
n—^— +
-X 2
" M = U i M + " 2 M = 2 a c o s cos
Bien do dao dong tai M : = 2a cos ^ d , - d i 7t^ n— - + —
Tren doan thang noi t u S i den S2 (S1S2 = 1) so eye dai, eye tieu giao thoa di
qua c h i n h la so'gia trj k nguyen thoa man:
Tren doan thSng noi t u S i den S2 (S1S2 = 1) so eye dai, eye tieu giao thoa t^'
qua chinh la so'gia trj k nguyen thoa man:
- Tgp h o p cac cue dai va eye tieu giao thoa la eac ho d u o n g hypebol fi'i"^^
xen ke nhau Ne'u hai n g u o n dao dpng cung pha t h i d u o n g t r u n g t r y c eiia 51-^'
1 7 A
• rnpt eye dai giao thoa; ne'u hai nguon dao dpng nguoc pha t h i d u o n g trung trifC la r " 9 t eye tieu giao thoa
T r o n g doan n o l giua hai n g u o n S1S2 khoang each g i i i a eac van eye dai
hoac eye tieu lien tie'p bang n h a u va bang ^ ; Khoang each g i i i a v a n eye d ^ va
(.yc tieu lien ke tren S1S2 la - • ,
4 S o n g d i m g
^) Mot sokhdi ni^m
Song CO cae n i i t song va b u n g song c6' d i n h t r o n g k h o n g gian gpi la
song d u n g
- Song d u n g la t r u o n g h o p dac biet eua giao thoa song: D o la sy giao thoa giua song t o i va song phan xa ciia no tren cung mot p h u o n g t r u y e n song
\)) Phuang trinh song tai mot diem M bat ky
- Xet doan day A B = 1, dau B co d i n h dau A dao d p n g v o i p h u a n g trinh:
- Bien dp dao d p n g tai M : A j ^ = 2a
+ M dao d p n g v o i bien dp eye dai hang AMm« = 2a (bung song) k h i
d = (2k + l ) ^ ; k e ' Z
+ M dao d p n g v o i bien dp eye tieu bSng AMmin = 0 (nut) k h i d = k ^ ; k 6 Z
c) Dieu ki^t deed song ditng tren day
- Day dai 1 co d j n h hai dau: 1 = k ^ (Chieu d a i cua day bang m p t so' nguyen Ian nira buoc song)
+ So b u n g : k / + S o n u t : k + l '* + So'bo song: k
+ Q u a n h ^ g i i r a k v a i f : l = k — = k - ^ = > - ^ = -^
2 2r 1^2 n ' <
+ Buoc song dai nhat Amax = 21 k h i k = 1 (chi co 1 bo song)
177
Trang 10- Day dai /co d i n h rriQt dau, mpt dau t y do: I = (2k +1)— (Chieu dai ,1
day bang mot so' le Ian mpt phan t u buoc song)
+ S o b u n g : k + l
f'j^L-+ S6'nut:k f'j^L-+ 1
d) Do van toe truyeh song
- D u n g hien tupng song dung, tit thi nghiem, ta do dup-c buoc song >
bang each do dupe X/2 khoang each giua hai nut song lien tie'p hoac hai byng
song lien tie'p va do dupe tan so' f
- D u n g eong thuc v = Xf ta t i m dupe van toe v
5 Song am
a) Song dm
- Song am la song co hpc ma tai con nguoi c6 the cam nhan dupe Song am
CO tan so nam trong khoang t u 16Hz den 20.000Hz N g u o n am la ba't k i vat nao
phat ra song am
- Cac am co tan so tren 20 OOOHz gpi la sieu am (tai d o i cam thu dupe)
- Cac am co tan s o d u o i 16 H z gpi la ha am (tai cho cam thu dugfc)
b) M6i trubng truyen dm vd van toe truyen dm
- Song am truyen dupe trong cac moi truong vat cha't dan hoi n h u ran,
long, k h i Song am khong truyen dupe trong ehan khong N h i r n g vat l i ^ u nhu
bong, nhung, nhirng tarn xo'p truyen am kem, ehiing dupe d u n g de lam vot
l i f u each am
' - Van to'e truyen am phu thupc vao tinh dan hoi, mat dp va nhiet dp cua
moi truong Van toe truyen am trong chat ran Ian hon van to'e truyen am trong
chat long, van toe truyen am trong chat long Ion hon van toe truyen am trong
chat k h i
- Song am truyen trong chat k h i la song dpc; song am truyen trong chat
ran bao gom ca song dpc va i o n g ngang
c) Cac dac tntng vdt ly cua dm thanh
- Tan so am: f t u l 6 H z d e ' n 20.000Hz
- Cuong dp am va muc cuong dp am:
+ C u o n g dp am I tai mpt diem la nang l u p n g truyen trong m p t don v!
thoi gian qua mpt don vj d i ^ n tich dat vuong goe voi p h u o n g truyen am to'
E E P
diem do I = — = — D o n v j : W/m^ (oat tren met vuong)
S-t 47tR^t 47iR^
+ M u c cuong dp am L la dai lupng do bang loga thap phan cua ty s^'
giiia cuong dp am I tai diem dang xet va cuong dp am chuan lo (lo = 10"^^ W/m
ung v o i tan so' f = 1 OOOHz)
Neu d u n g d o n v j la Ben (B) thi: L = l o g : ^
Neu d u n g d o n v i la dexiben (dB) thi: L = l O l o g —
IQ ^ p
^) Cac dac trtmg sinh U cua dm thanh
D p cao: La dac t r u n g sinh l i eua am, phu thupc vao tan so' am A m cao (tharih) la am co tan so' am Ion; am thap (tram) la am eo tan so' am nho D p thap
|,ay cao ciia am con dupe hieu qua su tram hay bong cua am
- Dp to: La mpt dac t r u n g sinh l i ciia am, p h y thupc vao m i i c cuong dp am
- A m sac: La mpt dac t r u n g sinh l i ciia am, phu thupc vao tan so' am, bien
dp song am va cac thanh phan ca'u tao eiia am, tiic la p h u thupc vao do thi dao dpng cua am
+ A m CO ban va hoa am: M p t nhac cu phat ra mpt am co tan so fo (am co
ban hay hoa am t h u nha't) thi bao gio cung phat ra dong thoi cac hoa am thii 2,
3, CO tan s6'2fo, 3fo, Do hien tupng do, am phat ra t u mpt nhac cu la su tong hpp cua am co ban va cac hoa am, no dupe gpi la nhac am, tuy no co tan so'cua
im CO ban fo n h u n g d u o n g bieu dien cua no khong eon d u o n g h i n h sin dieu hoa ma la mpt d u o n g cong tuan hoan phue tap co chu k i , ta gpi no la do thj dao dpng cua am Hpa am nao co bien dp Ion nha't se quyet d j n h dp cao cua am phat ra
+ Dao dpng am tong hpp co tinh tuan hoan, dang cang phue tap thi so
hpa am cang nhieu, am sac cang phong phii Cimg mpt am sol do nhieu dung
^ khae nhau phat ra sac thai am thanh ma ta nghe khac nhau la do so' hpa am toan khac nhau
+ A m dupe phat ra t u mpt tieng no, tieng go vao tam k i m loai, gpi la
am, chving khong co tan so' xae djnh, do thi cua ehung la d u o n g cong ' ^ o n g tuan hoan
^guon nhac dm vd hgp cong huong
- N g u o n nhac am la nhirng nguon phat ra nhac am, tuc la phat ra nhung
^ CO tan so xae djnh, moi nhac cu la mpt nguon nhac am
- H o p cong h u o n g la mpt vat rong co kha nang epng h u o n g doi v o i nhieu
so khac nhau v tang cuong nhirng am co cac tan so do
Trang 11II C A C D A N G B A I T A P V A V I D y MINH HQA
Dong^: X A C D I N H C A C D A C T R l / N G CUA S O N G C O H Q C
* Phuong phap giai: - Su dung cac cong thuc: to = 27tf = ^ = v T =
V i 1: M o t nguoi quan sat mpt chiec phao tren mat bien thay no nho cao
len 6 Ian trong 10 giay va thay khoang each giiia hai ngpn song ke nhau la
0,2m Van toe truyen song bien bang:
A 12cm/s B lOcm/s C 24cm/s D 20cm/s
Huong dan giai:
Khoang thoi gian giiia 6 Ian nho lien tiep la 5 chu ki => 5T = 10 => T = 2s
Khoang each 2 ngpn song ke nhau la 0,2m => A = 0,2m = 20cm
n A, 20
• Van toe truyen song la: ^ ^ ^ ^ ^ 10cm / s
^ z ^ C h p n B
Lira y:
- O day hoc sinh c6 the nham nhu sau:
+ Khoang thoi gian giOa 6 Ian nho lien tiep la 6 chu ki => 6T = 10 => T = 5/3s
"k 20
Van toe truyen song la: v = — = — = 12cm / s => ehpn A
3
+ Khoang each 2 ngpn song ke nhau la 0,2m => A = 0,4m = 40cm
" -> Van toe truyen song la: ^ = ^ = ^ IQcm / s => ehpn D
+ Khoang thoi gian giCra 6 Ian nho lien tiep la 6 chu ki => 6T = 10 => T = 5/3s
Khoang each 2 ngpn song ke nhau la 0,2m A = 0,4m = 40cm
Van toe truyen song la: v = — = ^ = 24cm / s => ehpn C
3
V i d u 2: M p t nguoi quan sat song tren mat ho thay khoang each giua hm
ngpn song lien tiep la 0,5m va c6 10 ngpn song di qua truoc mat trong 9^
Van toe truyen song tren mat nuoe bang:
A 55,56cm/s B lOOcm/s C l l l , l l c m / s D 50em/s
Huong dan giai:
Khoang each 2 ngpn song ke nhau la 0,5m nen A = 0,5m = 50cm
Co 10 ngpn song di qua truoc mat trong 9s nen chu k i song la:
O day hoe sinh c6 the nham mpt trong cac truong hpp n h u sau:
+ Khoang each 2 ngpn song ke nhau la 0,5m nen A = I m = 100cm Van toe truyen song la: v = ^ = = lOOem / s => chpn B
+ Co 10 ngpn song di qua truoc mat trong 9s nen chu k i song la: lOT = 9s
^ T = 0,9s
=>Van toe truyen song la: v = ^ = = 55,56cm / s => chpn A + Khoang each 2 ngpn song ke nhau la 0,5m nen A = I m = 100cm
Co 10 ngpn song di qua truoc mat trong 9s nen chu k i song la: lOT = 9s
=> T = 0,9s Khi do van toe truyen song la: v = — = - — = 111,11cm / s
T 0,9
=> chpn C
Dang 2: B A I TAP V E P H l / O N G T R I N H SONG V A D O L E C H PHA
G I 0 A HAI D I E M T R E N PHLfONG T R U Y E N S O N G
* Phuong phap giai ^
- Gia su phuong trinh song tai O c6 dang: Uy = a.cos(a)t)
- Phuong trinh song tai M each O mpt doan d (song truyen tir O den M ) :
u ^ = acosco
- Phuong trinh song tai M each O mpt doan d (song truyen tit M den O):
t — = aeos cot 2 7 1
-( d^
acosco t + - = aeos COt +
27t Dp lech pha dao dpng giira hai diem M va N bat ki trong moi truong
t''uyen song each nguon O Ian lupt la dM va dw: Acp =
27t-+ Hai dao dpng cung pha: Acp = k27T (k e Z)
+ Hai dao dpng ngupe pha: Acp = (2k + 1 ).TT (k € Z)
+ Hai dao dpng vuong pha: Acp = (2k + 1) ^ (k e Z)
Trang 12* Cdc vi du tninh hpa:
V i d^ 1: Song t r u y e n tai m a t chat long v o i buac song 0,1m P h u a n g trhih
dao d o n g tai n g u o n O c6 dang UQ = Scoscot (mm) P h u o n g t r i n h dao d p n g tai
d i e m M each n g u o n O m p t doan 6cm theo p h u a n g t r u y e n song la:
A u ^ = 5cos(cjt + l,27t ) ( m m ) B u , ^ = 5cos(cot + 1207i ) ( m m )
C U [ ^ = 5cos(a)t - 1207T) ( m m ) D u ^ = 5cos(ajt - l,2n) ( m m )
Huong dan gidi:
P h u a n g t r i n h song tai M d o O truyen den c6 dang:
u ^ = 5 cos ( 2nd' cot = 5 cos = 5 cos cot 271.6^
P h u o n g t r i n h song tai M do O truyen den c6 dang:
U j ^ =5cos| cot + 2nd = 5 cos cot + 27C.6
10
=> chpn A
+ N h a m ve d o n v i chua d o i thong nhat:
P h u a n g t r i n h song tai M d o O truyen den c6 dang:
V i d\ 2: N g u o n song co truyen theo m o t d u a n g thang, n g u o n dao d p n g v o i
p h u a n g t r i n h UQ = acoscjt (cm) M p t d i e m M tren p h u a n g t r u y e n song each
n g u o n d = A/3 tai t h o i d i e m t = T/2 c6 l i d p = 2cm C o i bien d p song
k h o n g b j suy giam, bien dp song a la:
A 2cm B 4em C 2 x / 2 e m D 4 V 2 c m
Huong dan gidi:
P h u a n g t r i n h song t?ii M c6 dang: U j ^ = a cos cot 27cd (cm)
Thay U j ^ = 2cm, t = T/2 va d = A/3 vao p h u a n g t r i n h tren ta dugic:
2 = acos
T 2 3.x => 2 = acos ( r t - — ) = — =>a = 4cm => C h p n B 3 2
V i d u 3: M o t song co hpc ca bien d o a, buoc song A Biet v a n toe dao d g n g eye d a i eiia p h a n ttr m o i t r u o n g bang 2 Ian toe d p t r u y e n song, bieu thiic diing la:
A A = Tia B X = 27ia C A = 2na/3 D A, = 37ia/2
Huong dan gidi:
In
.a
j ^ ^ y J ^ Vddmax J ^ ^ T ^ J _ T = na ^ C h o n A
^ 2 2 2
V i d u 4: N g u o n song co t r u y e n tren m p t spi day d u a c m o ta b a i p h u o n g
trinh u = acos(27rt - 0 , l 7 t x ) , t r o n g d o u va x dupe d o bang cm, t d o bang s Tai m o t t h o i d i e m da cho d p lech pha dao d p n g ciia h a i p h a n t u tren day each n h a u 2,5 c m la
A ^ B ^
Huang dan gidi:
- P h u a n g t r i n h song tai m o t d i e m M co dang: u = a cos
- Theo gia thiet u = a cos (27it - 0, ITIX)
cot 27tX
nen u = a c o s ( 2 7 i t - 0 , l 7 t x ) = acos cot 27rx 0,l7ix = — ^ A = 20em
D p l$eh pha dao d p n g ciia hai phan t u tren day each n h a u 2,5 c m la:
2iid 27t.2,5 7t,
Acp = ^
C h p n D
20 4^ ^
V i d u 5: M o t song t r u y e n tren m a t nuoe bien co buac song X = 2 m Khoang
each giira hai d i e m gan nhau nhat tren cimg m p t p h u a n g t r u y e n song dao
<lpng ngupc pha nhau la:
A 1,25 m B 2 , 5 m C 5 m D 1 m
Trang 13Huong dan gidi:
Khoang each giua hai diem gan nhau nhat tren ciing mpt phuong truy^Y,
song dao dpng ngupe pha nhau la: d = X/2 = 1 m => Chpn D
V i dv 6: Mpt song truyen tren mat nuoc bien c6 buoc song X = 2m Khoang
each giiia hai diem gan nhau nhat tren cung mpt phuong truyen song dao
dong l^ch pha nhau n/2 la:
A 0,75 m B 3 m
C 0,5 m D Mpt gia tri khac
Huomg dan gidi:
Dp l?ch pha dao dpng ciia hai phan tu tren phuong truyen song each nhau
V i du 7: Song truyen tren day voi van toe 4 m/s c6 tan so' song thay doi tu 2 2
Hz den 26 H z Diem M each nguon mpt doan 28 cm luon dao dpng vuong
pha voi nguon Buoc song truyen tren day la:
A 160 em B 1,6 cm C 16em D 100 cm
Huong dan gidi:
D p l^ch pha dao d p n g ciia hai phan tu tren phuong truyen song each nhau
* Phuang phap giai:
Phuong trinh song tong hop tai diem M:
Phuong trinh song tai hai nguon cung phuong Si, S2 c6 dang:
U j = aeos(cut + cpi) va U j = acos(a)t + 92)
phuong trinh song tai M do hai nguon truyen tai:
MM = acos cot + (pj - 27id, ^ va U j M =aeos cot + - 27td2^
phuong trinh song tong hpp tai M:
1 Acp , 1 Acp /, „^
— + — < k < —+ — ( k e Z j
; i 27t X In
1 1 Acp , 1 1 Acp /, + — < k < + — ( k e Z )
- Khi giai bai toan giao thoa, can kiem tra dp l§ch pha eua hai nguon
- Khi hai nguon dao dpng voi bien dp khac nhau thi phuong trinh song tong hop tai M bat ky dupe xae djnh nhu tong hpp hai dao dpng (hai dao dpng
*hanh phan la hai song do hai nguon truyen den M) va bien dp dao dpng tai M
Trang 14duQC ti'nh: = yja^ +al+ la^aj cos(A(p) trong do A(p la dp l^ch pha ciia haj
song thanh phan tai M
- V o i bai toan t i m so d u a n g dao dpng voi bien do cue dai, cue tieu giijg
hai diem M , N bat ky each hai nguon Ian lugt la d j ^ , 62^, d j ^ j , d j ^ thi lam
nhu sau:
+ Dat A d ^ j = d 2 M - d , M ; ^ d N = d 2 N - d i N ; Gia su Ad^^ > Ad^j
! + N e u hai nguon dao dong eung p h a :
* Cue d a i : A d ^ < k > i < A d M
* ' * Cue tieu: Ad^J < ( k + 0 , 5 ) ? L < A d M *
+ Neu hai nguon dao dpng nguge p h a :
* C y c d a i : Adf^ < ( k + 0 , 5 ) > i < A d | ^
* Cue tieu: Ad^j < k A < A d ^
Sogia t r i nguyen ciia k thoa man cac bieu thue tren la so d u a n g can tim
* Cdc vi du mirth hoa:
V i d v 1: Trong thi nghiem ve hi^n tugng giao thoa song, n g u o i ta tao tren
mat nuoc hai nguon A va B dao dong cung phuong trinh: u ^ = 5cosl07tt
(cm) va U g = 5cos(107rt + 71) (cm), van toe truyen song tren mat nude la
20cm/s D i e m M tren mat nuoc c6 M A = 7,2 cm, M B = 8,2 cm c6 phuong
trinh dao dong la :
A u ^ =5N/2cos(207tt-7,77t)cm B u ^ =5>^cos(l07tt + 3,35ji)cm
C U[^ =10V2cos(l07it-3,357i)cm D u^^ =5N/2cos(l07tt-3,357t)cm
Huang dan gidi:
- Buoc song A = v/f = 20/5 = 4 (cm)
- Phuong trinh song tong hgp tai M :
" M = " i M + U 2 M = 2 a c o s cos (ot-n— - + — ~ d j + d j (pi+92
u^^ =2.5 cos 8 , 2 - 7 , 2 cos
4 2 = 5V2cos(l07tt-3,357t) r:> Chpn D
y f d y 2: Trong mpt thi nghiem giao thoa song tren mat nuoc, hai nguon ket
Pi^p S i va S2 dao dong voi tan so' 16 Hz, cung pha Tai diem M each hai
pguon Ian lugt la d i = 30 cm va d2 = 25,5 em, song eo bien dg cue dai Giiia
va d u o n g trung true ciia S1S2 c6 them mot ggn loi nua Van toe truyen
song tren mat nuoc la A^24 em/s B 36 cm/s C 72 m/s D 7,1 cm/s
Huang dan gidi:
H a i nguon dao dong cung pha, tai M song co bien dp eye d ^ i nen
^ , , d 2 = k.A
„^:^P Giiia M va d u o n g trung true ciia S1S2 c6 them mgt ggn loi nua nen k = 2„^:^P
V?y 30 - 25,5 = 2.A Buoc song A = 2,25 cm
=> Van toe truyen song tren mat nuoc la v = A.f = 2,25.16 = 36 (em/s) => Chgn B Luu y: Co the nham n h u sau
- k = 3 Vay 30 - 25,5 = 3.A;
Buoc song A = 1,5 em ^ v = A.f = 1,5.16 = 24 (cm/s) =>Chgn A
Vi 3: O be mat mgt chat long c6 hai nguon phat song ket hgp S i va S2 each nhau 20cm Hai nguon nay dao dgng theo phuong thSng dung c6
phuong trinh Ian lugt la u^ = 5eos (407tt + n/6) (mm) va U j = 5cos(407tt + 77t/6)
(mm) Toe do truyen song tren mat chat long la 80 cm/s So diem dao dgng voi bien do cue dai tren doan th^ng S1S2 la
Trang 15S S 1 S S 1
So cvrc tieu giao thoa tren S1S2 — L i _ - < k < - - -> - I K k < 10
V i k e Z n e n k = -10,-9, ,9
Co 20 gia trj ciia k, vay c6 20 diem tren doan S1S2 khong dao dpng -> chpn D
V i dv 5: Tai hai d i e m A va B tren mat nuoc c6 2 n g u o n song dao d o n g cung
pha, bien dp Ian l u p t la 4cm va 2cm, buoc song la 10cm D i e m M tren mat
nuoc each A 25cm va each B 30cm se dao d p n g v o i bien dp la
A 2cm B 4cm C 6cm D 8cm
H a i n g u o n dao d p n g cung pha nen bien dp dao d p n g tai M :
= V ^ i + ^2 + ^^\^2 COS(A(P)
2 7 r ( d , - d , )
V o i Acp = — — — = n Suy ra A M = 2 cm ^ Chpn A
V i dy 6: H a i dau M va N ciia mpt mau day thep nho h i n h chi> U dupe dat
cham vao mat nuoc Cho mau day thep dao d p n g dieu hoa theo phuong
v u o n g goc v o i mat nuoc Bie't M N = 6,5cm dao dpng v o i tan so' f = 80Hz ; toe
dp t r u y e n song v = 32cm/s ; bien dp song khong d o i A = 0,5cm Ve m p t vong
tron Ion bao ca hai n g u o n song vao trong Tren vong tron ay c6 bao nhieu
d i e m CO bien dp dao d p n g cue dai
M N dao d p n g v a i bien dp cue dai K h i do vong tron bao q u a n h hai nguon
va N cat cac van cue dai 6 66 diem => Chpn D
Dang 4: BAI TAP VE SONG Dl/NG
* Phuong phdp:
Phuong trinh song tai mot diem M bat ky:
- Xet doan day A B = 1, dau B co d i n h dau A dao d p n g v o i p h u o n g trinh:
Dieu kien deed song ditng tren day
Day co'djnh hai dau: 1 = k ^ + So'byng: k
+ So'nut: k + 1 + So'bo song: k
A ,
+ Q u a n h# giira k v o i f: 1 = k — = k —
+ Buoc song dai nha't Amnx = 21 khi k = 1 (chi co 1 bo song)
- Day CO d j n h m p t dau, mpt dau t u do: 1 = (2k + 1 ) ^ + S 6 ' b u n g : k + 1
+ S o n u t : k + l
Luu y:
- Khoang each giiia 2 nut song hay hai bung song bat ky: d - k - ^ , k = 1,2,3
- Khoang each giOa 1 niit song v o i 1 b u n g song bat ky:
d - ( 2 k + l ) ^ , k = 0,1,2,3 ^,
- T h o i gian hai Ian day d u o i thSng lien tie'p: At = • •[ A
Be rpng cua m p t b u n g song la: 4a
M p t spi day thep cang th^ng, dat gan m p t dau n a m cham dien thang, dong dien qua n a m cham co tan so'f thi day se dao d p n g v o i tan so 2f
- M p t spi day no'i v o i nguon d i f n xoay chieu tan so f, day dat trong khoang giira hai ban cua m p t n a m cham h i n h chCr U t h i day se dao d p n g v o i tan so cung la f
y
- Tan so do day dan phat ra (hai dau day c o d i n h ) : f = k — ; k e N
- Tan so do 6'ng sao phat ra (mpt dau bjt k i n , m p t dau de h o m p t dau la
^ut song, m p t dau la b u n g song): f = (2k + 1 ) - ^ ; k e N
Trang 16iv> inuuigmi ruiunn B I I I \ L I LJ., lup i - i \ g u y e n jjuang i.ac
Cdc vi du minh hga:
Huang dan gidi:
Dieu kien de c6 song dirng tren day trong truong hop hai dau co'djnh:
Vi d u 2 : Mot day dan c6 chieu dai 90cm, khi gay phat ra am co ban tvrong
ung CO tan so f Muo'n cho day nay phat ra am co ban f = l,2f thi phai b a n i
phim cho day ngan lai con chieu dai 1' bang
A 60 cm B 75cm C 50cm D 65cm
Huang dan gidi:
Dieu kien de co song dung tren day trong truong hop hai dau co d i n h
I = n ^ A m CO ban do day dan phat ra ling voi n = 1 => 1 = ^ = ^ (*) i
Tuong tu de co tan so' f thi ' ~ ^ ~ ^ (**)
T u H v a r ) s u y r a i-= 1 =:> j'= _ = _ = _ ^ _ = 75cm Chon B ^ ' ^ ' y I f f i,2f 1,2 1,2
Vi du 3: Song dung tren day AB co hai dau co dinh, chieu dai 40cm Tan so
dao dgng cua day la 50Hz, van toe truyen song tren day la 4m/s Tren day co:
A 10 bung, 11 nut B 10 bung, 10 niit
C 5 niit, 5 bung D 9 bung, 10 nut
Huang dan gidi:
irmn miv UVVH KHattg^rtfT
y i du 4: Nguoi ta t^o song dirng tren mot soi day cang ngang giira hai diem
CO djnh Song dung dugc tao ra tren day Ian lugt voi hai tan so' gan nhau jiha't la 200Hz va 300Hz Tan so' kich thi'ch nho nha't ma van tao ra song dung tren day la :
A lOOHz B 50Hz C 200Hz D 150Hz
Huang dan gidi:
- Dieu ki^n de co song dung tren day trong truong hgp hai dau co djnh:
2.200 2.300
V
tAy se CO 1 = 200 + Thay vao bieu thuc fmin ta dugc fmin = lOOHz -> Chgn A
Vi d u 5: Mot day AB hai dau co dinh Khi day rung vol tan so'f thi tren day
CO 4 bo song Khi tan so tang them 10 Hz thi tren day co 5 bo song, van toe truyen song tren day la 10 m/s Chieu dai va tan so rung cua day la:
A 1 = 50 cm, f = 40 Hz B / = 40 cm, f = 50 Hz
C./ = 5cm, f = 50Hz D / = 50 cm, f = 50 Hz
Huang dan gidi:
- Day AB hai dau co'djnh nen chieu dai cua day la • i
l = k ^ = k ^ = ^ f =
k.-^-2 k.-^-2f k.-^-21
- Khi day rung voi tan so f thi tren day co 4 bo song: f = 4 ^ (1)
- Khi tan so tang them 10 Hz thi tren day co 5 bo song: f +10 = 5.-^ (2)
Tu (1) va (2) suy ra ^ = 10 ^ 1 = 0,5m - 50cm JThay vao (1) suy ra f = 40 Hz =:> Chgn A
du 6; Mot sgi day M N treo lo lung, dau tren M gan vao am thoa dao dgng voi chu ki T = 0,02s, toe do Ian truyen song la 2m/s De tren day co
^ n g dung, voi 13 niit va 13 bung (ke ca hai dau), thi sgi day phai co chieu bang bao nhieu?
- _ A 20 cm B 30 cm C 50 cm D 25 cm
Trang 17Huang dan gidi:
- Cac bai toan thuong gap o dang nay la xac dinh cac dai lug-ng dac trung
cho song am n h u van toe am, muc cuong dp am, tan so am, tan so cac hoa
V i 1: M o t song am dupe phat ra t u mot nguon am c6 dang hinh cau Biet
tai diem each nguon 2m, cuong do am la 0,06W/m2 c i a su nang l u g n g phat
ra dupe bao toan Xac djnh cong suat phat am ciia nguon
A 5 W B 4 , 5 W C 4 W D 3 W
Huong dan gidi:
Nang l u p n g dupe phan bo deu tren dien tieh mat song la mat eau: S = 47:R
Cong suat phat am la: P IS = 0,06.4TT.2^ « 3 W -> Chpn D
V i du 2; M p t la thep mong, mpt dau eo djnh, dau eon lai dupe kich thich de
dao dpng v o i ehu ki khong doi va bang 0,08s A m do la thep phat ra la
A sieu am B ha am
C nhae am D am ma tai nguoi nghe dupe
Huang dan gidi:
1 = 12,5HZ
T
A m do la thep phat ra la ha am Chpn B
Tan so cua am phat ra la f = ^ = 12,5Hz
V i d u 3: M p t cai gieng sau 20m tinh t u thanh den mat nuac M p t em be dung gain thanh gieng, do so y da danh roi ehie'c bat Biet v | n toe truyen am trong khong k h i la 320m/s, lay g = lOm/s^ Tinh thoi gian t u liic danh roi den luc nghe thay tieng bat cham vao nuoc
A 2,4s B 2,1s C 2s " D 2,0625s
Huang dan gidi:
- Thoi gian t u khi ehie'c bat roi den khi cham vao m§t nuoc la
- Thoi gian t u liic bat cham vao mat nuoc den k h i nghe thay tieng bat
h 20 cham vao mat nuoc la t , = — = = 0,0625s
V 320
- Vay tong thoi gian la t = t j + t j = 2,0625s -> Chpn D
V i du 4: M p t nguoi dung biia go nh? vao d u o n g sat va each do 1376m, eo
mpt nguoi ap tai vao d u o n g sat thi nghe thay tieng go som hon 3,3s so voi tieng go nghe trong khong khi Van toe am trong khong k h i la 320m/s Van toe am trong sat la
A 1238m/s B 1356m/s C 1336m/s D 1376m/s
Huang dan gidi:
- Gpi t la thoi gian nguoi kia nghe dupe tieng go trong d u o n g sat ke t u flic go
* - V o i v J, V2 la van toe am truyen trong sat va trong khong k h i
Ta c6: V j t - V2 ( t + 3,3) = 1376 ^ t = Is ; v i = 1376m/s Chpn D
V i d^ 5: M p t nguoi d u n g gan 6 chan niii h i i len m p t tieng Sau 8s nghe tieng
minh vong lai, biet van toe am trong khong khi la 340m/s Khoang each t u chan niii den nguoi do la
_ A 1333m B 1386m C 1360m D 1320m
Huang dan gidi:
Gpi / la khoang each t u nguoi do den chan niii
Theo de ra vt 21 => 1 = y = 1360m => Chpn C
V i du 6: Hai am eo muc cuong dp am hon kem nha 40dB Ty so cuong dp 9ni cua chiing la:
_ A 400 B.100 C 40 D 10000
Trang 18Huang dan gidi:
V i dy 7: H a i hoa am lien tiep do mq>i day d a n phat ra c6 tan so h o n kem
nhau 56Hz Hoa a m t h i i 4 c6 tan so:
A 2 8 H Z B.224HZ C 86Hz D 168Hz
Huang dan gidi:
Theo bai ra: n f - (n - l ) f = 56 - » tan so am co ban f = 56Hz
Vay tan so hoa a m t h u t u f4 = 4f = 4.56 =224 Hz -> Chon B
Huang dan gidi:
Song ngang truyen dupe trong m o i t r u o n g ran va tren mat chat long
=> C h p n C 5 i
Cau 2: Song dpe dupe truyen trong m o i t r u o n g nao d u o i day:
A RSn, long, k h i B R^n, long
C K h i , chan k h o n g D R^n, chan k h o n g
Huang dan gidi:
Song dpe t r u y e n dupe trong cac m o i t r u o n g rin, long, k h i C h p n A
Cau 3: Ket luan nao sau day khong dung ve s u truyen song co
A Qua t r i n h truyen song k e m theo sy van chuyen vat chat theo p h u o n g
truyen song
B Qua t r i n h truyen song kem theo s u t r u y e n nang l u p n g t u n g u o n toi
n h i j n g cho trong m o i t r u o n g ma song t r u y e n t a i
C Q u a t r i n h truyen song la qua t r i n h truyen pha dao d p n g
D V^n to'c truyen song la van toe truyen pha dao dpng
194
' Huang dan gidi:
Cac dap an B, C, D deu d i i n g Chon A
Ket l u a n nao sau day khong diing ve s u truyen song co
A Song ngang la song m a p h u o n g dao d p n g ciia p h a n t u m o i t r u o n g
v u o n g goc v o i p h u o n g truyen song
B Song dpe la song ma p h u o n g dao d p n g ciia p h a n t u m o i t r u o n g t r u n g
v o i p h u a n g truyen song
C Song t r u y e n t r o n g m o i t r u o n g ran l u o n la song dpe
D Song t r u y e n t r o n g m o i t r u o n g k h i luon la song dpe
Huang dan gidi:
T r o n g m o i t r u o n g ran g o m ca song dpe va song ngang -> C h p n C
C g u S : V a n toe truyen song p h u thupe vao yeu to nao?
A N a n g l u p n g song B Tan so dao dpng
C M o i t r u o n g truyen song D Buoc song
Huang dan gidi:
Van toe t r u y e n song p h y thupc vao m o i t r u o n g truyen song ->Chpn C
Cau 6: M o t song co hpc co bien dp A, buoc song X Toe d p dao d p n g eye dai
ciia phan t u m o i t r u o n g bang 3 Ian toe dp truyen song T i m h ^ thue lien h?
giua A va X
A A = 2 T I A / 3 B A = 27XA C A = 37TA/4 D A = 3nA/2
Huang dan gidi:
T ' A o ^ -1 AcoT 27iA ^
Ta CO Acj = 3— =>X = => Chpn A
T 3 3
X a u 7: N g u o n phat song S tren mat nuoe tao dao dpng v o i tan so f = lOOHz gay
cac song t r o n Ian rpng tren mat nuoe Bie't khoang each giira 7 g p n l o i lien tiep la 3 cm Toe dp truyen song tren mat nude bang
A 25 cm/s B 50 cm/s. C 100 em/s D 150 em/s
Huang dan gidi:
Khoang each giCra 7 gpn loi lien tiep la 3 cm: 6A = 3 em => A = 0,5 c m Toe dp t r u y e n song tren mat nuoe bang v = A f = 0,5.100 = 50 cm/s
=> C h p n B
Cau 8: M o t d i e m O tren mat nuoe dao dpng v o i tan so 20 Hz, v g n toe truyen
Song tren mat nuoe thay d o i t u 0,8 m/s < v < Im/s Tren mat nuoe h a i d i e m A
Va B each nhau 10 c m tren p h u a n g truyen song l u o n dao d p n g ngupc pha ' A a u Buoc song tren mat nude la:
A 4 cm B 16 cm. C 25 cm D 5 cm .,•<• ,
Trang 191^1 inuttigminnuTiHBins varu ii, rapi-Nguym nuangLac
Huang dan gidi:
D p l§ch p h a d a o d p n g c u a h a i p h a n t u tren p h u o n g t r u y e n s o n g each nhai
d la: A(p = ^ | ^ ( r a d ) T h e o gia thiet
A 2 m/s B I m / s C 0,4m/s D M p t gia tri khac
Huong dan gidi:
A V a n toc B T a n so' C B u o c song D N a n g l u p n g
Huang dan gidi:
V a n toc t r u y e n s o n g trong cac m o i t r u o n g k h a c n h a u la k h a c n h a u ; d o vay
khi m p t s o n g c o t r u y e n t u m o i t r u o n g n a y s a n g m o i t r u o n g k h a c thi v a n toc
thay doi, b u o c s o n g v a n a n g l u p n g c u n g thay doi c h i co tan so la k h o n g thav
C a u 12: M p t s o n g c o h p c Ian t r u y e n trong m o i t r u o n g d a n h o i v o i v a n toc
k h o n g doi, k h i tang tan so len 3 Ian thi b u o c s o n g
B T a n so ciia s o n g c h i n h b 3 n g tan so dao d p n g ciia cac p h a n t u d a o d p n g
C Toe dp c u a s o n g c h i n h b a n g toc dp d a o d p n g c u a cac p h a n t u d a o dpng
D B u o c s o n g la q u a n g d u o n g s o n g t r u y e n d i d u p e trong m p t c h u k y
Huang dan gidi:
T r o n g cac d a i l u p n g d a c t r u n g c u a s o n g thi: C h u k y c i i a s o n g c h i n h b a n ? chu k y d a o d p n g c u a cac p h a n t u dao dpng; T a n so ciia s o n g c h i n h b a n g tan so dao d p n g c u a cac p h a n t u d a o dpng; C o n toe dp t r u y e n s o n g la toc d p t r u y e n pha dao d p n g v a k h o n g b a n g toc dp dao d p n g c u a cac p h a n t u d a o d p n g
C a u 14: M p t s o n g c o I a n t r u y e n tren m p t d u o n g t h a n g t u d i e m O d e n d i e m M
each O m p t d o a n d Biet tan so f, b u o c song X v a b i e n dp a c u a s o n g k h o n g doi
trong q u a t r i n h s o n g t r u y e n N e u p h u o n g t r i n h d a o d p n g c u a p h a n tit vat c tai d i e m M co d a n g U j ^ ( t ) = a sin27rft thi p h u o n g trinh d a o d p n g c u a p h a n ti'*-
V9t chat tai O la:
Huong dan gidi:
P h u o n g trinh d a o d p n g c u a p h a n t u vat chat tai O s o m p h a h o n tai M la
^oi t tinh b a n g giay T r o n g k h o a n g thoi gian 2s s o n g n a y t r u y e n d i d u p e q< ~ 7
^irong b^ng bao n h i e u Ian b u o c song?
A 10 B 40 C 30 D 2 0 ,
A-19/
Trang 20Huang dan gidi:
to
Tan so song la f = — = lOHz ; Van toe song la v = A.f = lOX
271 Quang dirong la S = v.t = 10X.2 = 20X Chpn D ci JW/fv
Cau 16: M p t n g u o i quan sat m p t chiec la tren mat nuoc thay no nho cao 8 JaY,
trong 14 giay Khoang caeh giua hai ngpn song lien tie'p la 2m Van to'c truyen
song la
A Im/s B 2m/s C 3m/s D 4m/s
-» Huang dan gidi:
Chiec la nho cao 8 Ian, tuc la thuc hi^n dupe 7 chu k i trong 14 giay
=> C h u k i dao dpng eiia chiec la la T = 2s;
Van to'c truyen song la v = A/T = 1 m/s => Chpn A
Cau 17: M p t song co hpe truyen trong m o i truang dan hoi v o i van toe 3m/s va
chu k i 0,5s Buoc song cua no la
A U j ^ = 4 cos l O O T i t
-2 B U j ^ = 4 c o s ( l 0 0 r t t - 7 i )
C u ^ = 4 cos 1007tt +
-2 D u ^ =4cosl007it
Huang dan gidi:
Phuong trinh song tai M la
Cau 19: M p t song c6 p h u o n g trinh u = 3eos(57tt + 0,047:x) ( e m ) , trong do >
dupe tinh bang cm, t dupe tinh bang giay Buoc song eiia song do la
A 70cm B 40em C 60cm D 50cm
Huang dan gidi:
2nx
T a c o 0,04Ttx = - X = 50cm Chpn D
Jau 20: Khoang each giiia hai ngon song lien tie'p tren mat ho la 3m Trong
jyipt phiit song dap vao bo 7 Ian Van {oc truyen song la
A 0,6 m/s B 0,2 m/s C 0,5 m/s D 0,3 m/s '
Huang dan gidi:
Chu k i eiia song la T = — = 10s; Van to'c truyen song v = — = 0,3m / s
6 T Chpn D
Cau 21: Song tai m p t diem M dao dpng voi chu ki T = 2s, van to'c truyen song la
V = 0,5 m/s Khoang each giiJa hai diem ngupe pha nhau gan nha't la
A 1,5m B I m C 2m D 0,5 m
Huang dan gidi:
Buoc song A, = vT = l m Khoang each giij-a hai diem dao dpng ngupe pha gan nhau nha't ^ = 0,5m
=> Chpn D Cau 22: M p t spi day dan hoi nam ngang co mpt dau co' dinh, mpt dau dao dpng voi bien dp a = 10cm va chu k i T = Is Chpn go'e thoi gian t = 0 k h i vat di qua vj tri co l i dp bang 0 theo chieu duong Phuong trinh dao dpng eiia song la
A u = 10eos(27it - 7i/2) (cm) B u = 10cos(27:t - n/2) (m)
C u = 10cos(27it + n/2) (em) D u = 10cos(27it + 7i) (m)
, Huang dan gidi:
Tanso a) = - ^ - 2 7 i ( r a d / s )
Khi t = 0 : U(3 = 0; Vj) > 0 Ta C O (p = - |
Phuong trinh dao dpng eiia song la u =10cos(27rt-Tc/2) ( e m ) C h p n A
£au 23: Tren mat mpt chat long tai O co mpt nguon song co dao dpng v o i tan
so f = 30Hz, van toe truyen song la mpt gia trj trong khoang l,6m/s < v <
2,9m/s Bie't tai diem M each O mpt khoang lOem, song tai d o luon dao dpng nguoc pha v o i dao dpng tai O Gia t r i van toe do la ,
A 2m/s B 4m/s C Im/s D l,2m/s
Huong dan gidi: (i
- Dao dpng tai M luon ngupe pha voi dao dpng tai O nen
27td 2df _ 6 fm^
2k + l ~ 2k + l l s
A(p = 7t + 2k7r = => V =
Trang 21Theo bai ra 1,6 m/s < v < 2,9 m/s => 1,6 < — ^ — < 2,9 => k = 1
2 k + 1
Vay van toe la v = 2m/s =i> Chon A
Cau 24; M p t nguon song co dao dong theo p h u o n g trinh u = A cos '37rt + ^ ' V 2 ; cm
trong do t do bang giay Khoang each giua hai diem gan nhat tren phuon^
truyen song ma pha dao dong lech pha nhau Zn/l la 0,75m Buoe song va van
toe truyen song Ian l u g t la
Cau 25: Tai diem S tren mat nuoc yen tinh co nguon dao dong dieu hoa theo
p h u o n g thang d u n g v o i tan so f K h i do tren mat nuoc hinh thanh he song tron
dong tam S Tai hai diem M , N nam each nhau 5em tren d u o n g thang d i qua S
luon dao dpng nguge pha voi nhau Biet toe dp truyen song tren mat nuoc la
80cm/s va tan so ciia nguon dao dpng thay doi trong khoang t u 48Hz den
64Hz Tan so dao dong ciia nguon la
A 64Hz B 48Hz C 54Hz D.56Hz
'» Huong dan gidi:
D p lech pha dao dpng ciia hai phan t u tren p h u o n g truyen song each nhau
Cau 26: Tai diem S tren mat nuoc yen tinh co nguon dao dpng dieu hoa theo
p h u o n g thang d u n g v o i tan so 50Hz K h i do tren mat nuoc h i n h thanh h$ song
tron dong tam S Tai hai diem M , N nSm each nhau 9em tren d u o n g th3ng di
qua S luon dao dpng ciing pha v o i nhau Biet rang, toe do truyen song thay doi
trong khoang t u 70cm/s den 80em/s Toe dp truyen song tren mat nuoc la
A.75cm/s B.80cm/s C 70em/s D.72em/s
Huang dan gidi:
pao dpng tai M luon ciing pha voi dao dpng tai N
' ^ ^ ^ ^ = cos(20t - 4x) (cm) (x tinh bang met, t tinh bang giay) Van toe truyen
song nay trong m o i t r u o n g tren bSng
Chpn B
£ l a ^ : M o t song truyen theo true Ox voi p h u o n g trinh u = acos(47:t - 0,02nx)
va X tinh bang cm, t tinh bSng giay) Toe d p truyen ciia song nay la
^Sa_30: M o t song co co chu k i 2 s truyen v o i toe dp 1 m/s Khoang each giua
diem gan nhau nhat tren mpt p h u o n g truyen ma tai do eac phan t u m o i
^'^^Ong dao dpng ngupe pha nhau la
A 0,5m B 1,0m C 2 , 0 m D 2,5 m
Trang 22Huang dan gidi:
Cau 31: Buoc song la khoang each giua hai diem
A tren cung mot phuong truyen song ma dao dong tai hai diem do ng^^^^
pha
B gan nhau nhat tren cung mot phuong truyen song ma dao dong tai hg,
diem do Cling pha
C gan nhau nhat ma dao dong tai hai diem do cung pha
D tren ciing mgt phuong truyen song ma dao dong tai hai diem do ciing pha,
Huang dan gidi:
Khoang each giira hai diem tren cung mot phuong truyen song ma dao
dong tai hai diem do nguoc pha la nua buoc song -> Dap an A sai
Buoc song la khoang each giua hai diem gan nhau nhat tren cung rrmt
p h u o n g truyen song ma dao dong tai hai diem do cung pha Dan an B dung;
C va D sai => Chon B
Cau 32: M o t nguon phat song co dao dong theo phuong trinh u=4oo6
4 Biet dao dong tai hai diem gan nhau nhat tren ciing mot p h u o n g truyen song
each nhau 0,5 m c6 do lech pha la n/3 Toe do truyen cua song do la :
Cau 33; Tai mot diem tren mat chat long co mpt nguon dao dong v o i tan so
120Hz, tao ra song on d j n h tren mat chat long Xet 5 ggn 161 lien tiep tren mP'
p h u o n g truyen song, 6 ve mot phi'a so voi nguon, ggn t h i i nhat each ggn thif
nam 0,5 m Toe do truyen song la
Cau 34: M o t song co Ian truyen trong mot moi truong H a i diem tren cung
p h u o n g truyen song, each nhau mot khoang bang buoc song co dao dgng
A Ciing pha B Nguge pha C lech pha n/2 D I?ch pha n/4
Huang dan gidi:
Hai diem tren cimg mot phuong truyen song, each nhau mot khoang bang
]piidc song thi dao dong ciing pha.-> Chon A
0jj_35: M o t song hinh sin truyen theo phuong Ox tii nguon O voi tan so 20Hz,
toe do truyen song nam trong khoang tir 0,7 m/s den 1 m/s Goi A va B la hai
^il'm nam tren Ox, 6 ciing mot phia so voi O va each nhau 10 em Hai phan tir
jfldi truong tai A va B luon dao dong nguge pha voi nhau Toe do truyen song la
A.lOOem/s B 80 em/s C 85 em/s D 90 cm/s
Huong dan gidi:
Cau 36: Hai diem M , N ciing nam tren mgt huong truyen song va each nhau
mot phan ba buoc song Bien do song khong doi trong qua trinh truyen Tai mot thoi diem, khi li do dao dong ciia phan tir tai M la 3 cm thi l i do dao dong cua phan tir tai N la -3 cm Bien do song bang
A 6 em B 3 em C 2 ^ cm D. 3N/2 cm
Huang dan gidi:
a cos cos (CO t) = 3
271"! _=>a =2N/3(cm) ^ C h g n C
a coscos c o t - - = - 3
£|u 37:Tren mat nuoc nam ngang, tai hai diem S^, S2 each nhau 8,2cm,
"guoi ta dat hai nguon song co ket hgp, dao dong dieu hoa theo p h u o n g fhang d u n g co tan so 15Hz va luon dao dong dong pha Biet van toe truyen song tren mat nude la 30cm/s, coi bien do song khong doi khi truyen d i So
<^'em dao dong voi bien do cue dai tren doan 8582 la
^^JL38: De khao sat giao thoa song ca, ngudi ta bo' t r i tren mSt nude nam
hai nguon ket hgp Si va 82 Hai nguon nay dao dgng dieu hoa theo
Trang 23p h u o n g thSng d u n g , cung pha Xem bien d p song k h o n g thay d o i trong
trinh truyen song Cac diem thupc mat nuoc va nam tren d u o n g t r u n g tryc ci;i^
doan S1S2 se ,
A dao dpng voi bien dp cue dai • fj.;, w v; , > "
i B dao dpng v o i bien dp cue tieu ,j ,Y>if, ,^ i t ; ,
t C khong dao dpng
D dao dpng vol bien dp bang nua bien dp cue dai
Huong dan gidi:
H a i nguon cung pha, cac cue dai giao thoa c6 d2 - d i = kA -> Cac diem thuoc
mat nuQc va nam tren d u o n g trung tryc ciia dogn S1S2 c6 d2 - d i = 0 se dao
dpng v o i bien dp cue dai -> Chpn A
Cau 39: Tai hai diem M va N trong m p t moi t r u o n g truyen song c6 hai nguCin
song ket h p p cung p h u o n g va cung pha dao dpng Biet bien dp, van toe cua
song khong doi trong qua trinh truyen, tan so' ciia song bang 40 H z va c6 sir
giao thoa song trong doan M N Trong dpan M N , hai diem dao dpng c6 bien do
cue dai gan nhau nhat each nhau 1,5 cm Van toe truyen song trong m o i truong
Cau 40: Tai hai diem A va B trong mpt moi t r u o n g truyen song c6 hai
nguon song ket hpp, dao dpng ciing phuong voi p h u o n g trinh Ian luot la
u ^ = acoscot va Ug = 2acos((ot + n) Biet van toe va bien dp song do m o i nguon
tao ra khong d o i trong qua trinh song truyen Trong khoang giua A va B c6
giao thoa song d o hai nguon tren gay ra Phan t u vat chat tai t r u n g diem cu'
doan AB dao dpng v o i bien dp bang
A O B.a/2 C.a D.2a
Huang dan gidi:
H a i nguon dao dpng ngupc pha, nen tai t r u n g d i e m cua doan AB '-'^
d2 - di = 0 se dao dpng voi bien dp cue tieu A = I ai - a21 = a Chpn C
Cau 41: O mat nuoc eo hai nguon song dao dpng theo p h u o n g v u o n g goc
mat nuoc, eo cung p h u o n g trinh u = Acoscot Trong mien gap nhau ciia IT"'
song, nhOng diem ma 6 do cac phan tir nuoc dao d p n g v o i bien dp eye dai
CO hi§u d u o n g d i cua song tix hai nguon den do bang
a
j A- "'^^ buoc song, 'p mpt so nguyen Ian buoc song
C mpt so' nguyen Ian nua buoc song
^ ^ D mpt so le Ian buoc song
Huang dan gidi:
^PlHai nguon dao dpng cimg pha nen n h u n g diem eo hi?u d u o n g d i ciia song
txx hai nguon den diem do bang mpt so' nguyen Ian buoc song se dao dpng v o i bien dp cue dai Chpn B
0aJ2: O be mat m p t chat long c6 hai nguon phat song ket h p p Si va S2 each nhau 20cm H a i nguon nay dao dpng theo p h u o n g thang d u n g eo p h u o n g
trinh Ian lupt la U j = 5eos407it (mm) va U2= 5eos(407it + n) (mm) Toe dp
truyen song tren mat chat long la 80 cm/s So diem dao dpng v o i bien dp cue dgi tren doan th^ng S1S2 la:
A 11 B.9 C.IO D.8 '
Huang dan gidi:
j^jjIlHai nguon dao dpng ngupc pha nen n h u n g diem dao dpng v o i bien dp eye dgi tren doan thang S1S2:
liai nam tren doan th^ng A B la
A 9 em B 12em C.6cm D 3 cm M
Huang dan gidi:
Khoang each ngan nhat giiia hai diem dao dpng v o i bien dp eye dai n a m
'fen doan th^ng A B la d = A/2 = 12/2 = 6 (cm) ^ Chpn C
^4^44: Dieu kien de hai song co k h i gap nhau, giao thoa dupe v o i nhau la hai phai xuat phat t u hai nguon dao dpng
A cung bien dp va eo hi^u so pha khong doi theo thoi gian
C eiing tan so, cung p h u o n g
CO ciing pha ban dau va ciing bien dp cimg tan so', cimg p h u o n g va co hieu so'pha khong doi theo thoi gian
Trang 24Huang dan gidi:
Dieu ki§n de hai song co khi gap nhau, giao thoa dugc v o i nhau la hai song
phai xuat phat t u hai nguon dao dong ciing tan so^ ciing phuong va c6 hi^u SQ
pha khong doi theo thai gian ^ Chon D
Cau 45: 6 mat chat long c6 hai nguon song A, B each nhau 20cm, dao dong
theo phuong t h i n g d u n g v o i phuong trinh la u ^ = Ug = 2cos507tt (t tinh bang
s) Toe do truyen song tren mat chat long la l,5m/s Tren doan thang AB, so
diem CO bien dp dao dong cue dai va so diem d u n g yen Ian lupt la
k = + 3 , ± 2 , ± l , 0
m = - 3 , ± 2 , ± l , 0 ^ Ch(?n C
Cau 46: Tai mat thoang ciia mpt chat long c6 hai nguon song Si va S2 dao dong
theo phuong thSng d u n g voi cung phuong trinh u = aeos407it (a khong doi, t
tinh hang s) Toe do truyen song tren mat chat long bang 80 cm/s Khoang each
ngan nha't giua hai phan t u chat long tren doan t h i n g S1S2 dao dpng voi bien
Cau 47: Tai mat chat long co hai nguon phat song ket hpp Si va S2 dao dpng
theo phuong vuong goe voi mat chat long co cung phuong trinh u = 2cos40n'
(trong do u tinh bang cm, t tinh bang s) Toe dp truyen song tren mat chat long
la 80em/s Gpi M la diem tren mat chat long each Si,S2 Ian lupt la 12cm va 9cm
Coi bien dp cua song truyen t u hai nguon tren den diem M la khong doi Pha"^
t u chat long tai M dao dpng vai bien dp la
0ii48: Hai nguon ket hpp Si va S2 each nhau 25 cm dao dpng voi tan so 25 Hz,
Cling pha tao hai song giao thoa voi nhau tren mat nuoe Van toe truyen song
1^ 1,5 m/s GiiJa S1S2 co bao nhieu gpn loi?
Caai9: Tai hai diem A va B tren mat nuoe dao dpng eimg tan so 16HZ, cung
pha, Cling bien dp Diem M tren mat nuoe dao dpng voi bien dp cue dai voi
MA = 30 cm, M B = 25,5 em, giifa M va duong trung true cua A B eon co hai day ci^c dai khae Van toe truyen song tren mat nuoe la :
P 9/ ^ = 6cm Hai diem CD nam tren mat nuoe ma ABCD la mpt hinh chix nhat
^ * 30em So diem cue dai va d u n g yen tren CD la
Trang 25Cau 51: Cho hai nguon ket hgp Si,S2 M,N nam tren d u a n g thang Si,S2
h l n h ve Tai N la van cue dai Tai M la van
Tai N la van cue dai thi tai M eung la van cue dai -> Chgn A
Cau 52: Tren mat nude eo hai nguon song Si va S2 dao d p n g cung pha ciing taV,
so'va cung p h u o n g con bien dg song khae nhau Bien do song tai nhirng dietn
ma hi^u khoang each den hai nguon bang mot sole Ian nua buoc song la
A bang 0 C cue tieu
B cue dai D khong xae d i n h dugc
Huong dan gidi:
Chgn dap an C, v i hai nguon song khong cung bien do nen tai n o i dao dong
cue tieu song tong hgp van con dao dgng, v o i bien do b i n g hi^u bien do cua
hai song thanh phan ma khong phai la bang 0, A = A , - A2 ^ 0 -> Chgn C
Cau 53: H a i nguon song nuoe A va B gio'ng nhau each nhau 12cm dang dao
dgng dieu hoa v u o n g goe v o i mat nuoe Buoc song la 1,6cm M la mot diem
tren mat nuoe each deu 2 nguon 1 khoang 10cm O la t r u n g diem A B So dium
dao dgng ngugc pha v o i nguon tren doan O M la
A 3 B.5 C 4 D 2
Huang dan gidi:
V i hai nguon gio'ng nhau nen nhOng diem tren O M dao dgng ngugc pha vm
nguon k h i chiing each hai nguon mot khoang bang mot sole Ian nua buoc song
d g n g v o i bien do
A 2a B a C 3a/2 D 0
Huang dan gidi:
Hai song UA va UB ngugc pha nhau nen tai trung diein song c6 bien dp bang 0
^ Chgn D
QiVi 55: Quan sat hien t u g n g giao thoa tren mat nuac duge t^o thanh do hai pguon ket h g p A va B cung pha dao dgng v o i tan so 15Hz, nhan tha'y ng c6 bien dg cue dai bac nhat ke t u d u o n g trung true ciia AB, la tai n h u n g diem eo j^i|u khoang each den A va B bang 3em Van toe truyen song tren mat nuoe la
Bien d g dao dgng tong hgp tai N c6 gia ^ A B N
tri b3ng bien d g tong hgp tai M va hang AOR- t i n s o r i X 6mm ^ Chgn D ^'^ §"02 ^o'"^
Cau 57: Song d u n g xay ra tren day dan hoi c6 hai dau co d i n h k h i ' "
A Chieu dai day bang mot phan t u bu6c song '
-B Buoc song gap doi chieu dai day ' 'nl
C Chieu dai day bang bgi so nguyen Ian nua buoc s o n ^ ' ' "
' / • r> rg? n*^' j
D Chieu dai day bang mgt so le buoc song
, ,x 'A h i\mdl ,A
Huang dan giat:
Song d i m g xay ra tren day dan hoi eo hai dau eo d i n h k h i chieu dai day bang mgt so nguyen Ian nua buoc song -> Chgn C ,13 G ^ 1 ^ • - i j
£au 58: Song d u n g , hieu so pha cua phan t u doi x u n g qua niit la gr, 0:.- — |
A 0 B 71 C.27t D.jr/2
Huang dSngiAi:'-' f - " V - «' ^OM : £ d n i 2
Cac phan t u d o i x u n g qua niit thi ngugc pha nhau nen hi^u so pha A y ^^a
mh u^i^ A
C h g n B „ ^ _
Trang 26Cau 59; K h i c6 song d u n g tren soi day dan hoi thi
A N g u o n phat song d u n g dao dpng
B Tren day c6 n h u n g diem dao dpng eye dai va eye tieu '
C Tren day chi eo song tai ' ' '
D Tat ca eae diem tren day khong dao dong
Huang dan gidi:
K h i CO song d u n g tren spi day thi tren day c6 nhCrng diem dao dpng v6i
bien dp eye dai va eye tieu -> Chpn B
Cau 60: K h i c6 song d u n g tren mpt spi day dan hoi thi khoang each giiia hai
nut song lien tiep bang
A.m B.X C.2> D.X/2
8 " " ^ ' Huang dan gidi:
S"Kktiang each gii>a hai nut lien tiep bang mpt nua buoc song -> Chpn D
'^au'^y: K h i c6 song d u n g tren mpt spi day ma hai dau dupe giu co djnh thi
buoc song b^ng
A H a i Ian khoang each giOa hai niit gan nhau nhat
B H a i Ian dp dai day
C Kboang each giOa hai bung gan nhau nhat
D D p dai cua day
^ ~s Huong dan gidi:
Khoang each giCJa hai niit lien tiep bSng khoang each giua hai bung lien tiep
nen buoc song se bang hai Ian khoang each giOa hai niit gan nhau nhat hoac
hai Ian khoang;fap]r|{giii'a hai bung gan nhau nha't.^ Chpn A
Cau 62: Trong thi nghiem ve song dung, tren mot spi day dan hoi dai 1,2m voi
hai dau eo' djnh, nguoi ta quan sat tha'y ngoai hai dau day co' djnh eon co hai
diem khac tren day^|^^ng dao dpng Bie't khoang thoi gian giCra hai Ian lien
tiep spi day duoi thang la 0,05s Van toe truyen song tren day la
Cau 63: M p t la thep mong, mpt d|u^eo djnh, dau con lai dupe kich thich de dao
done voi chu^ki khong d o i va bar\ 0,08s A m do la thep phat ra la
A sieu am B ha am
C nhae am D am ma tai nguoi nghe dupe
Hu&ng dan gidi:
1
Tan so ciia am phat ra la f = — = 12,5Hz
:=> A m do la thep phat ra la h ^ am Chpn B
Q^u6i: H a i buoc song cong h u o n g Ion nhat ciia mpt 6'ng chieu dai L, hai dau
(lO la bao nhieu? >-,
Cau 66: M p t spi day manh dan hoi dai lOOem eo hai dau A, B eo'djnh Tren day
CO mpt song d u n g vol tan so' 60Hz va eo 3 niit song khong ke A va B Buoc
song va toe dp truyen song tren day la:
£|u_67: Thue hien song d u n g tren day AB co chieu dai 1 voi dau B co djnh, dau
A dao dpng theo phuang trinh u = acos27:ft Gpi M la diem each B mpt doan d,
buoc song la X, k la cac so nguyen Khang djnh nao sau day la sai?
kX
A Vj tri cac niit song dupe xac djnh boi cong thuc d = —
B Vj t r i cac byng ^ong dupe xac djnh boi cong thiic d = (2k +1)—
Trang 27C Khoang each giCra hai b y n g song lien tiep la d = —
D Khoang each g i i i a m o t n u t song va mot b u n g song lien tiep la d = —
4
Huang dan gidi: , ,:
K h i CO song d u n g ta co Khoang each giiia hai b u n g song lien tiep la d = ^
2 ' Khoang each giua m o t n u t song va m o t b u n g song lien tiep la d = ^ ; Vj t r i cac
niit song dugc xac d i n h b o i cong thuc d = — Dap an B la sai -> Chpn B
Cau 68: Mgt day dan hoi A B dai 60 cm co dau B co djnh, dau A mac vao mpt
nhanh am thoa dang dao d o n g v o i tan so f = 50 Hz K h i am thoa rung, tren d a y
CO song dirng v o i 3 b u n g song Van toe truyen song tren day la
A v=15m/s B v = 28m/s C v = 20m/s D v = 25m/s
Huang dan gidi:
3X "\
Chon C 1=- > = 4 0 ( c m )
v = 2000 cm = 20
2 •
v = Xf
Cau 69: M o t soi day dan hoi dai 100 em, co hai dau A, B co djnh M o t song
truyen v o i tan so 50 Hz, tren day dem dugc 5 n i i t song, ke ca hai n i i t A, B Van
toe truyen song tren day la:
Cau 70: M o t sgi day dan hoi dai 130 cm, co dau A co djnh, dau B t u do d a o
d g n g v o i tan so 100 Hz, van toe truyen song tren day la 40 m/s Tren day co
bao nhieu n i i t va b u n g song:
A CO 6 n u t song va 6 b u n g song B eo 7 niit song va 6 b y n g song
C CO 7 n i i t song va 7 b u n g song D co 6 niit song va 7 b u n g song
Huang dan gidi:
v = Xf
130 = ( 2 k + 1)10
X = j = 0 , 4 ( m ) =i>k = 6
So b u n g va so niit tren day la k + 1 = 7 Chpn C
0 u _ 7 1 : M o t sgi day A B dai 21 cm, van toe truyen song tren day la 4 m/s, dau
j!^ dao d o n g v o i tan so 100 H z Tren day co song d u n g hay khong? So b u n g
gong k h i do la:
A Co, CO 10 b u n g song B Co, eo 11 bung
C Co, CO 12 b u n g song D Co, eo 25 b u n g song '
Huang dan gidi: - "
T u o n g t u cau 70, = J = 0,04(m) = 4 ( c m ) Khi do chieu dai day 1 = 21 =(2.10 + 1) A/4 V i vay tren day co song d u n g va
so b u n g song l a k + l = l l ^ Chon B
Cau 72: Trong he song d u n g tren mot sgi day ma hai d a u dupe giir co d i n h ,
buoc song bang:
A D o dai cua day
B M o t nua do dai cua day ;
C Khoang each giiia hai niit song hay hai b u n g song lien tiep
D H a i Ian khoang each giira hai niit song hay hai b u n g song lien tiep
Huong dan gidi:
Voi song d u n g , khoang each giira hai niit lien tiep hay hai b u n g lien tiep la nua buoc song N e n buoc song bang hai Ian khoang each g i u a hai n i i t song hay hai b u n g song lien tiep Chpn D
Cau 73: M o t sgi day eo chieu dai 1 = 68em, tren day eo song d u n g Biet rang
loang each giCra 3 n i i t song lien tiep la 16 em, m p t dau day eo djnh, dau con lai dugc t u do So'bung song va niit song co tren day Ian l u g t la:
A 9 v a l 0 B 9 v a 8 C 8 va 9 D 9 v a 9
Huang dan gidi:
- Khoang each giCia 3 niit lien tiep la 16cm, nen A = 16 c m
{2k + l)X
- M o t dau day eo d i n h , dau con lai t u do nen chieu dai day 1 =
k = 8 Vay tren day co 9 n i i t va 9 bung Chon D
£au 74: Tren m o t sgi day dai 2 m dang eo song dirng v o i tan so lOOHz, n g u o i ta thay ngoai hai d a u day co d j n h con co 3 d i e m khae dang d i i n g yen V a n toe truyen song tren day la
Trang 28Cau 75: Mpt day dan hoi 2 dau co'djnh dai 40cm, khi day dao dpng voi tan so
f = 600Hz, ta quan sat tren day co song dung voi hai bung Buoc song la
A 13cm B 20cm C 40cm D 80cm
Huang dan gidi: fij - r
Tren day co hai bung nen \ X=>X = 40cm Chon C ; v,
Cau 76: Cho mpt sgi day dan hoi dai 40cm Hai dau co djnh, cho day dao dono
voi tan so f = 600Hz Ta quan sat thay co song dirng tren day voi hai byng
song Van toe song tren day la
A 79,8m/s B 120m/s C 240m/s D 480m/s
Huong dan gidi:
Tren day co hai bung song nen X = \ 40cm; •
Van toe song la v = X,f = 240m/s ^ Chgn C
Cau 77: Mgt song dung tren day dugc mo ta bai phuong trinh:
A 80cm/s B 60cm/s C 20cm/s D 40cm/s
Huang dan gidi:
Ta CO
v = Xi [v = 80(cm/s) Chpn A
Cau 78; Mpt sgi day cang ngang 2 dau co dinh dai 1 = 2m Nguoi ta tgo ra song
dung tren day voi tan so nho nha't f de lai co song dung phai tang tan so them
it nha't la 50 Hz Van toe truyen song tren day la
Cau 79; Mpt sp-i day dai 1 = 1,5m, hai dau codinh nguoi ta kich thich de tren
day CO song dung Buoc song ngan nha't thoa man la bao nhieu ?
A 6m B 1,5m
C 3m D Khong xac djnh dupe
214
Huang dan gidi:
CI bai nay hoc sinh thuong nham Ian giira buoc song "ngan" nha't va "Ion"
phat an X, = 21 = 3m Thyc te thi buoc song ngan nha't ta khong
^ac djnh dugc => Chon D
^au 80: Mpt song dung dugc t^o ra boi giao thoa cua hai song chay, tan so'
300Hz, CO khoang each ngSn nha't giiia mpt nut va mpt bung song la 0,75m
V?n toe cua cac song chay do hang
A lOOm/s B 200m/s C 450m/s D 900m/s
Huang dan gidi:
Khoang each giua mpt niit va mpt byng song bang:
d = - = — = > v = 4df = 900(m/s)
QiuSl- Tren mpt spi day co chieu dai 1, hai dau co' dinh, dang co song dirng
Tren day co mpt bung song Bie't v^n toe truyen song tren day la v khong doi
Tan so cua song la
Trang 29nvm V4t Li 12, t^p 1 - Nguyen ^luang L g c
Cau -4: M p t spi day chieu dai 1 c5ng ngang, hai dau co'dinh Tren day dang co
sor-' d i m g v o i n b y n g song, toe dp truyen song tren day la v Khoang thoi gigp,
g l i i a hai Ian lien tiep spi day d u o i thang la
vai m p t nhanh ciia am thoa dao dpng dieu hoa v o i tan so 20Hz Tren day AB
CO m p t song d u n g on dinh v o i 4 bung song, B dupe coi la nut song Toe do
truyen song tren day la
Cau 86: M p t spi day A B dai 100 cm cang ngang, dau B co' dinh, dau A gan voi
mpt nhanh ciia am thoa dao dpng dieu hoa v o i tan so 40 H z Tren day AB co
i r p t song d u n g on dinh, A dupe coi la nut song Toe dp truyen song tren day In
r^n 87: Tren mpt spi day dan hoi dang co song d i m g Khoang each t u m p t nut
d"'n not bung ke no bang
A M p t nua bude song B hai buoe song
C M p t phan t u buoe song D mpt buoe song
Huong dan gidi:
Khoang each tit m p t niit den m p t b y n g ke no bSng m p t phan t u buoe song
Cau 89: Tren m p t spi day eo song d u n g v o i buoe song la X Khoang each giira
hai niit song lien ke la
CO song d u n g , tan so song la 50 H z K h o n g ke hai dau A va B, tren day co 3 niit
s6r\g Toe dp truyen song tren day la
d t t ^ : D p cao la m p t dac t r u n g sinh l i ciia am p h u thupe vao:
A van toe am B tan so am
C bien dp am D nang l u p n g am
Huang dan gidi:
E)p cao la dac trung sinh l i ciia am, phu thupe vao tan so'am => Chpn B
^*3]t92: H a i am thanh co am sac khae nhau la do: ^ „
A khae nhau ve tan so'
B dp cao va dp to khae nhau
C tan so, bien dp ciia cae hoa am khae nhau
so l u p n g va cuong dp ciia cac hoa am khae nhau
•ot.fi
Trang 30Huang dan gidi: |
A m sac la mpt dac trung sinh l i cua am, phu thupc vao tan so' am, bien (J^
song am va cac thanh phan cau tao ciia am => Chon C
Cau 93: Song am khong truyen dupe trong moi truong nao?
A Ran B Long C Khi D Chan khong
Huang dan gidi:
Song am khong truyen dupe trong chan khong => Chpn D
Cau 94: Chpn cau sai: Song am la
A Song dpc truyen trong cac moi truong vat cha't
B Song CO tan so t u 16Hz den 20000Hz, con nguoi c6 the cam nhan dupe
C Khong truyen dupe trong moi truong chan khong
D Song ma van toe khong doi
Huang dan gidi:
Van toe cua song am c6 the thay doi dupe => Chpn D
Cau 95: Dp to cua am khong phu thupc vao ye'u to'nao?
A Tan so B Bien dp
C Buoc song D.Mue cuong dp am
Huang dan gidi:
Dp to ciia am phu thupc vao cuong dp am (tuc phu thupc vao bien dp); phu
thupc vao tan so am va muc cuong dp am Dp to ciia am khong phy thupc vao
buoc song Chpn C
Cau 96: Dp cao ciia am dupe dac trung boi ye'u to nao:
' A Tan so B Buoc song
C Muc cuong dp am D Bien dp
Huang dan gidi:
Dp cao ciia am la mpt dac tinh sinh li ciia am, phu thupc vao tan so'
=> Chpn A
Cau 97: Dp to eiia am dupe dac trung boi:
A Muc ap sua't am thanh B Miic cuong dp am
C Bien dp dao dpng D Cuong dp am
Huatig dan gidi:
Dp to ciia am dupe dac trung boi muc cuong dp am -> Chpn B
Cau 98: Khi am truyen t u nuoc vao khong khi thi tan so, buoc song thay d*^'
nhu the nao?
A Ca hai deu giam
B Ca hai deu tang
C Tan so'khong doi, buac song giam
D Tan so tang, buoc song giam
Huang dan gidi:
jChi arn truyen t u nuoc sang khong khi thi tan so' khong doi, con van to'e giam do do buoc song giam => Chpn C
CaU trong moi truong nao nho nhat:
A Ran B Khi C.Long D Chan khong
Huang dan gidi:
Trong chan khong am khong truyen dupe, v i the van toe am trong chan khong la "ho nhat -> Chpn D
g|uJOO: Don vj ciia cuong dp am la:
A.N/m^ B W / m l C W/S D NAV
Huang dan gidi:
Don vj ciia cuong dp am la W/m^ => Chpn B
fau 101: Don vj ciia muc cuong dp am la :
A.Ben B Becoren C Tesla D H e n r i
Huang dan Becoren la don vj ciia dp phong xa Tesla la don vj ciia cam ung t u Henri la
don vj ciia dp t y cam => Chpn A
Cau 102: Phat bieu sai la :
A Nhae am la do nhieu nhae cy phat ra
B Tap am la cac am c6 tan so' khong xae dinh
C Dp cao ciia am la mpt dac tinh sinh li ciia am
§ A m sac la mpt d^e tinh sinh li ciia am
Huang dan gidi:
Nhae am la cac am eo tan so xae djnh Chpn A
£|JL1Q3: Chpn phat bieu dung :
t A m to hay nho phy thupc vao muc cuong dp am va tan so'am
A m CO tan so cang Ion thi tai ta eo cam giae cang to
A m CO cuong dp nho thi tai ta cam giae am nho
A m CO cuong dp Ion thi tai ta c6 cam giae am do to
Huang dan gidi:
to hay nho phy thupc vao muc cuong dp am va tan so'am
=*ChonA
"^41104: Dao dpng am tong hop la dao dpng Jjl^ Tuan hoan B Hon loan C Dieu hoa D T y do
Trang 31„ , tap- •^„^, ^, „
Huchtg dart gidi:
Dao dpng tong hap la dao dpng tuan hoan -> Chpn A ' "
Cau 105: Song sieu am la n h u n g song am
A M a tai nguoi khong nghe tha'y dupe '
B D o may bay sieu am phat ra
C Co tan so gan n g u o n g tren 20kHz ma tai nguoi cam nhan dupe
D Co tan so'Ion han 20kHz
Huang dan gidi:
Song sieu am la nhi>ng song am c6 tan so Ion hon 20000Hz => Chpn D
Cau 106: Hai am thanh c6 am sac khac nhau la do
A Tan so'khac nhau
B D p cao va dp to khac nhau '
C So'lupng cac hpa am khac nhau
D So l u p n g va cuong dp cac hpa am khac nhau
Huong dan gidi: ^'
A m sac p h u thupc vao so'lupng va cuong dp cac hpa am =>Chpn D
Cau 107: A m d o hai nhac cu phat ra luon khac nhau ve
" A A m sac B D p to C Dp cao D.Tan so
Huong dan gidi:
A m do hai nhac cu phat ra luon khac nhau ve am sac => Chpn A
Cau 108: Phat bieu nao sau day la sai khi noi ve song am :
A A r n sac la m p t dac tinh vat li ciia am phu thupc tan so va bien dp
B NhOng am nghe dupe c6 muc cuong dp am tir 0 dB den 130dB
C D p to la dac tinh sinh l i ciia am phu thupc tan so'va m i i c cuong dp am
D A m do nhac cu va con nguoi phat ra la tong hpp ciia cac am co ban
hpa am ^'
Huang dan gidi:
A m sac la dac tinh sinh ly cua am nen dap an A la sai => Chpn A
Cau 109: H o p dan c6 tac d u n g :
A V u a khuye'eh dai am ,vua tao am sac rieng cua am do dan phat ra
B Tranh dupe tap am va tieng on lam cho tie'ng dan trong treo
C G i i i cho am phat ra c6 tan so xac djnh
D L a m tang dp to va dp cao cua am
Huang dan gidi:
H o p dan c6 tac d u n g khuye'eh dai am va tao am s^c rieng cua am do
phat ra => Chpn A
'aU 110: C u o n g dp am dupe xac djnh bang :
A p sua't tai m o i t r u o n g ma song am truyen qua
B Binh p h u o n g bien dp dao dpng ciia cac phan t u m o i t r u o n g (tai d i e m ma song am truyen qua)
C. N a n g l u p n g ma song am truyen trong mpt d o n v j thoi gian qua m p t d o n
v i di?n tich (dat v u o n g goc v a i p h u o n g truyen song)
p Co nang toan phan cua cac phan t u trong mpt don v i the tich ciia moi
t r u o n g tai d i e m ma song am truyen qua
Huang dan gidi:
Cuong dp am dupe xac dinh bang nang l u p n g ma song am truyen trong mpt don vi thoi gian qua mot don vj dign tich (dat v u o n g goc v o i p h u o n g
truyen song) => Chpn C :,ir' ,
A C u o n g dp am B Nhi?t dp cua moi t r u o n g »'
C Mat dp cua moi truong D T i n h dan hoi ciia m o i truong
Huang dan gidi:
Van toe am thanh phii thupc vao ban chat cua moi truong, nhi^t dp ciia moi truong va khong phu thupc vao cuong dp am =i> Chpn A
Cau 112: Khi song am truyen tir moi truong khong khi vao moi truong nuoe thi
A chu kl cua no tang B tan so'ciia no khong thay doi
B buoe song ciia no giam D buoc song ciia no khong thay doi
Huang dan gidi:
Khi song am truyen tu moi truong khong khi vao m o i t r u o n g nude thi tan
so ciia no khong thay doi => Chpn B
Cju 113: Van toe am truyen trong nuoe la 1344m/s, trong khong k h i la 336m/s
Khi am truyen tu khong khi vao nude, buoe song thay doi n h u the nao?
A Tang 4 Ian B Giam 4 Ian C Tang 2 Ian D Giam 2 Ian
Huang dan gidi:
Khi am truyen t u khong khi vao nuoe thi tan so khong thay doi nen
Trang 32Huang dan gidi:
Buoc song A = v/f = 3m Khoang each giua hai diem gan nhau nhat, vuong
pha nhau la A/4 = 0,75 m => Chpn A
Cau 115: M o t hgc sinh go vao mpt thanh thep dai de tao am H a i diem g^Y,
nhau nhat dao dpng ngupc pha each nhau 2m Van toe truyen am trong thep
1200m/s Tan so am phat ra la
A.500HZ B 600Hz C 400Hz D 300Hz
Huang dan gidi:
Hai diem dao dpng ngupc pha gan nhau nhat la A/2 = 2 m ^ A = 4m
Vay f = - = 300Hz => Chpn D
Cau 116: Van toe am trong nuoc la 1360m/s, trong khong k h i la 340m/s Khi
truyen am tir nuoc ra khong khi, tan so am thay doi the'nao ?
A Tang 4 Ian B Giam 4 Ian C Khong doi D Giam 2 Ian
Huang dan gidi:
Khi am truyen t u m o i t r u o n g nay sang m o i truong khae thi tan so khong
thay doi ->Chpn C
Cau 117: Hpc sinh A gpi hoc sinh B Sau khi gpi nhau dupe 0,25 giay thi hoc
sinh B nghe thay tieng hpc sinh A gpi Biet AB = 85m Van toe truyen am trong
khong khi la
A.330m/s B 340m/s C 335m/s D 345m/s
Hu&ng dan gidi:
Van toe truyen am trong khong khi v = AB/t = 340 m/s => Chpn B
Cau 118: M u c cuong dp am cua hai am la L = 20dB Cho biet cuong do am
chuan la Io= lO-i^ W / m l Cuong dp am nay la
=> Chpn C
AS IS?!}
0 j j J 2 O : Tai mot diem A nam each nguon am N (nguon diem) m o t khoang
^fi, = lm, CO muc cuong dp am la L A = 90dB Biet nguong nghe ciia am do
^|uJ21: K h i am truyen tix khong khi vao nuoc, buoc song cua no thay doi the
pao? Cho biet van toe am trong nuoc la 1550 m/s, trong khong k h i la 340 m/s
A Khong thay doi B Giam d i 4,56 Ian
C Tang len 4,56 Ian D Tang len 1210 m
Huang dan gidi:
Ta c6X' = X.~ = 4,56X => Chpn C
n Caul22: H a i am hon kem nhau I d B ve dp to Tl so cuong dp am cua hai am
£a!Ll23: Tai diem A each xa nguon am N mpt khoang N A = 2m M u c cuong
"^^9 am la LA = SOdB Cuong dp am chuan la lo = lO'^ W/m^ M u e cuong dp am
Trang 33Cau 124: M p t nguon phat am dang huong c6 cong sua't P = 1,256W Coi ttiQj
truang khong hap thu am Cuong dp am chuan la lo = 10 '^W/m^ M i i c cuoj^
dp am tai diem each nguon 100m la
Cau 125: O ngoai trai mpt am c6 do to 70 dB Trong phong, am nay chi c6 do to
40 dB Tinh ti so'cuong dp am 6 hai nai Bie't moi truang khong hap thu am
A 1000 B 1100 C.1050 D 980
Huang dan gidi:
Theo gia thie't
L2 - L i = 1 0 1 o g ^ - 1 0 1 o g i - = 101og-^ = 3 0 = ^ ^ = 10^ =100 ^ Chpn A
^0 ^0 ^1 ^1 Cau 126: Cho mpt ong try chua nuac, dung mot am thoa tao ra dao dpng Am
a mieng ong manh nhat 6 Ian 1 va Ian 2 ung vai khoang each tir mi?ng ong deh
mat nuoc la 75mm va 25mm Bie't rang van toe truyen am trong khong khi
X 0,1
Cau 127: M p t nhac cu phat am voi tan so ca ban f = 630Hz M p t nguai c6 the
nghe am den tan so cao nhat la 18000Hz Tan so am cao nhat ma ngudi na)'
nghe dupe do nhac eu tren phat ra la
A 18000Hz B 17000Hz C 17800Hz D 17640Hz
i Huang dan gidi:
Tan so'eae hpa am ma nhac cu phat ra la fh = kf = 630k k e N *
630k < 1 8 0 0 0 - > k < 28,57
' Tan so'am cao nhat ma tai nguai nay nghe dupe do d u n g cy tren phat ra l*"
fm x = 28.630 = 17640Hz Chpn D
Cty TNHH MTV DWH Khang Vi(t
0^i_128: M p t spi day dan hoi cang ngang, dang c6 song d u n g on djnh Tren
day/ A 1^ "^^^ diem niit, B la diem bung gan A nhat v o i AB = 18 cm, M la mpt jie'rn tren day each B mpt khoang 12 cm Bie't rang trong mpt chu ky song, Ichoang thoi gian ma dp Ion van to'c dao dpng ciia phan t u B nho hon van toe eye dai eua phan t u M la 0,1s To'c dp truyen song tren day la:
A 3,2m/s B.5,6m/s C 4,8 m/s D.2,4m/s
Huang dan gidi:
Khoang each A B ^ "-^ = 18cm, =>X = 72cm, M B = 12cm => khoang thai gian
song d i dupe 24em, hay —X la —T = 0,1s => T = 0,3s va van toe truyen song
A 10 Hz B 12Hz C.40HZ D 50 Hz
Huang dan gidi:
Ban dau chieu dai day 1 = 2X, sau do 1 = X', suy ra tan so f = f/2 = lOHz jvi >
Chpn A
Cau 130: Trong qua trinh truyen song, khi gap vat can t h i song bj phan xa Tai
diem phan xa t h i song tai va song phan xa se I , u A
A luon cung pha B khong eung loai
C luon ngupe pha D cimg tan so
Huang dan gidi:
Trong qua trinh truyen song, khi gap vat can thi song bj phan xa Neu diem phan xa la co d j n h thi song tai va song phan xa ngupe pha nhau, neu diem phan xa la t u do thi song toi va song phan xa se cung pha nhau Tai diem phan thi song tai va song phan xa se cung tan so' => Chpn D
^'^ moi truong 6 hai diem n^m tren cung mpt hudng truyen song va each nhau '^9t so' nguyen Ian buoc song thi dao dpng
f cung pha nhau r,,, B l^ch pha nhau ^ n
-l?ch pha nhau — D ngupe pha nhau i^n'.-" ^
Trang 34Huang dan gidi:
Cac phan t u m o i t r u o n g 6 hai diem nam tren cung m o t h u o n g truyen son^
va each nhau m p t so nguyen Ian buoc song thi dao d o n g ciing pha nhau
=> Chon A
Cau 132: Tren m p t spi day dan hoi dang c6 song d u n g Bie't khoang each ng^^^i
nha't giCra m p t n u t song va vj t r i can bang cua mpt b u n g song la 0,25m Song
truyen tren day v d i buoc song la
A 0,5 m B 1,5 m C 1,0 m D 2,0 m
Huong dan gidi:
Khoang each ngan nha't giCra mot nut song va vj t r i can bang ciia mpt b u n ^
songla j , n e n j = 0 , 2 5= > > L = l ( m ) = > C h p n C
Cau 133: M p t song a m truyen trong k h o n g k h i v d i toe dp 340 m/s va budc song
34 cm Tan so cua song am nay la
Cau 134: M p t song h i n h sin truyen theo chieu d u o n g ciia true Ox v d i phuong
trinh dao d p n g ciia nguon song (dat tai O) la u„= 4cosl007tt (cm) 6 diem M
(theo h u d n g Ox) each O mpt phan t u budc song, phan t u m o i t r u o n g dao dong
vdi p h u o n g trinh la
A u^^ = 4cos(1007tt + n) (cm) B u^^ = 4cos(1007tt) (cm)
C u ^ = 4cos(1007rt - 0,57r) (cm) D u^^ = 4cos(1007it + 0,57i) (cm)
Huang dan gidi:
Cau 135: T r o n g m p t t h i n g h i e m ve giao thoa song nude, hai n g u o n song k^''
hpp dupe dat tai A v a B dao dpng theo p h u o n g trinh u ^ = U g =aeos25Kt
(a k h o n g ddi, t tinh b a n g s) Tren doan thSng AB, hai d i e m cd p h a n t u nii'^^
dao d p n g v d i bien d p c u e dai each nhau mpt khoan g ngSn nha't la 2 em Toe i'^'
truyen s d n g la
A 25cm/s B lOOcm/s C 75 cm/s D 50 cm/s
Huang dan gidi:
Tren doan thang AB, hai d i e m cd phan t u nude dao d p n g v d i bien dp cue (J^i each nhau m p t khoang ngan nha't la ^ nen A = 4 em / >
Toe dp t r u y e n sdng la v = A.f = 4.12,5 = 50 em/s =:> Chpn D - •'
^^u_136: T r o n g m p t t h i nghiem ve giao thoa sdng nude, hai n g u o n sdng ket
^op dao dpng ciing pha dupe dat tai A va B each nhau 18 em Sdng t r u y e n tren
mat nude v d i budc sdng 3,5 em Tren doan AB, so d i e m ma tai d d p h a n t u nude dao d p n g v d i bien dp cue dai la
A 9 B 10 C 12 D 11 : n ; s ! ' ;
Huong dan gidi: '
-Ta ed hai n g u o n dao d p n g eiing pha nen:
A.11/120S B l/60s C.1/120S D.l/12s
Huang dan gidi:
X = j= 12cm Khoang each M N = 26em = 2X+^X
Khoang thdi gian ngan nha't At = ^ T = ^ s => Chpn B
£au 138*: H a i nguon phat sdng ket hop A, B v d i A B = 16em tren mat thoang chat long, dao d p n g theo p h u o n g t r i n h :
=5cos(307if)mm; U g =5eos 30nt +
-2 m m Coi bien dp sdng k h o n g doi, toe dp sdng v = 60cm/s G p i O la t r u n g d i e m eiia
AB, d i e m d u n g yen tren doan A B gan O nha't va xa O nha't each O m p t doan
t u o n g u n g l a : y / :
A 1 em; 8 cm B 0,25 em; 7,75 em
C 1 em; 6,5 em > D 0,5 cm; 7,5 em :
Trang 35Huang dan gidi:
Ta CO X-•= — = — = 4cm
f 15
Bien dp cua dao dpng tong hpp A = 2acos Ad n
Diem khong dao dong c6
Ad^i„ =0,25A = l c m = > d 2 = 8 , 5 = > x ^ i „ = 8,5 - 8 = 0,5cm => Chpn D
Cau 139*: Hai nguon song ket hgp A, B tren mat thoang cha't long dao dong
theo phuong trinh = Ug = 4cos(l07tt)mm Coi bien dp song khong do'i, toe
dp song V = 15cm/s Hai diem M j , cung nSm tren mpt elip nhan A, B lam
tieu diem c6 A M j - B M j = l c m va A M j - B M 2 = 3,5cm Tai thai diem li do
cua M l la 3mm thi li dp ciia M2 tai thai diem do la
A 3mm B -3mm C - \ ' 3 m m D -3N/3 mm
Huang dan gidi:
Hai nguon gio'ng nhau, c6 = 3cm nen
U w =2.4cos7t- Adi -cos ( O t - T t d j + d j
IJau 140*: Mpt nguon phat song dao dpng dieu hoa tao ra song tron dong tam
C 'ruyen tren mat nude voi budc song X Hai diem M va N thupc mat nuoc,
:1m tren hai phuong truyen song ma cac phan tu nude dang dao dpng Bit't
O M = 8X, O N = 12X va O M vuong gdc vdi O N Tren doan M N , so' diem ma
phan tu nude dao dpng nguac pha vdi dao dpng cua nguon O la
- A 5 B.4 C 6 D 7
Ta CO hinh ve ben: M + O H = O M O N / M N = 6,656 X
+ So diem dao dpng nguoc pha vdi figuon tren doan M H la:
O H < (k + 0,5)X < O M <
6,656 < (k + 0,5) < 8 ^ 6,156 < k < 7,5
^ k = 7 O + So' diem dao dpng ngupc pha vdi nguon tren doan H N la :
O N < (m + 0,5)?i < O N hay 6,656 < (m + 0,5) < 12 -> 6,156 < m < 11,5 -> m = 7, 8, 9,10, 11 -> CO 5 diem
Vay so' diem ma phan tu nude dao dpng nguac pha vdi dao dpng cua nguon O tren doan M N la 6 diem => Chpn C
Cau 141: Tren mpt spi day dan hoi dai I m , hai dau codinh, dang cd sdng dung vdi 5 niit sdng (ke ca hai dau day) Budc sdng cua sdng truyen tren day la
A I m B 1,5m C 0,5m D 2m
Huang dan gidi: ^^^^^
Tren day cd 5 nut sdng => 1 = 4A/2 •^X = 2.1/4 = 0,5m Chpn C '
Cau 142: Tren mpt dudng thSng co dinh trong moi trudng dang hudng, khd-^e hap thu va phan xa am, mpt may thu d each nguon am mpt khoang d thu dirv
am cd muc cudng dp am la L ; khi djch ehuyen may thu ra xa nguon am the.i '
m thi muc cudng dp am thu duac la L - 20 (dB) Khoang each d la
£au 143*: Trong mpt thi nghiem ve giao thoa sdng nude, hai nguon sdng L^
hpp O i va O2 dao dpng cimg pha, cung bien dp Chpn h^ tpa dp vuong -^L
Oxy (thupc mat nude) vdi go'c tpa dp la vi tri dat nguon O i con nguon O2 n"'
tren trye Oy Hai diem P va Q n i m tren Ox cd O P = 4,5 em va O Q = 8cm D,^' chuyen nguon O2 tren trye Oy den vj tri sao cho gdc PO2Q cd gia tri Idn r ' - c thi phan tu nude tai P khong dao dpng eon phan tu nude tai Q dao dpng voi hien dp cue dai Biet giiia P va Q khong con eye dai nao khac Tren doan OF
^iem gan P nha't ma cac phan tu nude dao dpng vdi bien dp eye dai each P nipt doan la
A 1,1cm B 3,4 cm C 2,5 cm D 2,0 cm
229
Trang 36Huong dan gidi:
Dat cac goc 0,03^ = 0,02Q = (?2
Dau "=" xay ra khi a = 6cm Theo gia thie't khi do phan t u nuoc tai P khon^
dao dong con phan t u nuoc tai Q dao dpng voi bien cue dai va giOa P va Q
khong con eye dai nao khac nen
Gpi M la diem gan P nha't dao
dong voi bien do cue dai, khi do tai
J Mach dao dpng, dao dpng d i f n t u
3 Mach dao dong
Mach dao dong la mot mach dien khep kin gom mot ty dien c6 d i f n dyng C ni3c noi tiep vai mot cuon day thuan cam, c6 do t u cam L. fi-pmr'
IJ Dao dong di^ tit tu do trong mach dao dong
- Dao dong dien t u dieu hoa xay ra trong mach LC sau khi tu dien dugc tich mot dien luong qo va khong co tac dung di^n t u ben ngoai len mach Do la
dao dong di^n t u t u do voi tan so' co = J —
•N/LC
c Bien thien di^t tich va ddng dien trong mach dao dong
- Dien tich tren tu bien thien dieu hoa voi phuong trinh: q = qQ.cos((ot + cp)
Trong do:
Tan so'goc ciia mach dao dpng o) = J —
v LC Chu ki rieng cua mach dao dpng T = — = - = InyfCc
O) f
Tan so'dao dong rieng ciia mach ( = — = — = — L _
• ^ ^ • 2;: T inyflC
- Cuong dp dong dien: i = q' = -qo(osin(a)t + cp) = I()Cos(cot + + ^ ) ;
IJlj^ Trong do I(, =
- Hi?u di^n the giiia hai ban tu: u = ^ = ^.cos(cot + (p) = UoCos(cot + (p),
Voi UQ = ^ Cuong dp dong difn qua L va hi^u dien thegiira hai ban ty bien j^thien dieu hoa cung tan so goc voi dien tich cua tu di^n
^jP^ - u va q cung pha nhung l^ch pha ^ so voi i
d Nang lucntg difn tie trong mach dao dgng
- Tong nang lupng dien truong tren tu di?n va nang luong tir truong tren cuon cam gpi la nang lupng dien tir
2 '
Nang lupng dien truong tap trung 6 ty di?n: W j = ^ ' ^ ^ ^ ^ {^^ ^ )
, 231
Trang 37- Nang lu<?ng tir truang tap trung a cupn cam: Wj = ^ s i n ^ (cot + cp)
- Trong qua trinh dao dgng difn tir c6 su chuyen hoa qua lai giCra nang
lugng dien va nang lugng tu ciia mach Nang lugng dien va nang lugng tu
bien thien haan hoan theo thoi gian voi tan so goc la co' = 2co, chu ki la T/2, tan
so dao dong la 2f; tong cua chiing la nang lugng toan phan ciia mach (nang
lugng dien tir) c6 gia tri khong doi .^^,
- Trong mach LC c6 di^n tro thuan R la dang ke thi c6 su toa nhiet do hien
ung Jun - Lenxo nen nang lugng toan phan giam theo thai gian, bien dg dao
dong cung giam theo va dao dong tat dan Ne'u di?n tro R ciia m^ch nho, thi
dao dong coi gan dung la tuan hoan voi tan so goc w = ^^i—
- Di^n tro tang thi dao dong tat nhanh, va khi dien tro vugt qua mot gia trj
nao do, thi qua trinh bien doi trong mach phi tuan hoan
- Ne'u bang mot co che thich hgp dua them nang lugng vao mach trong timg
chu ky bu lai dugc nang lugng tieu hao thi dao dgng ciia mach dugc duy tri
e) Su tuong tugiiia dao dong co vd dao dong dim
Dai lugng bien
thien
Li dg X
Van toe V = x' Gia toe a = v ' = x "
Di^n tich ciia ty q Cuong dg dong di^n i = q' Hieu di^n the'u
Tan so' dao
Xac nhan tao dao dgng cuong buc pieu kien cgng huc^ng
Lye can sinh cong am
Ngoai lye tuan hoan
F = Fo cos (ci)t + cj))
CO = (i)o Hay f = fo
Di#n tro R lam toa nhi^t
Hi^u di^n the
u = Uo cos (cot + (p)
CO = coo Hay f = fo
,-vh
Ta thay:
Hai loai dao dgng CO ban chat khac nhau
- Nhung giiia chiing CO su tuong tu: !>• v«
X q; V i ; m <-> L; k <-> 1/C;
2, Difn tir truong
a) Gia thuyei Maxwell
- Tu truong bien thien theo thoi gian thi sinh ra mot dien truong xoay
- Di^n truong bien thien theo thoi gian thi sinh ra tu truong
b) Ddng dien dich
- Dong dien dan: la dong chuyen doi co huong ciia eac hat mang di?n
- Dong dien djch: sinh ra o khoang giira hai ban tii dien khi di^n truang ciia ty bien thien Trong mach dien LC, dong di^n dugc khep kin 6 eac doan
day noi va cugn cam ha'\g dien dan va dong dien dich giira hai ban tu
di?n Dong diC^n djch la mgt khai niem de bieu thi su bien thien eiia di^n trirong; no tuong duang nhu mgt dong dien
^) Di^n tit truong
Tir gia thuye't Maxwell, moi bien thien theo thoi gian ciia tu truang deu
"'nh ra trong khong gian xung quanh mgt di§n truong xoay bien thien theo thai gian va nguge lai moi bien thien theo thai gian ciia mgt di^n truang cung
l " ! ^ ra mgt tu truong bien thien theo thai gian trong khong gian xung quanh
•^Lr truong va dien truang bien thien theo thai gian va khong ton tai rieng biet,
9c lap voi nhau, ma chi la bieu hi^n ciia mgt truong tong quat, duy nhat, ggi
^^Hn tiftrimng "
ti^r truyen di trong khong gian ciia eiia di?n tu truang bien
dieu hoa theo thoi gian •
'ill
^ Songdi^ntu
^inhnghia
Trang 38b Dac diem song dien tit
- Song d i ^ n t u Ian truyen dugc trong m o i t r u o n g vat chat va troi,,
chan k h o n g
- Song d i ^ n t u la song ngang cac vecto E va B vuong goc voi nhau
vuong goc v o i p h u o n g truyen song ' « i
- Dao dpng ciia dien truong va t u truong tai 1 diem luon dong pha
- Song dien t u c6 day d u tinh chat n h u song co hoc: phan xa, khuc xa, gjg^
thoa, nhieu xa
- Song dien t u mang nang lugng ti voi luy thiia bac 4 ciia tan so
c Song v6 tuyen
Song dien t u c6 buoc song t u vai m den vai k m d u n g trong thong tin vo
tuyen gpi la song v6 tuyen
- Song dai (buoc song t u 1000m den 100km) it bj nuac hap thu nen
thuon-dupe dung de truyen thong tin d u o i nuoc
- Song trung (buoc song t u 100m den 1000m) ban ngay tang dien 11 h.Vp
thu, ban dem phan xa, nen ban dem truyen di dupe xa trong khong gian bin
tren mat da't
- Song ngan (buoc song t u 10m den 100m) c6 nang lupng Ion va dupe tnng
di?n l i va mat dat phan xa nhieu Ian nen truyen d i rat xa tren mat da't
- Song cue ngan (buoc song t u 0,01m den 10m) c6 nang lupng Ion, khong
bi tang dien li hap thu ma truyen thSng D u n g trong v6 tuyen tuyen hinh \
thong tin trong via t r y
Song dai I k m - l O k m 0 , l M H z - l M H z
Song trung lOOm-l.OOOm (1km) 1 M H z - 10 M H z
Song ngan lOm-lOOm 10 M H z - 100 M H z
Song cue ngan I m - l O m lOOMHz-lOOOMHz
4 S u thu va phat song di^n tir
- Ngui/cn tac chung ve^thong tin lien lac bang song vo tuyen
+ Phai diing song dien tu cao tan de tai thong tin gpi la song mang
+ Phai bien dieu cac song mang: " T r p n " song am tan v o i song mang
+ 6 noi thu phai tach song am tan ra khoi song mang
+ Khuc'ch dai tin hi^u thu dupe
- So do khoi mot may phat thanh:
+ Micro, bp phat song cao tan, mach bien d i ^ u , mach khuech dai va ^
ten
Sa do khoi mot may thu thanh:
+ Anten, mach khuech dai dao dpng dien t u cao tan, mach tach song,
^gch khuech dai dao dong dien t u am tan va loa
May phat hay thu song dien tir: chi phat hay thu s6ng di?n t u c6 tan so
bang tan so rieng cua mach dao dpng LC la f = L _ •
C la dien dung cua bp tu dien
Ne'u bp tu gom C, C2, G, mSc noi tiep, d i f n dung cua bp ty tinh boi
1 1 1 + — + — + .,•
Trang 39^' -> K h i d i i n g hai tu C, va C 2 mic song song, di^n d u n g cua bp t y C - C, + G
Suy ra tan so: -y^^i 'a "
Vly TNHHMTV DWH Khang Vi$t
y i dv 1: Mach dao dong L C c6 cupn day thuan cam v o l dp \yt cam
I = i l O ~ ^ H , t u di?n c6 dien d u n g C = —|iF Bo qua di?n t r o day noi Tan
SO dao dpng di#n tir t y do cua mach la
Vol L = - 1 0 ' ' H , C = - n F = F ,
Thay so vao ta dupe dpng: f = ^ = 5000Hz
H Q - 2 2Q-6 fj !f(>b t i li.'i , 2.71 J —
V 7C 7t
L u u y:
- Dap an A sai do cong thuc tinh f da d i i n g n h u n g k h i thay so chua doi don v i ciia C
- Dap an B sai la do n h a m v o i bieu thuc tinh chu k i
- Dap an C sai la do nham vai bieu thuc tinh chu k i va chua doi don v i cua C
= > C h p n D
V i 2: M p t mach dao dpng LC c6 tu di^n C = 0 , 2 m F , cupn day thuan
cam Lay 71^ = 10 De mach c6 tan so'dao dpng rieng 500Hz t h i h$ so'tu cam
L phai CO gia t r j bang
rnpt tu di^n c6 dien d u n g C Fan so dao dpng rieng ciia mach la I M H z
"^ia trj ciia C bang:
A C = — p F B C = — F C C = - - m F D C = — ^ F
47: 47t 471 4 ; i
Trang 40Huong dan gidi:
Vi dy 4: Cho mach dao dong dien tu LC ly tuong Nguoi ta giu nguyen do
tu cam cua cuon day va dieu chinh de dien dung ciia tu dien tang len 4 Ian
thi chu ki dao dong rieng cua mach thay doi nhu thenao?
A Tang 4 Ian B Giam 4 Ian C Giam 2 Ian D Tang 2 Ian
Hu&ng dan gidi:
Chu ki dao dong rieng khi chua tang C:
T = 2 T I V L C
Chu ki dao dong rieng khi tang C len 4 Ian:
T' = 2KN/L.4C = 2(27iN/Lr) = 2T ^- '
Vay chu ki tang 2 Ian Chon D
Vi du 5: Cho mach dao dong dien tu LC ly tuong Neu tang dien dung cua
mach dao dong len 8 Ian, dong thoi giam do tu cam cua cuon day di 2 lain thi
tan so dao dQng rieng cua mach tang hay giam bao nhieu Ian?
A Tang 4 Ian B Giam 4 Ian
C Giam 2 Ian D Tang 2 Ian
Huang dan gidi:
Tan so giam di hai Ian -> Chon C
Vi du 6: Mot mach dao dong gom c6 mpt cupn cam c6 do tu cam L = lO'^H
va mot tu dien c6 dien dung dieu chinh duoc trong khoang tu 4pF den
400pF (IpF = 10'2F).Mach nay c6 the c6 nhCrng tan so rieng nhu thenao?
LMW y: Voi each suy luan nhu tren thi rat chat che nhung su bieh doi ha^
tiic la tan so bieh doi tu 2,52.10'^Hz den 2,52.10''Hz
Vi du 7: Mot mach dao dong gom cuon day L va tu dien C Neu dung tu Ci thi tan so dao dong rieng cua mach la 60kHz, neu dung tu C 2 thi tan so dao dpng rieng la 80kHz Neu hai tu Ci va C 2 m3c song song thi tan so dao dong
rieng cua mach la
^png rieng la 80kHz Neu hai tu Ci va C 2 mic nol tiep thi tan so dao dong
rieng ciia mach la ^
_ A 100kHz B 140kHz C 20kHz D 48kHz
Huang dan gidi:
'Tac6:f;?t = f f + < f =^ ^nt =100kHz
=> Chon A