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Chng 9. SNG C
Sng bt u t gi ?
+ Sng ngang:
+ Sng dc l sng c phng dao ng ca cc
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1. Mt s khi nim c bn
Bi 1. CC C TRNG CA SNG
+ Sng c l nhng dao ng c lan truyn trong mi trng n hi.
+ Ch : Khi mt sng truyn qua mi trng th cc
phn t ca mi trng khng chuyn ng cng sng.
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+ Mt sng: qu tch nhng im cng gi tr pha dao ng.
+ Mt u sng: mt sng gii hn gia phn mi trng sng truyn qua v phn mi trng sng sp truyn ti.
Sng cu Sng phng
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2. Cc c trng ca sng
+ Bc sng(): l khong cch gia hai im gn nhau nh
t trn phng truyn sng m dao ng ti hai im l c
ng pha.+ Chu k (T) v tn s (f) ca sng l chu k v tn s c
a cc phn t dao ng ca mi trng.
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+ Vn tc sng (v): l vn tc truyn pha dao ng
v fT
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3. Phng trnh truyn sng c
+ Xt sng phng, truyn theo phng Ox, trong mitrng ng cht v ng hng.
+ Ti O: cosou a t
+ Ti M: cos cos 2Md d
u a t a tv
2
.
di t
u a e
Vit di dng s phc c:
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Bi 2. S GIAO THOA SNG
+ Xt 2 ngun sng O1 v O2
c cng tn s, bin .
1 1os t + u ac
1 1;MO d 2 2MO d
2 2os t +u ac
1. Hin tng giao thoa sng c
O1
O2
d1
d2
M
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- Sng do O1 truyn ti :
- Sng do O2 truyn ti :
11 1os t + - 2
M
du ac
22 2os t + - 2
M
du ac
+ Ti M trong min truyn ca 2 sng:
+ Sng tng hp ti M:1 2M M Mu u u
1 2 2 12 1 2 12 os os t 2 2
Mu ac d d c d d
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1 22 12 os2
A a c d d
+ Bin sng tng hp ti M:
+ Nhn xt : Trng hp 2 ngun cng pha:
- A max khi: 1 2d d k
- A min khi: 1 2
1
2d d k
0, 1, 2,...k
1 2 0
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+ Nhn xt : Trng hp 2 ngun ngc pha:
- A max khi:
1 2d d k - A min khi:
1 2
1
2d d k
0, 1, 2,...k
1 2
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+ L hin tng giao thoa ca 2 sng phng cng bin ,
cng phng truyn nhng ngc chiu.
2. Sng dng
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Ti thi im t=0 v t=T/2 ton
b si dy u ng yn tc th
i.
Hnh nh sng dng trn dy
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os t - 2OMd
u ac
os t + 2OBMd
u ac
O M B
d
+ Sng ti:
+ Sng phn x:
+ Sng tng hp ti M: 2 os 2 . os tMd
u ac c
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+ Bin A ca sng tng hp: 2 os 2d
A ac
2d k
- A max khi:
- A min khi: 2 14
d k
vi k = 0, 1, 2,
Bng sng: l nhng phn t ca mi trng dao ng
vi bin cc i
Nt sng: l nhng phn t ca mi trng dao ng
vi bin bng khng (khng dao ng)
vi k = 0, 1, 2,
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Khong cch gia 2 bng (hoc 2 nt)
lin k l: /2
Bi 3. HIN TNG NHIU X SNG C
1. Nguyn l Huygens
+ Bt k mt im no nhn c sng truyn n u
tr thnh ngun sng th cp
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2. Hin tng nhiu x sng c
+ L hin tng cc tia sng i phng truyn
khi i qua cc chng ngi vt.
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/ 1d / 1d
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N TP
9.1
9.2
9.8
9.11
9.14
9.15
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