mechanical wave

Chng 9. SNG C

Sng bt u t gi ?

+ Sng ngang:

+ Sng dc l sng c phng dao ng ca cc

http:// www.truongvatly.blogspot.com Copyright Trng Vt L

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.


+ 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


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.


+ Vn tc sng (v): l vn tc truyn pha dao ng

v fT


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:


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


- 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


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


+ 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


+ L hin tng giao thoa ca 2 sng phng cng bin ,

cng phng truyn nhng ngc chiu.

2. Sng dng


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


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


+ 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,



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


2. Hin tng nhiu x sng c

+ L hin tng cc tia sng i phng truyn

khi i qua cc chng ngi vt.


/ 1d / 1d


N TP

9.1

9.2

9.8

9.11

9.14

9.15


mechanical wave

Documents