Phương pháp giải nhanh trắc nghiệm vật lý 12

Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 1




oOo


SÁNG KIN - KINH NGHIM


TÊN  TÀI:



PHNG PHÁP,
TH THẠT GII NHANH
CÁC DNG TRC NGHIM
ạT LÝ 12

NgỀyn Trn Cng
Trng THPT ẮhỀyên Lê QỀý ôn






Quy Nhn, tháng 5/2010
www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 2
TÊN  TÀI:
PHNG PHÁP, TH THẠT GII NHANH CÁC DNG
TRC NGHIM ạT LÝ 12

A. M Ạ
1. LỦ do chn đ tài:














không quá 1,5 phút

và các công


trình.
2. Nhim v ca đ tài ậ Gii hn đ tài.
Ậ. Nhim ề ẮẬ ơ ếài:
 




ậ. Gii hn ơ ếài:

 
+ 

Ắ. Hng phốế ếrin ơ ếài:


 

3. Phng pháp tin hành.




giáo khoa.
4. C s và thi gian tin hành nghiên cu đ tài.

 
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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 3

MC LC
Trang
A. M U
 01
   01
nh. 01
 01
B. NI DUNG
PHN MT: NG TRÒN LNG GIÁC
 02
 02
 03
 06
 08
 09
PHN HAI: TNG HP DAO NG IẠ HÒA
 10
 10
 11
 12
 14

 14
PHN BA: GIAO THOA SÓNG C
 15
 15
 16
 19
 21
 21
 22
C. KT LUN
 23
 23
 23


TÀI LIU THAM KHO


.
 - 
.
 
.
T 



www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 4


PHN MT
NG TRÒN LNG GIÁC

1. Mô t tình trng s vic hin ti :





       
 


x = Acos(t + 
               
=Acos(t+
1


2


* Nhn ếhy mế s nhẮ ơim ẮẬ phng phốp này khi làm ếrẮ nghim:

t + ) m
- Asin(t + i a = -
2
Acos(t + ). Lúc
                tròn

 (v),



/2




    
l                


 


2. Mô t ni dung gii pháp mi :
Ậ. C s lỜ ếhỀyế :


+ (t + 
x
)
+ -

Asin(t + 
x
)
- 
2

Acos(t + 
x
)
ậ. Gii phốp mi:



os(t +
x

) là hàm cosin

max
= A
O
a
x
v
I
II
IV
III
x


V


a


1
2
3
4
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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 5


= - Asin(t + 
x

               
V
max
=
A


Acos(t + 
V

/2
vx
  





= - 
2
Acos(t + 
x
) = -
2



max
=
2

A

2
Acos(t + 
a

/2
a x v
    
   





sau :
+ Bn ơim ơẮ ậiế:

- 
( x
max
= A ; v = 0 ; a = -
2

A)

- 
( x = 0 ; v = -
A

; a = 0 )

- 
( x = -A ; v = 0 ; a
max
=
2

A )

- 
( x = 0 ; V
max
=
A

; a = 0)


 



+ Bn ềủng ơẮ ậiế:
Vùng 1: x>0 ; v<0 , a<0
u (-

Vùng 2: x<0 ; v<0 , a>0
     -        

Vùng 3: x<0 ; v>0 , a>0
 

Vùng 4: x>0 ; v>0 , a<0
    

+ Mi qỀẬn h ề phẬ ẮẬ li ơ (x), ền ếẮ (ề), giẬ ếẮ (Ậ):


/2
vx
  

và
/2
a x v
    
   


/2


/2


 góc
/2




a
x
v
O
I
II
IV
III
1
2
3
4
www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 6
3. Chng minh tính kh thi ca gii pháp mi:
             


 

Câu 01



A. v = 0cm/s. B. v = 75,4cm/s. C. v = - 75,4cm/s. D. v = 6cm/s.
Gii:

    
 
t

=2

.7,5 = 15

   


Câu 02.       


t +
/2



A. a = 0cm/s

2
B. a = 946,5cm/s
2
.
C. a = - 946,5cm/s
2
D. a = - 946,5cm/s.
Gii:




góc
t

= 4

.5 = 20


-
2
A

= - 947,5cm/s
2

Câu 03.             
v=10


cos(2

t +
/2


A. x = 1,5cm.
B. x = - 5cm. C. x= + 5cm. D. x = 0cm.
Gii:

quay 1 góc
t

=2

.1,5 = 3


- 
Câu 04: 
    
2cos(0,5t   
          

A. 8/3s
B. 2/3s
C. 2s D. 4/3s
Gii:

            


=
0,5

. t =


 

Câu 05. 
  

      
3
cm theo  

A. v = 4cos(3

t -
/3

)cm./s
B. v = 4

cos(

t +
/3

)cm./s

C. v = 4cos(3

t +
/6

)cm/s.
O
a
x
v
I
II
IV
III
Hình 1
O
a
x
v
I
II
IV
III
V
VI


Hình 2
O
a

x
v
I
II
IV
III
Hình 3
V
/3


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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 7
D. v = 4

cos(

t -
/6

)cm/s
Gii:

là +
/3

, 

A = 4




=> hàm v = 4

cos(

t +
/3

)cm./s , 
Câu 06: cos(0,5t-/6) cm/s.


A. 6s B. 2s C. 4/3s D. 14/3s
Gii:

           
V
max
=A

=2





Câu 07:        
    

t (cm/s
2

10 m/s
2


A. 5N B. 1 N
C. 5,5N D. 
Gii:
     



=> F = k

l
0
= mg = 5 N
Câu 08: 

= 10 m/s
2
      
      


cos(5t - 2

A. 1/30s B. 11/30s C. 1/25s D. 1/10s

Gii:

giãn
0
2
4( )
mg g
l cm
k

   
      
    -    

=> góc quay 5

.t =
/2


Câu 09: 
  
5 /6 0,5 t


     
         
     
3
    



O
a
x
v
I
II
IV
III
V
VI
/3


Hình 4

a
x
v
I
II
IV
III
Hình 6
VI
V
5 /6


O
a
x
v
I
II
IV
III
Hình 5
VI
V
/2

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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 8
A. 6(s) B. 3(s) C. 2/3(s) D. 4/3(s)
Gii:
              
0



x=4cos(
0,5 5 /6t


)

t


= 0,5

.t =

( vì 

Câu 10 :             
v=24

cos(4t+          
1
  

2
= 37/12 (s) là
A. 141cm B. 96cm C.234cm
D. 117cm
Gii:
      
         t
1
=
    
1
2
4
3



   
   
21
29
12
t t t   
s quay

29 2
49
12 3
  
  
   


=> s =18A+0,5A+1A=19,5x6 =117 (cm), 
4. Mt s vn đ liên quan và vn dng:
Ậ. ạn ơ liên qỀẬn:




S tng t giẬ ắẬo ơng Ắ ềà ắẬo ơng ơin t

i lng
Ắ
i lng
ơin t
DẬo ơng Ắ

DẬo ơng ơin t
x
q

2
x = 0

2
q = 0
v
i
k
m



1
LC



m
L
x = Acos(t + )
q= q
0
cos(t + )
k
1
C

-Asin(t+ )
-q
0
sin(t+)
F
u
2 2 2
()
v
Ax



2 2 2
0
()
i
qq



µ
R
F = -kx = -m
2
x
2
q
u L q

C



W


W
t
(W
L
)
W

=
1
2
mv
2
W
t
=
1
2
Li
2
W
t

W


(W
C
)
W
t
=
1
2
kx
2
W

=
2
2
q
C



C
)


L
)
O
a
x

v
I
II
IV
III
Hình 7
VI
V
/6


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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 9






+ Bn ơim ơẮ ậiế:
- 
max
= Q
0
; i = 0 ; u
L
= -
0
Q

C
= - L
2

Q
0
)
        

- = -
0
Q

; u
L
= 0 )
        

- -Q
0
; i = 0 ; u
L

max
=
0
Q
C
= L
2


Q
0
)
        

-  IV: ( q = 0 ; i
max
=
0
Q

; u
L
= 0)

              



+ Bn ềủng ơẮ ậiế:
Vùng 1: q>0, i<0, u
L
<0 
Vùng 2: q<0, i<0, u
L
>0 
Vùng 3: q<0, i>0, u
L
>0 

Vùng 4: q>0, i>0, u
L
<0 
+Mi qỀẬn h ề phẬ ẮẬ ơin ếỜẮh (q), Ắng ơ ắỢng ơin ếẮ ếhi (i), ơin
áp ếrên hẬi ơỀ ẮỀn ắồy (Ề
L
):


L
):
/2
iq
  

và
/2
L
u q i
    
   
.
 

C

/2


L


góc
/2

.

L


/2


ậ. Phn ắành Ắho hẮ sinh ền ắng, ếỜnh ếoốn ếr li :
Câu 01          

-4
s



A. 4,0.10
-4
s. B. 0,5.10
-4
s
. C. 1,0.10
-4
s. D. 2,0.10
-4
s.

.
Câu 02. 







A. 5

.10
-6
s. B. 2,5

.10
-6
s. C . 10

.10
-6
s. D. 10
-6
s.
u
L
O
q
i
I

II
IV
III
q


i


L
u


1
2
3
4
www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 10

Câu 03. 

0
.

A. t = 8.10
-5
(s). B. t = 4.10
-5

(s).
C. t = 2.10
-5
(s). D. t = 10
-5
(s).

Câu 04. 

4
t + 


A. t = 0,5.10
- 4
(s).
B. t = 10
- 4
/3

(s). C. t = 0,67.10
- 4
(s). D. t = 10
- 4
/6

(s).

Câu 05. 


W = 0,25.10
-3
 

A. u = 250 cos (25.10
6
t - /2)(V). B. u = 250 cos(25.10
6
t +)(V).
C. u = 250 cos (25.10
6
t)(V).
D. u = 220 cos (25.10
6
t)(V).

Câu 06. 

0

gian là lúc q = -
3
Q
0

A. q = 10
-4
cos (100t + /2)(C). B. q = 10
-4
cos (100t + /6)(C).

C. q = 0,01cos (1000t - /6) (mC). D. q = 0,1cos (1000t + 7/6)(mC)

Câu 07. in10
4
t(V),


F). 
A. i = 2.10
-2
cos (10
4
t ) (A) B. i = 2.10
2
sin(10
4
t +

) (A)
C. i = 2cos (10
4
t +

/2) (A) D. i = 0,02cos(10
4
t-

) (A)

Câu 08.  

trình q = Q
0
cos(7000t + 

A. 74,8 s B. 14,96  C. 112,22 s
D. 186,99s

Câu 09. 

 

A. 3,2mJ. B. 0,256mJ. C. 0,320mJ. D. 0,288mJ

Câu 10. 
0
sin(2ft + 
 
tiêu là
A. I
0
/2f (C). B. 2I
0
/f (C)
C. I
0
/f (C) D. I
0
/4f (C).

5. u đim:

giúp c
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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 11
Th nhế:  


Th hẬi: 


t
) nào


Th ậẬ:  





Th ế: 

              




6. Nhc đim và khc phc:
 



/2


                
12 1 2
  
  



C

/2




).

 
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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 12

PHN HAI
TNG HP DAO NG IẠ HOÀ IẠ HOÀ CÙNG PHNG,
CÙNG TN S
1. Mô t tình trng s vic hin ti :


x
1
= A
1
cos(t+
1
) và x
2
=A
2
cos(t + 
2
        
 t+).

2 2 2
1 2 1 2 2 1
2 os( )A A A AAc

   

và
1 1 2 2
1 1 2 2
sin sin
tan
os os
AA
Ac Ac








1
 
2

1

2
)
 
1
, x
2
cùng pha)  A
Max
= A
1
+ A
2
 
1
, x
2
 A
Min

= A
1
- A
2


 A
1
- A
2
 
1
+ A
2

1
= A
1
cos(t + 
1

x=Acos(t+ 
2
= A
2
cos(t + 
2
).

2 2 2

2 1 1 1
2 os( )A A A AAc

   

11
2
11
sin sin
tan
os os
AA
Ac Ac







1
 
2

1

2
)



1
= A
1
cos(t + 
1
, x
2
= A
2
cos(t + 
2

x = Acos(t + ).
Chi

1 1 2 2
os os os
x
A Ac Ac Ac
  
   
và
1 1 2 2
sin sin sin
y
A A A A
  
   

22

xy
A A A  
và
tan
y
x
A
A


 [
Min
, 
Max
]
 



* Nhn ếhy mế s nhẮ ơim ẮẬ phng phốp này khi làm ếrẮ nghim:

 
 
nhp mốy
giáo viên.


hay
2









=1 thì

=
/4


3 / 4






2. Mô t ni dung gii pháp mi :
Ậ. C s lý ếhỀyế:

 
osx Ac t




A



.

*
= Ae
j (
)t


vì các



www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 13
     
*
= Ae
j

trong máy tính CASIO fx- 570ES  

A


.



-180
0
<


180
0
hay


<




oà.
      


ậ. Gii phốp mi: (Các thao tác vi máy tính CASIO fx ậ 570ES )
 

A



32SHIFT MODE 


31SHIFT MODE 

Mode 
 Complex (ắng s phẮ)        CMPLX. Ta

2MODE


D thì 
 R 

SHIFT 3MODE


SHIFT 4MODE






 
SHIFT 
.
Ví d
 
6 os /3x c t



6 60

hay
6 /3




- 
 
6 SHIFT 60
 
6 60
.
- 
 
6 SHIFT ( :3)


 
6 /3


.
3. Chng minh tính kh thi ca gii pháp mi:
Ậ.  ếờm ắẬo ơng ếng hp ếẬ ếhẮ hin phỘp ếỜnh Ắng:
Câu 1: 
x
1
= a
2
.cos(


t+

/4)(cm), x
2
= a.cos(

t +

      

A. x = a
2
.sin(

t +2

/3)(cm) B. x = a.sin(

t +

/2)(cm)
C. x = 3a/2.sin(

t +

/4)(cm) D. x = 2a/3.sin(

t +


/6)(cm)
Gii:

2 45 + 1 180   
. H
1 90

Câu 2: Ba 
là x
1
= 4 cos(

t -

/6) (cm) , x
2
= 5cos(

t -

/2) cm và x
3
=3cos(20t+2

/3) (cm).

A. 4,82cm; -1,15 rad B. 5,82cm; -1,15 rad
C.4,20cm; 1,15 rad D.8,80cm; 1,15 rad
Gii:


4 / 6 5 / 2 3 2 / 3
  
       
. H
4.82 1,15 

www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 14
ậ.  ếờm ắẬo ơng ếhành phn ếẬ ếhẮ hin phỘp ếỜnh ếr:
Câu 3:              
x=5
2
cos(

t + 5


x
1
=A
1
cos(

t +

1
) x
2
=5cos(


t+


A.

1
= 2

/3 B.

1
=

/2 C.

1
=

/4 D.

1
=
3/


Gii:

5 2 5 /12 5 / 6


   
. 
5 2 / 3


 A
Câu 4:               
    
1
= 2
3
cos(2t + /3) cm, x
2
= 4cos(2t +/6) cm và
t - 

A. 8cm và - /2 . B. 6cm và /3. C. 8cm và /6 . D. 8cm và /2.
Gii:

6 /6 2 3 /3 4 / 6
  
      
. 
8 /2



* LỀ ý
:


a+bi
A



A



a + bi. 

- a + bi 
A


:
SHIFT 2 3 

 
 
8 SHIFT ( :3)


  
3i
    
A




SHIFT 2 3 

/3



- 
A


a + bi :
SHIFT 2 4 

ềỜ ắ:
 
8 SHIFT ( :3)


   
/3


     a+bi 
SHIFT 2 4 

3i


A



bài


4. Mt s vn đ liên quan và vn dng:
Ậ.ạn ơ liên qỀẬn:

máy tính CASIO fx ậ 570MS 
CASIO fx ậ 570ES    
CASIO fx ậ 570MS 


CASIO fx ậ 570ES
.
ậ. Phn ắành Ắho hẮ sinh ền ắng, ếỜnh ếoốn, ếr li:
Câu 01: 
 
1
=cos(2t + )(cm), x
2
=
3
.cos(2t -      

A.
x = 2.cos(2t - 2/3) (cm) B. x = 4.cos(2t + /3) (cm)
C. x = 2.cos(2t + /3) (cm) D. x = 4.cos(2t + 4/3) (cm)

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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12

  Trang 15
Câu 02:            
1
= 3cos(5

t
+

/2) (cm) và x
2
= 3cos( 5

t + 5

/6)(cm).  
A. x = 3 cos ( 5

t +

/3) (cm). B. x = 3 cos ( 5

t + 2

/3) (cm).
C. x= 2 3 cos ( 5

t + 2

/3) (cm). D. x = 4 cos ( 5


t +

/3) (cm)

Câu 03: 
x
1
=cos(10t+
/3

)(cm) và x
2
= 2cos(10t + )(cm). 
h
A. x = 2 cos(10t +
4
)(cm) B. x =
3
cos(10t +
56/
)(cm)
C. x = 2cos(10t +
2
)(cm) D. x = 2
3
cos(10t +
4
)(cm)

Câu 04: 


1
= - 4sin(

t ) và x
2
= 4
3
cos(


 
A. x
1
= 8cos(

t +

/6) cm B. x
1
= 8sin(

t -

/6) cm
C. x
1
= 8cos(

t -


/6) cm D. x
1
= 8sin(

t +

/6) cm

Câu 05: 

1
= 2.sin(10t - /3) (cm), x
2
= cos(10t + /6) (cm) (t
. Xá
A. 5 (cm/s) B. 20 (cm) C. 1 (cm/s)
D. 10 (cm/s)

Câu 06: 



  ,  




  . 







AB
= cos100t (V) 
BC
=
3cos(100t-

/2) (V). 
AC
.
A.
AC
Cos
u 2 2 (100 t)V
B.
 
AC
cosu 2 100 t /3 V  

C.
 
AC
osu 2c 100 t /3 V   
D.
 
AC

osu 2c 100 t /3 V  


Câu 07:           
       
  
1
x 2 3cos 2 t /3 cm  
,
  
2
x 4cos 2 t /6 cm   
và
  
3
x 8sin 2 t cm
         

A. 12
/3
(rad) B. 
/6
(rad)
C. 
/6
(rad) D. -
/6
(rad)

Câu 08: 


5 2 os(100 )
1
cti


(A);
8 3 os(100 2 /3)
2
i c t


(A)
và
3 5 os(100 2 /3)
3
i c t



A.
6,97 os(100 2,05)i c t


(A) B.
5,97 os(100 2,05)i c t


(A)
C.

6,97 os(100 1,09)i c t


(A) D.
5,97 os(100 1,09)i c t


(A)

Câu 09:  

 4  



 , 
 

: x
1
= 3sin(t + ) cm, x
2
= 3cost (cm), x
3
= 2sin(t + ) cm,
x
4
= 2cost (cm). 




 .

A.
25 cos( /4)xt


cm B.
5 2cos( /2)xt


cm
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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 16
C.
5cos( /2)xt


cm D.
5cos( /4)xt


cm

Câu 10:  

 4  




 , 
 





 x
1
= 3 cos
t

2
(cm), x
2
= 3
3
cos(
2
2


t
)(cm),
x
3
=6cos(
3
4

2


t
) (cm) , x
4
= 6cos(
3
2
2


t
)(cm). 


.
A. x=6cos(
3
4
2


t
)(cm) B. x = 6cos(
3
2
2



t
)(cm)
C. x = 12cos(
3
4
2


t
) (cm) D. x= 12cos(
3


t
)(cm)

5. u đim:
Th nhế: nhiỀ 
       tr s ật k   
-
           

phút
Th hẬi: 

Th ậẬ: Khi tính 


còn tính theo hàm tan



6. Nhc đim và khc phc:
  



           
iáo viên có
fx ậ 570ES 



1MODE
 



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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 17

PHN BA
GIAO THOA SÓNG C

1. Mô t tình trng s vic hin ti :

Ậ) HẬi ngỀn ắẬo ơng Ắủng phẬ, Ắủng ậiên ơ:

1
, S

2
cách nhau
l
1
, d
2


12
Acos(2 )u u u ft

  


1
1
Acos(2 2 )
M
d
u ft



và
2
2
Acos(2 2 )
M
d
u ft





u
M
= u
1M
+ u
2M


 
12
2 1 1 2
2
2
M
dd
dd

   
  

      




2 os

2
M
A Ac




-  
12
0, 1, 2, 3 d d k k

     

- không tính hẬi ngỀn):
ll
k

  

- 
 
12
0,5 0, 1, 2, 3 d d k k

      

- không tính hẬi ngỀn):
11
22
ll

k

    

ậ) NỀ hẬi ngỀn ắẬo ơng ếhành phn ngẮ phẬ nhẬỀ ếẬ m rng
thêm:
- 
1
 d
2
= (k+0,5)


0, 1, 2, 3 k    

- không tính hẬi ngỀn):
11
22
ll
k

    

- 
1
 d
2
= k
0, 1, 2, 3 k    

-không tính hẬi ngỀn):
ll
k

  

* Nhn ếhy mế s nhẮ ơim ẮẬ phng phốp này khi làm ếrẮ nghim:
    



chính xác.





2.Mô t ni dung gii pháp mi :
Ậ. C s lý ếhỀyế:

1
, S
2
cách nhau
ml
1
, d
2
.
+ 

1 1 1
A cos(2 )u ft


và
2 2 2
A cos(2 )u ft




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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 18
1
1 1 1
A cos(2 2 )
M
d
u ft
  

  
và
2
2 2 2
A cos(2 2 )
M
d
u ft

  

  

u
M
= u
1M
+ u
2M

ậ. Gii phốp mi:
u
M

M


 570ES  cá
1M
)
và (u
2M


- 
 
2 1 1 2
2
M M M

dd

   

      

21
  
  


 
12
()
2
M
dd



    
(2)


bài.

-
21
  
  


-
21M M M
  
  


- 
2 2 2
1 2 1 2 M
2 osA A A AAc

   



1M
, d
2M
, d
1N
, d
2N
.
d
M
= d
1M
- d
2M

; d
N
= d
1N
- d
2N
và gid
M
< d
N
Thì ta có:
d
M
<
 
12
()
2
M
dd



    
< d
N


3. Chng minh tính kh thi ca gii pháp mi:
:

Câu 01:

1
= a
1
cos(50t + /2) và
u
2
= a
2
cos(50t + 
  d
1
và d
2


A. d
1
- d
2
= 4k + 2 (cm) B. d
1
- d
2
= 4k + 1 (cm)
C. d
1
- d
2

= 4k - 1 (cm) D. d
1
- d
2
= 2k - 1 (cm)
Gii:

100
4( )
25
v
cm
f

  

 
12
()
2
M
dd



    
Vì M

2
M

k


=> (d
1
- d
2
) =
4
(2 /2) 4 1
2
kk


  
=>
Câu 02:
1
và S
2

 
1
= a
1
cos(50t + /2) và u
2
= a
2
cos(50



1
- PS
2
= 5 cm, QS
1
- QS
2
= 7

 
 
www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 19
Gii:

100
4( )
25
v
cm
f

  

 
12
2

M
dd



    

=>
2
.5 2
42
P


   
=2k


=>
2
.7 3 (2 1)
42
Q
k

  
     

Câu 03: 


1
= u
2
= acos(10t)

- 

- phía A - phía A
- phía B - phía B
Gii:

20
4( )
5
v
cm
f

  

 
12
2
M
dd



    

=>
2
.10 0 5 (2 1) 2
4
N
kk

  
       


1
> d
2
 C

Câu 04:

1
= acos(10t), u
2
= bcos(10t + 

A. 5 B. 6 C. 4 D. 3
Gii:

20
4( )
5
v

cm
f

  

 
12
()
2
M
dd



    


(2 1)
M
k

  
=>(d
1
-d
2
) =
 
4
(2 1) ) 4

2
kk


  

mà  AB < d
1
-d
2
< AB nên ta có -2,5 < k < 2,5 có 5  
Câu 05: 
trình u
1
= acos(4t), u
2
= bcos(4t +         

A. 7 B. 8
C. 6 D. 5
Gii:

12
6( )
2
v
cm
f

  


 
12
()
2
M
dd



    


2
M
k


=> (d
1
-d
2
) =
6
(2 ) 6 3
2
kk


  

mà  AB < d
1
-d
2
< AB nên ta có -
Câu 06:

1
= acos(40t), u
2
= bcos(40t + 
 sao

A. 7
B. 6 C. 5 D. 4
Gii:

40
2( )
20
v
cm
f

  

 
12
()

2
M
dd



    

www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 20

2
M
k


=> (d
1
-d
2
) =
2
(2 ) 2 1
2
kk


  

mà  AB/3

d
1
-d
2

AB/3 nên ta có -2

k




Câu 07: 

1
= acos(30t), u
2
= bcos(30t + /2).


A. 10 B. 11
C. 12 D. 13
Gii:

30
2( )
15
v

cm
f

  

 
12
()
2
M
dd



    



(2 1)
M
k

  

=> (d
1
-d
2
) =
 

2
(2 1) / 2) 2 0,5
2
kk


   
mà  12

d
1
- d
2

12
ta có -6,25

k

    


Câu 08:

1
= acos(8t), u
2
= bcos(8



A. 8 B. 9 C. 10 D. 11
Gii:

4
1( )
4
v
cm
f

  
.

 
12
()
2
M
dd



    

       
(2 1)
M
k

  

=> (d
1
-d
2
) =
 
1
(2 1) 0) 0,5
2
kk


   

mà  4

d
1
-d
2


4 nên ta có - 4,5

k


Câu 09:
là u

1
= acos(8t), u
2
= bcos(8t + 


A. 8 B. 9 C. 10 D. 11

c sóng
4
1( )
4
v
cm
f

  
.

 
12
()
2
M
dd



    


2
M
k



=> (d
1
-d
2
) =
1
(2 ) 0,5
2
kk


  
mà  4

d
1
-d
2


4 nên ta có -3,5

k


=>
10cm
A
B
C
D
8cm
6cm
10cm
A
B
C
D
8cm
6cm
www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 21

Câu 10: 
1
và S
2

1
= a
1
cos(90t)cm,
u

2
=a
2
cos(90t +  S
1
S
2

M 
1
-MS
2

 M'  
1
-
2
   


B. 180 cm/s, 
 

Xét (d
1
-d
2
) = MS
1
-MS

2
= 13,5 = n

và 
1
- d

2
) = 
1
-
2
= 21,5 = (n+2)


ta có: 2

=8 =>


4 45 180( / )f x cm s




 
2 1 1 2
2
M M M
dd


   

      

=>
2
.13,5 6,5 ( 0,5)
44
M
k

  
     

4. Mt s vn đ liên quan và vn dng:
Ậ.ạn ơ liên qỀẬn:




   


   “ Ti ề ếrỜ ẮẬ ngỀn ếrong hin ếng
giẬo ếhoẬ (ềà sóng ắng) khợng ếh là ẮẮ ơi hẬy ẮẮ ếiỀ” 
+ 
trình sóng u
A
= u

B
= a.
+ 
2a, 









1

2


1
) // Ox qua M
2


2
       

2

2


M
1
.

1
M
3
ta
                
1


1

2


hòa)


A

M
3

M
2

M
1

x
1


u
2


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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 22
- AB <
 
12
()
2
M
dd



    
< AB => (khợng ếh ậng)

        “ xem nh
ngỀn rt gn ẮẮ tiỀ (tẮ là nỦt trong sóng ắng)

- AB


 
12
()
2
M
dd



    


AB =>
-AB


 
12
()
2
M
dd



    


AB


AB chia  

ậ.Phn ắành Ắho hẮ sinh ền ắng, ếỜnh ếoốn, ếr li :
Câu 01: 

A
= u
B
= 0,5 sin100

1
= 4,2 cm, d
2


A. k = 0. B. k =1. C. k =3.
D. k =2.

Câu 02: 



     
 
   

Câu 03: 
1
O
2


  
1
M =3,25cm, O
1
N =33cm , O
2
M = 9,25cm, O
2
N= 67cm, hai n 


 
 
 D
Câu 04: 

                  

A. v = 36cm/s. B. v =24cm/s. C. v = 20,6cm/s. D. v = 28,8cm/s.

Câu 05:  

 
 
 

Câu 06: 
1
, S

2

50Hz
1
S
2


1
, S
2
: Có

A. 9 - 9 . B. 11 - 10 . C. 10 - 11 . D. 9 - 10 .

www.VNMATH.com
Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 23
Câu 07: 

        

A. 21 - - 18 - to. B. 19 - to - 20 - C. 19 - - 20 - to. D. 21 - to - 20 -


Câu 08: 



  


Câu 09:   



  

Câu 10: 
 

  


5. u đim:
Th nhế: 
 
12
2
M
dd



    
và

 
12
()
2

M
dd



    



Th hẬi: 

                570ES thì

Th ậẬ:     




6. Nhc đim và khc phc:
-     


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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 24

PHN MỌ T TH HIN MC  TRIN KHAI
CA  TÀI

+ Trong nm hc 2008 ậ 2009:




BNG TệNH IM BÌNH QUỂN MỌN Lụ
(Theo s liỀ thng kê ẮẬ nhà trng lỀ  ền phòng)


-2009
-2009
12L
9,55
8,90
12T
9,61
8,83
12Si
9,30
x

+ Trong nm hc 2009 ậ 2010:



BNG TệNH IM CÁC BÀI KIM TRA
(Theo s liỀ kho sát ẮẬ ơ tài)


(%)
Kém
(0 =>2.0)


(2.5=>5.0)
Trung bình
(5.5=>6.0)
Khá
(6.6=>7.5)

(8.0=>10)
12L

23

0
0%
0
0%
3
13,04%
2
8,70%
18
78,26%
12T

25

0
0%
0
0%

5
20,00%
3
12,00%
17
68,00%
12Si

30

0
0%
1
3,33%
7
23,33%
6
20,00%
16
53,34%
12A1

40

1
2,50%
2
5,00%
10
25,00%

9
22,50%
18
45,00%
Bng tng hp:




(%)
Kém
(0
=>2.0)

(2.5=>5.0)
Tr. bình
(5.5=>6.0)
Khá
(6.6=>7.5)

(8.0=>10)


130

4
3,08%
10
7,69%
32

24,62%
21
16,15%
63
48,46%


118

1
0,85%
3
2,54%
25
21,19%
20
16,95%
69
58,47%
+ Nhn xét:




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Phng pháp, th thỀt gii nhẬnh ẮáẮ ắng trẮ nghim ềt lý 12
  Trang 25

C. KT LUN
1. Khái quát các kt lun cc b:

  







 

2. Li ích và kh nng vn dng:










- 


 



               


  

     

3.  xut - kin ngh:

               

                 


QỀy Nhn ngày 10 ếhống 5 nm 2010






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