Vấn đề 4 : sóng cơ học - giao thoa ánh sáng - sóng dừng doc

A
C
B
I
D
G
H
F
E
J





λ


λ



 





!"#$%&'(&)*+,,+$%)$%-
* ./01/23


4)56123
λ
47&8)90:


 
 
λ
λ
 
= = =
 
 
3#;<4
6
** =>?1@ABAA"CDEA"=FG11AD=/"EHF/1ID=/@/
2
   

ω π
ϕ
λ
 
∆ = =
 
 
3#;J4


ϕ π

∆ =
  !"#$%&'()
[ ]
 
λ
⇒ =
"*
 ∈
3#;K4

+ ,
ϕ π
∆ = +
 !"#$%-&()

( )

 
 
  
λ
λ
 
 
⇒ = + = +
 ÷
 
 
 
"*

 ∈
3#;#4

+ ,


π
ϕ
∆ = +
 !"#$%".()

( )

 
  /
  
λ λ
 
 
⇒ = + = +
 ÷
 
 
 
"*
 ∈
3#;L4
*** /2/"CDEA"=MF11N2+D=/">GE
<
GE

J

012(3&3)
[ ]
4 4
 $+  ,  
ω ϕ
= +
⇒
 !"#$ %&'

4 4
 
 $+  ,  $+  ,
"

       
π
ω ϕ ϕ π ϕ
λ
 
= + − ∆ = + −
 
 
3#;O4
&PQ()*!+ '
+
H+;13R/ST
+
4

 *!",(-+ '






π
π ϕ
λ
π
π ϕ
λ

 
= + +
 ÷

  

 

= + −
 ÷

 

os
os
F +

 +
E
 +;1 : ;/
E
 +;1 : ;/
Mt s đim cn ch  khi gii ton:
G>?>G==7&/U1GD=/0@@@V/ ./WQ<J7 A<
56$1&7&8 !&'(
9:;<=#!%>?=@9*&
56$1&7&8 !-&(
9:;<=#!%>=A29*&

&$
B4CDE
FCE

G

<;./+01/+ 2/345#6789/&:
;</=>+?
@A'BCDE,F5CGH,I5
J;J:</=>+K:L2M+,2L<2L@9"=>?1@A
BAAEA"=;?
K;NO P*Q/+16RS

:4@*T?
#;UVP9/LWRS,W9XW?
L;@RY+7*0<S>!TLW?Z/
LW/,RY-[#1YT 


[&?
O;N/ L*\9?(\9!L*:LP>%0 +02*
!?Z]^ \9<L1?
X;Z_L*+,2L*`WL/ (aW03<L02*
!LV:L?Y/0/,<)02*
W[%^#Q(aW[&?
* *+,,+$%
  &PQ
YZ/[1B"CD12"=1\1">G"//\11]A+5G^"@>
/_`/.+M5>GD/"CD;
YZ/[1B"CD12"=1\1/C>G^"@>"U/`/.+M5>GD/
"CDMaDb8c6B@>1\1"
YdV11BAAeAAP/2>/f@AagA612;
• Giao thoa – Điều kiện đ có giao thoa:
 Hb=[9+T)9+W,KcL02
**#[9+&=!=:?
 de>9P]<%/)9+?J/
M1Y*>+
TfW[_?
<; ANEA"=1I@A3h//\11]AAN+M5>G
EhEA"=1\1"4
012(&I"#G$%&'
()
[ ]
 $+  ,  $+  ,
 g
      
ω π
= = =
JK3 !&7&!%;$1


 "=
C&7&G!%;$1

 g"=
3;L*)


 
 $+  ,
 "

    
π
π
λ
→
 
⇒ = −
 
 
G>?>G==7&/U1GD=/0@@@V/ ./WQ<J7 AJ
 G


λ
G




G


λ

λ

3;LG*)


 
 $+  ,
g "

    
π
π
λ
→
 
⇒ = −
 
 
A4 /2/ij@/"CDFEAN2+G5//6
   
  $ + , $   + ,
"  " g "
           
π π
π

λ λ
→ →
 
 
⇒ = + = − − +
 
 
 
 

+/M,
4 5"=1]A2/ij@/F
 
 

 
∆
= = −
 
 
F
+ +; 1 +; 1 3 E E 4
ϕ π
λ
+/D,
14 =>?1@A1]AA2/"CDF

   

3 E E 4 3 E E 4


ω π
ϕ
λ
 
∆ = − = −
 
 
6
 
∈
3#;k4
  &PQ
CDEA"=1\1"+
DAb
HJ+
 


 
∆ = − =
 
 
3 E E 4 8
π
ϕ π
λ

[ ]
 

⇒ − =E E 8
λ
6
 
∈
3#;<l4
⇒
Tại những đim này hai dao đng thành phn cùng pha và biên đ dao đng của sóng tổng hợp
cực đại.( h@>/C?a`/>/c)
CDEA"=1\1/C+
D
Hl 
 

 
 
∆ = − = +
 
 
3 E E 4 3 8 4
π
ϕ π
λ

 

 
 
⇒ − = + = +E E 3 8 4 3 8 4
λ

λ
6
 
∈
3#;<<4
⇒
Tại những đim này hai dao đng thành phn ngược pha và biên đ dao đng của sóng tổng hợp
cực tiu.( h@>/C?a`/"U//c).
∗ h"CDEA"=/=1"//\1Tg:L*%"=1\1"V
1\1"//mDQ%8Hl
⇒
A=!0RE'
 = ±
?A=!0R'
 = ±
[Ee'@X=!0RI'
D
= ±
BZW=:XL2'
⇒
A=:0RE'
4N  = −
?A=:0R'
N  = − −
[Ee'@X=:0RI'
MN D = −
E4 Fn$op,q rs'q*t*
DẠNG 1: G;$1&7&L !*=@=-=#

C


O3$%"*9?% &P&308
"*QP&&IG&R&P&3;7&O!"$S&T+9#U&$!%$3=-,
@@
SJ7&V9W&6&IR&P&33)
d
XB
BY(Z&.[&&$ !$%&P&3)

 

E E d d ;; d
:
λ
− = = =
B\3=-&@!)"$S&T
DẠNG 2: G;$1&7&L !*=@=-=#

C

J7&V]&:&I !$%
^$9
λ
$S&""#T
@@
B_W(`>)
 
E E

ε

λ
−
= +
O$)=#(@?N
ε
=#(@W((a
G>?>G==7&/U1GD=/0@@@V/ ./WQ<J7 AK

B
4
ε
=
=# !%&R$%cực đạiBậc K= n
B
4 bM
ε
=
=# !%&R$%cực tiuBậc n + 1
DẠNG 3: G%=c&(&I&'* !?&'!%(;$1&7&
L !*=@=-=#

C

J7&V;$1&7&$S&
λ
C""#T
@@
B\2Z&.[&)
( )
( )

 
 

; E E
; E E 3 4

 
−
∆ = − = ∗
 
 
ω
π
ϕ
λ
7 $%&'(
d
ϕ π
∆ =
"#$
3 4∗
⇒
3=-&@!
7$%-&(
( )
 d
ϕ π
∆ = +
"#$
3 4∗

⇒
3=-&@!
7$%".(
( )
 

d
π
ϕ
∆ = +
"#$
3 4∗
⇒
3=-&@!
&PQ)
7dV11BAAe3"CDEA"=1\1"4AAP/3"CDEA"=1\1/C42>/f@
AagA612

> 
λ
=
DẠNG 4: J7&V"V]"#> !$%&P&3?$3G+d*"#G=#,
@@
B0e=# !$%&P&3?$3G"#&7&CG=@=-8$3

C

O&)
 


 
 
E E d
+5 d
E 3 4
E E +5
λ
λ
+ =

 
⇒ = + ∗

 
+ =
 

Bf$

4 E +5≤ ≤
6-("*
3 4∗
\)
+5 +5
d
λ λ
 
− ≤ ≤
 
 


3 4∗ ∗
"*
d u∈
  &PQ)
• ^7& !$%&P&3?$3G+]&1 !"#G"#G=# !$%&P&3,
&]=#7g&7&7V6h!R&.[&
3 4∗ ∗
• dV]&7& !$%&P&3i7&V9j&.[&
3 4∗
DẠNG 5: J7&V"V]"#> !$%&P& ?$3G+d*"#G=#,
@@
B0e=# !$%&P& ?$3G"#&7&CG=@=-8$3

C

O&)
 

 

 

 /
E E d
+5
E 3 d 4 3 4
E E +5
λ
λ


 
+ = +

 
 ÷
⇒ = + + ∗
 

 
 

+ =

Bf$

4 E +5≤ ≤
6-("*
3 4∗
\)
 
 
+5 +5
d
λ λ
 
− − ≤ ≤ −
 
 


3 4∗ ∗
"*
d u∈
  &PQ)
• ^7& !$%&P& ?$3G&]=#7g&7&7V6h!R&.[&
3 4∗ ∗
• dV]&7& !$%&P& i7&V9j&.[&
3 4∗
• &2/CEI1/U1A311J4"CVE#GEL
&1Jfb1"v0"CDEA"=1\1"G1\1/C/"+5
aR+PY+Xh!'
G>?>G==7&/U1GD=/0@@@V/ ./WQ<J7 A#

 
= +
 
 
g
 i
λ
"2@9#"*

 (∈
,NJ@9/.@@m
GUY:L*1\1"2!`g'#WYj&
[ ]
 ; +
3fwHl/A"CD+M5>GA"CDEA"=1\1"4
SUY:L*1\1/C2!`g#WYk&
[ ]

[ ]
4 b
  4 b
M ;
; w M

<


+ ≥


2n neáu X
neáu
&PQfb1"v0"CDEA"=1\1"G1\1/C/8V+5
B$0EA"=1\1")
 J;)<3fwHl4
 J;S<3fw
≠
l4
S$0"CDEA"=1\1/C/\/
[ ]
[ ]
4 b
  4 b
M ;
; w M

<



+ ≥


2n neáu X
neáu
J; AEA"=j1@A3h//\11]AAN+M5>GEhEA"=1\1/C4
+  , +  ,N
ω π
= =

     
"#
+  , +  ,N
ω π π π
= + = +
g
     
A4 5"=1]A2/ij@
   
 

+ A;  3E E 4 A; 1 3 E E 4
π π π
λ λ
 
 
= − = − +
 
 

 
 
3#;<J4
4 CDEA"=1\1"
 

 
 
E E 3 8 4 3 8 4
λ
λ
 
− = + = +
 
 
3#;<K4
14 CDEA"=1\1/C
[ ]
 
E E 8
λ
− =
3#;<#4
E4 $0"CDEA"=1\1"G1\1/Cj1b1"vj1>6111/U18ANEA
"=1I@A
K; AEA"=@A
+  , +  ,N
ω π
= =


     
"#
+  , +  ,N
 
π π
ω π
= + = +
g
     
A4 5"=1]A2/ij@
   
 
/ /
+ A;  3E E 4 A; 1 3 E E 4
π π π π
λ λ
 
   
= − − = − +
 
   
   
 
3#;<L4
4 CDEA"=1\1"
 
/
E E 8
λ
λ

 
− = +
 
 
3#;<K4
14 CDEA"=1\1/C
( )
 
 
 /
E E 8
λ λ
 
− = + +
 
 
3#;<O4
E4 $0"CDEA"1\1"a60"CDEA"=1\1/C
 
/ /
+5 +5
d− − ≤ ≤ −
λ λ
3#;<X4
$%
-
H\L=#c-$$8*"#(1i3?&'!%"W#3$#
G>?>G==7&/U1GD=/0@@@V/ ./WQ<J7 AL
YdV11BAAex1AP/>/f@AagA612;
YdV11BAD=/eGD=/P/>/f@Aa<y#612;

/
λ
λ
G

%@&>V

λ

λ
G

%@9V;]kl9*& m@9V;]k9*& @nko9*&

8"V]&>V&9?%$%&P&3+9Z,"#8 !;.$%+p,
_q)
B\L&r-& =#&&7&p"#&7&9Z10"v/8A
B0*310"v⇒ P/2 B0*3/\E⇒ 5e2
BN(7⇒ -&&$@p=#P/2
BG%9Z/+"*=#9?%$%&I,
<; A"9Em10"v)
A4 Điều kiện về chiều dài
 g=
của dây có sóng dừng)

  
; 
+5 >   ;
:
 

= = = =
 
 
λ
"*

 (∈
3#;<L4
4 S nt và s bụng sóng)
 e:Lf)\>p>9Z!%$"V
B\>9ZX>9X
B\>pXB
 e:L07)\>9Z>p!%$"V
B\>9?XF
B\>9ZXB
B\>pX
 F=/"910"vD=/"9/\E\>9ZX>p
A4 Điều kiện về chiều dài
 g
=
của dây có sóng dừng)
( )
 
/  /
λ λ λ
= = + = ++5 >  
"*

 (∈
+/s,


/
λ
= D
"*m = 1, 3, 5, 7…
4 S nt và s bụng sóng)
B\>9?X
B\>9ZX>pXB
Mt s đim cn ch  khi gii ton:
<; .:67/><V:</l l=S
L*9+TV?
J; ./1Y3T9X/f,1WY3#=&07?
K; Ulm]<n/Y/%*02T/+X6h?Z,1Y
/n9071Y/hf%!S -2?
G>?>G==7&/U1GD=/0@@@V/ ./WQ<J7 AO
m@&>V