Thiết kế bài giảng vật lý 12 nâng cao (tập 1) phần 2

CHI/ONG III. SONG CO
BAI14

SONG CO - PHl/ONG TRINH SONG
I - MUC TifiU
1. Ve kiln thiic
- Hiiu dupe hien tupng sdng co, nim dupc dinh nghTa song co.
- Quan sat GV tien hanh thf nghiem vl sdng dpc sdng ngang, tir dd, phan biet
dupc sdng dpc va sdng ngang.
- Giai thich dupc nguyen nhan tao thanh sdng co.
- Neu dupc y nghTa cac dai lupng dac trung cho sdng co : bien dp, chu ki, tin sd,
budc sdng, tdc dp truyin sdng.
- Xic dinh dupe bien dp sdng va budc sdng cua sdng trong kenh sdng nude.
- Lap dupc phuang trinh sdng va dua vao phuang trinh nay, neu dupc tinh tuan
hoan theo khdng gian va theo thdi gian ciia sdng.
2. Ve ki nSng
- Quan sit GV tiln hanh thi nghiem, tir dd, riit ra kei luan vl chuyin ddng cua mdi
phin tir cua mdi trudng va chuyin ddng lan truyin cua sdng.
- Giai thich hien tupng vat 11.
- Giai toan vat If vl phuang trinh sdng co, tdc dp truyin sdng va budc sdng.

II-CHUXNBI
Giao viin
- Ld xo dl lam sdng ngang va sdng dpc.
- Kenh sdng nude (neu ed).
- Ve hinh 14.3 va 14.4 SGK tren giiy khd AQ.
- Chuin bi phin mIm Sdng co hpc cua tic gia Pham Xuan Que va may chieu
projector (ne'u cd).
- Phie'u hpc tap cho HS.
123

Hoc sinh
- On lai cac kien thiic vl phuang trinh dao ddng dilu hoa cua con lie Id xo, eac
dai lupng dac trung cua dao ddng.
Ill - THifi'T Kfi' H O A T D 6 N G DAY - H O C
Hoat d d n g cua hgc sinh

Trg giiip cua giao vien

Hoat dgng 1
Kiem tra, chuan bj dieu kien
xuat phat. Dat van de.
HS suy nghT ca nhan tim cau tra
Idi.

HS y thiic dupe van dl ciia bai hpc.

GV neu cau hdi kilm tra kie'n thiie cu:
- Viei phuang trinh dao ddng ciia con
lie Id xo va neu y nghTa cac dai lupng
dac trung ciia dao ddng dilu hoa?
Dgt vdn de : Hing ngay, ta thudng
nghe ndi den sdng nude, sdng am, lan
sdng dien do dai phat thanh truyin di.
Vay sdng la gi ? Nd cd nhiing tfnh chit
gi ? Bai hpc ngay hdm nay giiip chiing
ta nghien ciiu dilu dd.

Hoat dgng 2
Tim hieu hien tugng sdng co hgc.

HS quan sat va md ta hien tupng
- Khi nem vien d i xudng nude,
tren mat nude xuat hien nhirng
vdng trdn ddng tam loi, Idm xen ke
lan rdng din tao thanh sdng nude.

124

GV cho HS xem hinh anh mat nude khi
cd mdt vien da dupc nem xudng qua
may chieu projector va yeu ciu HS mo
ta hien tupng.
GV cho HS xem hinh anh sdng nude
trong kenh tao sdng nude.


Hoat ddng cua hgc sinh

Trg giiip cua giao vien

HS dua ra cae nhan xet khac nhau:

GV neu cau hdi dl HS tim hiiu hien
tupng sdng ca:

Nhdn xet 1 ; - Cac phin tir cua mdi |
trudng dupc truyin di khi sdng lan ;
truyin.
Nhdn xet 2 : - Cac phin tii eiia mdi •
trudng dao ddng tai chd khi sdng ;

lan truyin.
;
Ke't lugn : Mieng xd'p nhd ndi tren ;
mat nude dao ddng len xudng tai :
chd, cdn cac dinh sdng chuyin ;
ddng theo phuang nim ngang ngay i
cang ra xa tam dao ddng. Vay cac ;
phin tir ciia mdi trudng dao ddng
tai chd khi cd chuyin ddng Ian
truyin sdng trong mdi trudng.

- Nhan xet gi vl chuyin ddng cua mdi
phin tu cua mdi trudng truyin sdng khi
ed chuyin ddng Ian truyin sdng trong
mdi trudng ?
GV tie'n hanh thi nghiem vdi kenh sdng
nude khi bd mdt mieng xd'p nhd ndi tren
mat nude dao ddng va yeu ciu HS riit ra
kei luan.

GV thdng bao:
HS tie'p thu, ghi nhd khai niem.

- Sdng ea la dao ddng ca lan truyin
trong mdi trudng.
GV tie'n hanh thi nghiem vdi Id xo trong
hai trudng hop a) va b), yeu ciu HS
nhan xet vl phuang dao ddng ciia cac
phin tir cua mdi trudng vdi phuong
truyin sdng.

1^

Trudng hpp a)

>

- Cae phin tir dao ddng vudng gdc ;
vdi phuang truyin sdng.
Trudng hpp b)

•

- Cic phin tii dao ddng theo |
phuang truyin sdng.
|

. ^[]

>
A

GV thdng bao:
- Khi eac phan tii cua mdi trudng dao

125


Hoat ddng ciia hgc sinh
HS tie'p thu, ghi nhd khai niem.

Trg giiip cua giao v i i n
ddng theo phuang vudng gdc vdi
phuang truyin sdng, ta ed sdng ngang.
^ Khi eac phan tir cua mdi trudng dao
ddng theo phuang truyin sdng, ta ed
sdng dpc.

Hoat dgng 3
Giai thich sir tao thanh sdng co
HS quan sat, suy nghT ea nhan, sau
dd thaof luan chung toan Idp.

GV cho HS quan sat hinh ve bilu diln
md hinh ciia eic phin tii sdng
ngang(hinh 14.3 SGK) d nhiing thdi
dilm lien tiep va neu cau hdi dl HS giai
thfch sur tao thanh sdng co.

- GiQa eac phin tii cua spi day dan
hdi cd luc dan hdi lien kei chiing.

- Giiia cic phin tit cua spi day dan hdi
cd luc lien kei khdng ? Luc dd la luc gi ?

- O thdi dilm ban diu t = 0, tat ca
eic phin tir cua day diu diing ydn
d vi tri 7.

- Hien tupng gi xay ra neu giiia chiing

khdng cd luc lien ket ?

T
- Trong khoang thdi gian / = —.
phin tir 0 chuyin ddng tu vi trf can
bing len vi trf cao nhat. Trong khi
dd, luc lien kei dan hdi keo phin tir
1 chuyin ddng theo, nhung chuyin
ddng sau mdt chiit. Cung nhu the,
chuyin ddng dupc truyin de'n phin
tir 2, sau phin tir 1 mdt chiit. Day
cd vi tri II.
- Phin tir 0 tie'p tuc thuc hien dao
ddng va dao ddng nay lin lupt
dupe truyin cho cac phan tir tie'p
theo cua day. Cae phin tir nay thuc
hien dao ddng cimg tin so, cung
bien dp vdi phin tir 0 nhung tri
pha hon.

126

- Truyin cho phin tir 0 mdt dao ddng
theo phuang thing diing cd chu ki dao
ddng T. Nhan xet su chuyin ddng eiia
cac phin tur ke tiep d cac thdi dilm tie'p
theo.
- Hay chi ra vi tri va hudng chuyin
ddng cua cic phin tir so 6 va sd 12 ciia
, T 3T

5T
Id xo d cac thdi diem —; — \T; —;...?
2
2 2
(GV dimg cac mui tdn dl chi hudng
chuyin ddng cua cac phin tir khi HS tra
Idi).
- Nhan xet gi vl pha dao ddng cua cac
phin tir cang d xa tam dao ddng ?


Hoat d d n g cua hgc sinh

Trg giiip cua giao vien

- Cac phin tir cang xa tam dao
ddng thi cang tri pha hon cac phin
tir gin tam dao ddng.
GV thdng bao:

HS tie'p thu, ghi nhd.

- Sdng CO dupc tao thanh nhd lire lien
kei dan hdi giua eac phan tur ciia mdi
trudng truyin dao ddng. Mdi trudng nao
cd luc dan hdi xuit hien khi hi bien
dang lech thi truyin sdng ngang. Neu
luc dan hdi xuat hien khi cd bien dang
nen, dan thi mdi trudng truyin sdng
dpc.

Hoat dgng 4
Tim hieu nhOmg dai lugng ddc
trung ciia chuyen ddng sdng
HS dpc SGK, sau dd thao luan
chung toan Idp.
- Tit ca cac phin
trudng diu dao ddng
kl va tin sd bing chu
nguon dao ddng gpi
tin sd ciia sdng.

tir ciia mdi
vdi cimg chu
ki, tin sd ciia
la chu ki va

- Bien dp sdng tai mdi dilm trong
khdng gian chfnh la bidn dp dao
ddng cua phin tir mdi trudng tai
dilm dd. Trong thue te, cang ra xa
tam dao ddng thi bien dp sdng
cang nhd.
- Budc sdng la quang dudng sdng
truyin di dupc trong mdt chu ki
dao ddng. Hai dilm each nhau mdt
budc sdng dao ddng cung pha vdi
nhau.

GV yeu ciu HS dpc SGK muc 2, sau dd
neu cac cau hdi dl HS tim hiiu cac dai

lupng dac tnmg cua chuyin ddng sdng:

- So sinh chu ki va tan so ciia cic phin
tir cua mdi trudng vdi chu ki va tin so
cua ngudn dao ddng.
- Bien dp sdng dupc xac dinh nhu the'
nao? Nhan xet gi vl bien dp sdng tai
nhirng dilm d xa tam dao ddng ?
- Budc sdng la gi ? Hai dilm each nhau
mdt budc sdng cd dac dilm gi ?
- Tdc dp truyin sdng dupc xac dinh
bing cdng thiic nao ?
- Ban chit ciia qua trinh truyin sdng la

127


Hoat ddng cua hgc sinh

Trg giiip cua giao vidn

- Tdc dp truyin sdng dupc xic
dinh :
v=

T

^=fX

- Sdng truyin dao ddng cho cac

phan tir ciia mdi trudng, nghTa la
truyin cho chiing nang lupng. Qua
trinh truyin sdng la qua trinh
truyin nang lupng.
- Mdt HS dung thudc va biit da len
xac dinh budc sdng va bien dp
sdng ciia sdng trong kenh sdng
nude.

GV yeu ciu HS xac dinh budc sdng va
bien dp sdng ciia sdng trong kenh sdng
nude.

Hoat dgng 5
Lap phuang trinh sdng, tir dd
suy ra mdt sd' tinh chat ciia sdng

GV neu cau hdi dl HS lap phuang trinh
sdng:

HS suy nghT ci nhan, sau dd thao
luan chung toan Idp.

- Gia sir dao ddng cua phan tii 0 cua
sdng la dilu hoa, Ii dp u bie'n thien theo
thdi gian : u = A cos cot thi diem M each
0 mdt khoang x cd phuang trinh dao
ddng nhu the' nao ?
GV neu cac cau hdi gpi y:

Ta cd phuang trinh dao ddng ciia
dilm 0 la:
u = Acoscot =

2;r
Acos—t
T
X

Sau khoang thdi gian t = — sdng
V

dupc truyin tdi diem M nen
phuong trinh dao ddng cua M cd
dang :

128

- Xet sdng truyin dpc theo true Ox, bd
qua luc can dl bien dp dao ddng tai mpi
dilm la nhu nhau. Dao ddng cua dilm
M sdm pha hon hay tri pha han dao
ddng ciia dilm 0 ?
- Sau khoang thdi gian bing bao nhieu
thi dao ddng dupc truyin de'n diem M ?


Hoat ddng cua hgc sinh
/

Trg giiip cua giao vien

.\

Mw(0 = ^COS —
f

(1)

•Uj^it) = ACOS2TT - - - I
T X

GV thdng bao:
HS tie'p thu, ghi nhd.

- Phuang trinh (1) la phuang trinh dao
ddng ciia dilm M ed toa dp x tren
phuang truyin sdng tai thdi dilm t gpi
la phuang trinh sdng.

Xet dilm tren dudng truyin sdng
cd toa do X = d. Thay x = d vao
phuang trinh (1) ta dupc:

GV neu cau hdi dl HS tim hiiu mdt sd
tinh chai cua sdng:

2;r 2TTd
Up = A cos - / - ^T
A ,

Chuyin ddng cua P la mdt dao
ddng tuin hoan theo thdi gian
vdi chu ki T
Xet vi tri cic dilm cua sdng tai
mot thdi dilm xac dinh IQ. Ta ed:
M(X,/O) = ^COS

2TT_

T '

'

2TT
X

- Tir phuang trinh sdng, suy ra tinh tuin
hoan ciia sdng theo thdi gian va khdng
gian.
- Xet dilm P tren dudng truyen sdng cd
toa do X = d, sau khoang thdi gian bing
bao nhieu thi dilm P thuc hien dupc
them mdt dao ddng toan phin ?
- Xet tai mdt thdi dilm IQ bat ki, sau
quang dudng bing bao nhieu thi hinh
dang sdng dupc lap lai nhu cu ?

A
Tir phuong trinh ta thay li dp u
bie'n thien tuin hoan theo toa dp

X, nghTa la cii sau mdi khoang cd
dp dai bing mdt budc sdng, sdng
lai cd hinh dang lap lai nhu cQ.
Hoat dgng 6
Lam bai tap ap dung
HS suy nghT ca nhan, sau dd thao
luan chung toan Idp.

GV yeu ciu HS lam bai tap I trong
phie'u hpc tap.

129


Hoat d d n g cua hgc sinh
a) 1 a CO V = — =
= 4m / .v
t
0.3
Budc sdng : A = v.r = 4.1,6 = 6,4m
b) Phuang trinh sdng ciia P ed
dang:
Upit) = ACOS2TT

'^

( t

x\

[T

=> Upit) = 0,02cos

Trg giiip cua giao vidn
GV neu cac cau hdi gpi y:
- Tdc dp truyin sdng dupc xic djnh
bing cdng thiic nao ?
- Budc sdng va tdc dp truyin sdng lien
he vdi nhau nhu the nao ?
- Phuang trinh truyin sdng tai dilm P
cd dang nhu the' nao ?

A
^ TTt

0,8

TT^

2

im)

c) Tai thdi dilm t = 3,2s, dilm P
cd li dp la :
^7r.3,2 ; r )
Upit) = 0,02 COS
0,8 ~2
= 0 , 0 2 c o s - = 0(m)

2
Hoat ddng 7
Cung cd bai hgc va dinh hudng
nhiem vu hgc tap tie'p theo
HS lam viec ea nhan, sau dd thao
luan chung toan Idp.

GV yeu cau HS tie'p tuc lam viec vdi
phie'u hpc tap dl ren luyen each lam bai
tap trie nghiem khach quan phan sdng
CO hpc.

- HS vl nha lam eac bai tap 1, 2, 3, 4
SGK.
- On tap cac kien thiic vl phuang
trinh sdng.

PHIEU HOC TAP
Cau 1. Cho mdt spi day cao su nim ngang. Lam cho dau C ciia day dao ddng theo
phuang thing diing vdi bien dp 2cm va chu ki l,6i-. Tai thdi dilm r = 0, C
cd li dp cue dai. Sau 0,3i- thi dao ddng dupc truyin di dupc 1,2m dpc theo day.
a) Tim budc sdng.

130


b) Viei phuang trinh dao ddng ciia mdt dilm P a each diu day mdt doan la
1,6m. Chpn md'c thdi gian la liic bit dau truyin dao ddng cho C tir vi tri
cd li dp cue dai.
c) Xac dinh li dp 7' d thdi dilm / = 3,2s.

Cau 2. Kit luan nao sau day diing khi ndi vl chu ki va tin sd cua cac phin tir dao
ddng ciia mdi trudng truyin sdng ?
A. Cac phin tii d gin tam dao ddng cd chu ki va tin sd Idn nhat.
B. Tat ca cae phin tir dao ddng vdi cung chu k i . cimg tan sd.
C. Cang xa tam dao ddng, cac phan tir cd chu ki va tin sd cang Idn.
D. Tai ea eac phin tir dao ddng vdi chu ki va tin sd bit ki.
Cau 3. Budc sdng la
A. khoang each giiia hai phin tir dao ddng tren phuang truyin sdng.
B. quang dudng sdng truyin di dupc trong 1 phiit.
C. khoang each giira hai phin tir dao ddng eiing pha gin nhau nhat tren
phuang truyin sdng.
D. quang dudng sdng truyin di dupc trong 1 giay.
Cau 4. Phat bilu nao sau day diing khi ndi vl pha dao ddng ciia cac phin tir dao
ddng trong mdi trudng truyin sdng ?
A. Cac phin tir xa tam dao ddng sdm pha hon cac phin tir gin tam dao ddng.
B. Tit ca cae phin tir dao ddng trong mdi trudng cd ciing pha dao ddng.
C. Cac phin tir gin tam dao ddng sdm pha hon cac phin tir xa tam dao ddng.
D. Cac phin tir nam trong khoang each bing mdt budc sdng cd cung pha
dao ddng.
Cau 5. Phat bilu nao sau day sai khi ndi vl tdc dp truyin sdng ?
A. Td'e dp truyin sdng chinh la tdc dp truyin cac phin tir dao ddng.
B. Td'e dp truyin sdng chinh la tdc dp truyin pha dao ddng.
C. Tdc dp truyin sdng bing thuang sd giira budc sdng va chu ki dao ddng.
D. Td'e dp truyin sdng bing tich sd giira tin so sdng vdi budc sdng.
Cau 6. Mdt sdng co hpc cd chu ki bing 0,00Is truyin di vdi tdc dp 340mls thi
budc sdng ciia nd la
A. 340m.

B. 34m.

C. 3,4m.

D. 0,34m.
131


Cau 7. Ban Anh lam mdt thi nghiem vdi kenh sdng nude, khi nhin thay mat cit
ciia nude trong kenh sdng nude cd dang hinh sin thi ban ay bd mdt mieng
xd'p ndi tren mat nude. Sau mdt chu ki dao ddng cua sdng nude trong kenh
sdng thi mieng xd'p se
A. dich chuyin dupc mdt budc sdng.
B. dich chuyin vl phia cud'i cua kenh sdng nude.
C. dich chuyin len phfa diu ciia kenh sdng nude.
D. dao ddng len xudng tai vi trf tha.

BAI15

PHAN XA SONG - SONG D U N G
I - MUC TifiU
1. Ve kien thiic
- Md ta dupc hien tupng thu dupc khi quan sat giao vien lam thf nghiem vl sir
phan xa sdng va hien tupng sdng dimg tren Id xo va tren spi day.
- Giai thich dupc su tao thanh sdng dtmg.
- Hiiu dupc hien tupng sdng dirng, phan biet dupc nhirng dilm niit va nhii'ng
dilm bung.
- Van dung cac kien thiic vl sdng dimg dl lam mdt so bai tap don gian nhu xac
dinh budc sdng tren spi day cd sdng dimg, xac dinh tdc dp truyin sdng...
2. Ve ki nang
- Quan sit GV tien hanh thf nghiem, tir dd, riit ra kdt luan vl su phan xa sdng.
- Giai thich hien tupng vat li.

- Giai toan vat li vl hien tupng sdng dimg.
II - C H U X N BI

Giao viin
- Ld xo dl lam sdng ngang va sdng dpc.
- Kenh sdng nude (ne'u cd).
- Bd thi nghiem vl sdng diing tren mdt spi day dan hdi.
- Phie'u hpc tap cho HS.
132


Hpc sinh
- On tap cae kie'n thiic vl phuang trinh sdng.
Ill - THifi'T Kfi' HOAT D 6 N G DAY - HOC
Hoat ddng cua hgc sinh
Hoat dgng 1
Kiem tra, chuan bj dieu kien
xuat phat.
HS suy nghT ca nhan tim cau tra
Idi.

Trg giiip cua giao vien
GV neu eau hdi kilm tra kie'n thiie cu:
- Mdt ngudn sdng dao ddng vdi phuong
trinh u = Acosat. Viei phuang trinh
dao ddng cua dilm M tren phuong
truyin sdng each ngudn sdng mdt doan
bing d ?

Hoat dgng 2

Tim hieu su phan xa sdng va
hien tugng sdng dimg
HS chii y quan sat va md ta hien
tupng.
- Kit qua thi nghiem cho thay :
sau khi dap vao thanh cua kenh
sdng, bie'n dang se truyin ngupe
trd lai.

- Bie'n dang dupc truyin din diu
cd dinh ciia Id xo thi bi truyin
ngupc trd lai.
- Khi bie'n dang dupe truyin
ngupc trd lai d thanh kenh sdng
nude hoac d diu ed dinh ciia Id xo
thi ngupc chilu vdi chilu ciia bien
dang truyin tdi.

GV tie'n hanh thf nghiem vdi Id xo va
vdi kenh sdng nude vl hien tupng sdng
phan xa, ydu ciu HS quan sat va md ta
hien tupng.
- Bd tam khir phan xa ra khdi kenh
sdng. Cho ddng co hoat ddng trong thdi
gian rat ngin (hai vat tao sdng thue hien
dupe 1-2 chu ki chuyin ddng len
xudng). Khi dd, xuit hien mdt bien
dang lan truyin tren mat nude. Hien
tupng gi xay ra khi bien dang truyin tdi
thanh eiia kenh sdng nude ?

- Cim mdt diu A ciia Id xo dua len dua
xudng gay ra mdt bie'n dang tren Id xo.
Hien tupng gi xay ra khi bien dang nay
truyin dpc theo Id xo din diu ed dinh
cua Id xo ?
- Hay so sanh chilu bie'n dang khi
tmyin ngupc trd lai vdi chilu ciia bien
dang khi dupc truyin tdi thanh ciia
kenh sdng nude hoac den diu cd dinh
ciia Id xo ?

133


Hoat ddng ciia hgc sinh

HS tie'p thu, ghi nhd.

Trg giiip ciia giao vien
GV thdng bao vl su phan xa sdng:
- Neu cho dau ciia Id xo thue hien mot
dao ddng dilu hoa theo phuong vudng
gdc vdi Id xo thi xuat hien mdt sdng
truyin de'n B gpi la sdng tdi. Sau dd, dao
ddng dupc truyin ngupc lai tao thanh
sdng phan xa.
- Thuc nghiem chiing td, sdng phan xa
cd ciing tin so va ciing budc sdng vdi
sdng tdi. Nlu diu phan xa cd dinh thi
sdng phan xa ngupe pha vdi sdng tdi.

HS ehii y quan sat GV tien hanh
thi nghiem va md ta hien tupng.

GV tie'n hanh thi nghiem tang tin sd
dao ddng dilu hoa ciia mdt diu Id xo
hoac mdt diu spi day dl HS quan sat
va yeu ciu HS md ta hien tupng quan
sat duoc

- Khi tang din tin so dao ddng cua
Id xo, de'n mdt liic ta khdng cdn
phan biet dupc sdng tdi va sdng
phan xa niia. Liic dd tren Id xo
xuat hien nhimg dilm diing yen
xen ke vdi nhirng diem dao ddng
vdi bien dp kha Idn.
- Khi tang din tin sd dao ddng cua
spi day bing viec thay ddi tdc dp
ciia ddng co gin tren la thep dan
hdi. Hien tupng thu dupc gic j
nhu hien tupng d tren.

"ZrS^^ifei^sSrt^WiJ^ s?

GV thdng bao vl hien tupng sdng dimg:
- Hien tupng thu dupc d thf nghiem tren
la hien tupng sdng dimg. Nhiing dilm
diing yen tren Id xo hoac tren spi day la

134


Trg giiip cua giao vien

Hoat ddng cua hgc sinh

nhiing diem niit, nhihig dilm dao ddng
vdi bien dp cue dai gpi la nhimg dilm
bung. Nhirng niit va bung xen ke, each
diu nhau.
Hoat dgng 3

«
GV neu cau hdi dl HS giai thich hien

Giai thich su tao thanh sdng •
dimg tren sgi day

tupng:
- Hay giai thich hien tupng thu dupc d
tren ?

HS thao luan chung toan Idp.
Xet dilm M tren spi day, dao ddng ;
ciia dilm M la tdng hpp 2 dao
ddng do sdng tdi truyin tdi M va \
sdng phan xa tir B truyin tdi M.
•

GV neu cac cau hdi gpi y:
- Xet mdt dilm M tren spi day cd mdt
diu CO dinh, khi mdt dau spi day dao
ddng dilu hoa thi dilm M thuc hien
nhirng dao ddng tit dau truyin tdi ?

Phuong trinh dao ddng cua dilm B \
cd dang :
Ug = A cos 2;r/r

Song tdi
VV\^

d
>.

A

M

;

\
^

- Gia sir tai thdi dilm t, sdng tdi truyin
de'n B va phuang trinh dao ddng cua
sdng tdi tai fi la Ug= A cos 27Tft thi
phuong trinh dao ddng do sdng tdi
truyin din M each B mdt doan d cd

dang nhu the' nao ?

IB|

< ^
Song phan xa

- Dilm M dao ddng sdm pha hay tre
pha hon dilm B ?
Suy ra phuong trinh dao ddng ciia \
dilm M:
i
(^ ^ 2TTd]
U;^ = A cos 2TTft +
A

i

- Dac dilm cua sdng phan xa tai dilm B
la gi ?
- Dilm B CO dinh nen pha dao ddng ciia
sdng phan xa tai B cd dac dilm nhu the'
nao ?

135


Hoat ddng cua hgc sinh

Trg giup cua giao viin

Sdng phan xa d fi cd li dp ngupc
chilu vdi li dp eiia sdng tdi. Do dd
phuang trinh cua sdng phan xa d fi
la:
Ug =-AC0s2TTf, =

Ac0s[2TTft-TT)

Sdng phan xa tir B truyin de'n M,
phuang trinh sdng phan xa tai M la :
*M

Acos

2TTft - TT •

2TTd

Ta cd phuang trinh dao ddng tdng
hpp ciia dilm M :

- Sdng phan xa truyin den M cd phuong
trinh nhu the nao ?
- Sdng phan xa truyin den M sdm pha
hay tri pha hon sdng phan xa tai B ?
- Hay xac dinh phuang trinh dao ddng
tdng hop cua dilm M ?

U=UM+UM

2TTd

u = 2 Acos

TT

A

2)

xeos 2TTft

TT

Bien dp dao ddng tdng hop ciia
dilm M la:
2TTd

a = 2 Acos

TT

—

A

2)

Nlu M dao ddng vdi bien dp cue

dai thi:
2TTd

TT '

y A
(2TTd

2
TT\
-f—

\ A

= kTT

2)

(

d = k+'2

136

±1

+

cos

A

- Hay xac dinh vi trf cua nhihig diem
dao ddng vdi bidn dp cue dai, nhihig
dilm khdng dao ddng tren spi day khi
xuat hien sdng dimg ?


Hoat dgng cua hgc sinh
Nlu M khdng dao ddng thi:
2TTd

cos

TT ,

+A
2

'2TTd

Trg giiip cua giao vien

„

=0

7T\

= (2A: + 1)TT

+
^
A 2

'd = k

A

vay, neu khoang each d bing so
nguyen lin nira budc sdng thi bien
dp dao ddng tai dd bing 0, dilm M
la mdt niit sdng.
Nlu khoang each d = k +

1 U

thi bien dp dao ddng tai dd cd gia
tn ciic dai, diem M la mdt dilm
bung sdng.
HS thao luan chung toan lap.

GV neu eau hdi dl HS tim dilu kien dl
cd sdng diing tren spi day:
- Tim dilu kien dl cd sdng dimg trdn
spi day cd hai diu cd dinh va spi day cd
mdt diu cd dinh va mdt diu tu do?

- Ddi vdi spi day ed hai diu cd
dinh hay mdt diu spi day cd dinh
va mdt diu dao ddng vdi bidn dp

nhd, khi cd hien tupng sdng dimg
tren spi day, chilu dai spi day
dupe xac dinh:

GV neu cau hdi gpi y:

A
l = n— vdi rt = 1, 2, ... n la sd
2
bung sdng quan sat dugc tren spi
day.

- Dd'i vdi spi day cd hai diu cd dinh thi
hai dau cd dinh dd ddng vai trd la niit
sdng hay la bung sdng ?
- Khoang each giiia hai mit lien tiep
hoac hai bung lien tiep bang bao nhieu ?
- Gia sir tren spi day cd hai diu cd dinh
de'm dupc n bung sdng thi chilu dai spi
day bing bao nhieu ? Chilu dai spi day

137


Hoat d d n g cua hgc sinh
- Ddi vdi spi day cd mdt dau tu do
thi dau tu do phai la mdt bung
sdng. Chilu dai spi day bing mdt
so le lin mdt phin tu budc sdng:
I = m— vdi m = 1, 3. 5, ...

4

Trg giiip cua giao vien
lien he nhu the' nao vdi budc sdng va sd
bung sdng ?
- Ddi vdi spi day cd mdt dau cd dinh va
mdt diu tu do thi diu day nao ddng vai
trd la nut sdng, diu day nao ddng vai tro
la mdt bung sdng ?
- Khoang each giira mdt niit sdng va
mdt bung sdng kl nhau bing bao nhieu ?

Hoat dgng 4
Lam bai tap ap dung
HS lam viec ca nhan, sau dd thao
luan chung toan Idp.
Spi day ed hai dau cd dinh. Dilu
kien dl cd sdng dimg tren spi day
la:
2
=^ /I = — = 30cm
n

GV yeu ciu HS lam bai tap 1 trong
phie'u hpc tap.
GV neu eac cau hdi gpi y.
- Hai dau spi day la hai mit sdng hay
hai bung sdng ?
- Dilu kien dl cd sdng dimg tren spi
day la gi ?

- Td'e dp truyin sdng tren spi day dupc
xic dinh bing cdng thiic nao ?

Tdc dp tmyIn sdng tren spi day la :
v = / A = 50.30 = 1500cm/5.
Hoat dgng 5
nhiem vu hgc tap tie'p theo

GV yeu ciu HS lam cac bai tap trie
nghiem khach quan trong phieu hpc tap.

HS lam viec ca nhan, sau dd thao
luan chung toan Idp.

- HS vl nha lam cac bai tap 1, 2, 3, 4
SGK.

Cling cd bai hgc va dinh hudng

- On lai cac kiln thiic vl phuang trinh
sdng, sdng dimg.

138


PHIEU HOC TAP
Cau 1. Trong mdt thi nghiem, ngudi ta diing may rung vdi tin sd / = 5077z dl
truyin dao ddng cho mdt diu spi day dan hdi cd chilu dai 60cm, dau kia
eiia day dupc giir cd dinh. Ngudi ta quan sat thay sdng dimg tren day va
dem dupc 4 bung sdng. Xac dinh budc tren day va td'e dp truyin sdng.

Cau 2. Khi cd sdng dimg tren spi day thi budc sdng dupc xac dinh bing
A. chilu dai spi day.
B. khoang each giira hai niit sdng hoac hai bung sdng.
C. khoang each giiia hai nut sdng hoac hai bung sdng ke' tiep.
D. hai lan khoing each giiia hai niit sdng hoac hai bung sdng ke' tilp.
Cau 3. Quan sat sdng dimg tren mdt spi day, mdt ban riit ra kei luan : khoang each
giua hai bung sdng ke' tie'p bang
A. mdt budc sdng.
B. hai budc sdng.
C. nira budc sdng.
D. mdt phin tu budc sdng.
Cau 4. Sdng dimg dupc tao ra tren day AB = 11cm vdi dau B tu do, dau A cd dinh.
Budc sdng bing 4cm. Tren day cd:
A. 6 bung sdng va 6 mit sdng.
B. 5 bung sdng va 6 niit sdng.
C. 6 nut sdng va 5 bung sdng.
D. 5 bung sdng va 5 mit sdng.
Cau 5. Mdt spi day chilu dai /, hai diu A, B cd dinh. Khi cho spi day dao ddng thi
tren day xuit hien sdng diing. Kep mdt mau giiy nhe tren spi day, di
chuyin miu giiy dd dpc theo chilu dai spi day thi tha'y ed 2 vi tri tren spi
day mau giay khdng hi rai. Budc sdng dupc xac dinh:
A. A = l.
3
C. A = -l.
2

B. A = -2
2
D. A = -l.
3

139


BAI16

GIAO THOA SONG
I - MUC TifiU
1. Ve kien thiifc
- Dua ra dupc du doan vl su tao thanh van giao thoa tren mat nude.
- Ap dung phuang trinh sdng va kei qua cua viec tim sdng tdng hop cua hai song
ngang eiing tan sd va cimg pha dl kilm tra du doan bing con dudng If thuyei.
- Nim dupc dilu kien dl cd hien tupng giao thoa.
- Nim va md ta dupc hien tupng nhilu xa cua sdng nude qua mdt khe hep.
- Van dung eac kiln thiic vl giao thoa de lam mdt sd bai tap trie nghiem khach
quan vl hien tupng giao thoa.
2. Ve kl n a n g
- Quan sat GV tiln hanh thi nghiem, tir dd, riit ra ket luan vl su phan xa sdng.
- Giai thfch hien tupng vat li.
- Ren luyen cho HS dua ra du doin ed can cii.
- Ren luyen cho HS giai cac bai tap trie nghiem khich quan vl hien tupng giao thoa.

II-CHUXNBI
Giao

viin

- Chuan bi phin mIm Sdng co hpc ciia tic gia Pham Xuan Que' va miy chieu
projector (neu cd) dl md phdng hien tupng giao thoa sdng ca hpc.
- Chuan hi bd thi nghiem vl khay sdng nude dl lam thf nghiem vl giao thoa sdng

nude va hien tupng nhilu xa sdng nude qua mdt khe hep.
- Phie'u hpc tap cho HS.
Hpc sinh
- On lai cic kiln thiic vl phuang trinh sdng, sdng dimg.

140


Ill - THifi'T Kfi' HOAT D 6 N G DAY - HOC
Hoat ddng cua hgc sinh

Trg giiip cua giao v i i n

Hoat dgng 1
Kiem tra, chuan bi dieu kien
xuat phat. Dat van de
HS suy nghT ca nhan tim eau tra
Idi.

HS nhan thiie dupc vin dl cua bai
hpc.

GV neu cau hdi kiem tra kie'n thirc cu:
- Hay van dung phuong trinh sdng dl
giai thich hien tupng sdng dung tren spi
day dan hdi.
Dgt vdn de : Bai hpc trudc chiing ta da
nghien ciiu hien tupng sdng dimg tren
mdt spi day dan hdi ma dao ddng ciia
mdi dilm tren spi day la tdng hpp ciia

hai dao ddng do sdng tdi va sdng phan
xa tren spi day truyin tdi. Hdm nay,
chiing ta nghien ciiu dao ddng cua mdt
dilm ciia mdi trudng truyin sdng ma
trong mdi trudng truyin sdng cd hai
ngudn sdng.

Hoat dgng 2
Nghien ciiru su giao thoa cua hai
song tren m$t nude
HS thao luan nhdm, sau dd dai
dien nhdm dua ra cac du doan.
- Tuong tu nhu hien tupng sdng
dimg, ta se thiy tren mat nude xuit
hien nhiing dilm khdng dao ddng
va nhirng dilm dao ddng vdi bien
dp cue dai.

Giao vien neu cau hdi vl vin d l cin
nghien ciiu:
- Hien tupng gi xay ra khi cho hai
ngudn dao ddng S,, S2 ciing tin sd, ciing
pha dao ddng tren mat nude ciia mdt
khay nude ?
GV neu cau hdi gpi y:
- Xet mdt dilm M tren mat nude, dao
ddng ciia dilm M duac truyin tir dau tdi ?
GV neu cau hdi dl HS kilm tra du doan
bing con dudng 11 thuyei
- Bing if thuyei cd thi kilm tra du doan

tren nhu the' nao?

S,

S2

141


Hoat d d n g ciia hgc sinh

Trg giiip cua giao vien

Hai ngudn 5,, 52 dao ddng eiing
tin sd, ciing pha thi hai sdng chiing
tao thanh cd ciing budc sdng.
Phuang trinh dao ddng ciia hai
ngudn 5|, 52 cd dang :

GV neu cau hdi gpi y dl HS kilm tra du
doan bang eon dudng li thuyet.

i] = U2

2;r

A

Acos—t
T

- Tai dilm M cd hai dao ddng do
hai ngudn sdng truyin de'n la :
f
\M = ACOS2TT

d^_\
T

"2W "= ^eos2;r

A]

AJ

Dp lech pha ciia hai dao ddng do
hai ngudn sdng truyin de'n la :
^(P =

^[d2-d\)

Dao ddng tai M la tdng hpp hai
dao ddng tir 5, va 52 truyin den :
Bien dp dao ddng tai M phu thudc
vao dp lech pha giira hai dao ddng
va ed gia tri la :
AII = A^ + AI + 2A]A2 cos Acp
=

2A^+2A^cosA(p

^ All =2A^[\ + cosAcp)
A,,=2A

142

Acp
eos-

- Hai ngudn 5,, 52 dao ddng ciing tin
so, eiing pha thi hai sdng chiing tao
thanh ed budc sdng nhu the' nao neu coi
bien dp dao ddng eiia hai ngudn bing
nhau ?
- Phuang trinh dao ddng eiia hai ngudn
5|, 52 cd dang nhu the' nao neu coi bien
dp dao ddng ciia hai ngudn khdng thay
ddi trong qua trinh truyin sdng ?
- Hai dao ddng thanh phin ciia dilm M
do hai ngudn 5|, 52 truyin den cd dang"
nhu the' nao ?
- Xac dinh dp lech pha cua hai dao
ddng thanh phin cua dilm M va bien dp
ciia dao ddng tdng hop tai M ?


Hoat ddng ciia hgc sinh

Trg giiip cua giao vien

Nlu dilm M dao ddng vdi bien dp
cue dai thi :

- Xac dinh nhiing diem dao ddng vdi
bien dp cue dai va nhirng diem khdng
dao ddng.

Acp
cos

~Y

Acp

• kTT => Acp = 2^;r, suy ra

hai dao ddng dupc truyin de'n tir
hai ngudn 5,, 52 ddng pha.
2TT

=> A^ = — [d2-d])
A
^ d2-d]

= 2kTT

=kA

vdi A: = 0,±l,±2,...
Ne'u dilm M khdng dao ddng thi:

Acp
cos-

0

^ ^ = [2k + X)'L
2
^
^2
^ Acp = [2k + \)TT, suy ra hai dao
ddng dupc truyin de'n tir hai ngudn
5|,52 ngupc pha.
2TT

=>Acp = ~[d2-d])
A
^d',-d^

r

= [2k + \)TT

1 1

= k+ - A
2

vdi ^ = 0,±1,±2,...
- Nhiing dilm dao ddng vdi bien
dp cue dai cd hieu dudng di :

d2-d] =kA vdi A: = 0,±1,±2,...

- Xac dinh quy tich ciia nhirng dilm M
dao ddng vdi bien dp cue dai va quy tfch
ciia nhimg dilm M khdng dao ddng.

Thay k = 1, ta ed :

143


Hoat d d n g cua hgc sinh

Trg giiip cua giao vien

d2-d] = A = hing so
Tap hpp nhirng dilm M dao ddng
vdi bien dp cue dai cd hieu sd
khoang each tir M de'n hai dilm cd
dinh bing hing sd la mdt dudng
hypebol.
Tuong tu, tap hpp nhiing dilm M
dao ddng vdi bien dp cue tilu cd
hieu
sd
khoang
each
3
d2-d] = — A = hang sd (vdi k =
1) ciing l i mdt hypebol.

- Lin lupt cho k nhirng gia tri
^ = ±l,±2,...ta dupc mdt hp
dudng hypebol cua nhiing dilm
dao ddng vdi bien dp cue dai xen
ke vdi hp cac dudng hypebol cua
nhiing dilm khdng dao ddng.
HS thao luan nhdm, sau dd dai
dien nhdm len bio cao kei qua.
- Cin phai cd hai ngudn sdng dao
ddng ciing pha, ciing tin so dao
ddng tren mat nude ciia khay nude.
HS chii y quan sat GV tie'n hanh
thi nghiem va riit ra ket luan
- Quan sat mat nude, ta thay tren
dd xuai hien cac dudng hypebol
diing nhu du doan.

GV neu cau hdi dl HS thiet ke' phuang
an thf nghiem kilm tra:
- Hay thiet ke mdt phuang an thf
nghiem kilm tra.
GV gidi thieu thi nghiem va tien hanh
thf nghiem vdi khay sdng nude, yeu ciu
HS quan sat va nit ra kei luan.

GV thdng bao:
- Hai ngudn cd cimg tan sd va cd dp
lech pha khdng ddi theo thdi gian ggi la

144

Hoat ddng cua hgc sinh
HS tie'p thu, ghi nhd.

Trg giiip cua giao vien
hai ngudn kei hpp. Hai sdng do hai
ngudn kei hpp tao ra gpi la hai sdng kei
hop.
- Hien tupng hai sdng kei hpp, khi gap
nhau tai nhirng dilm xac dinh, ludn ludn
hoac tang cudng lin nhau, hoac lam ye'u
nhau dupc gpi la sir giao thoa cua sdng.
- Dilu kien dl cd hien tupng giao thoa
la hai sdng phai xuit phat tir hai ngudn
dao ddng ciing tin so, ciing phuong va
cd dp lech pha khdng ddi theo thdi gian.

Hoat dong 3
Tim hieu su nhilu xa ciia sdng
va irng dung cua hien tugng giao
thoa
HS lam viec ci nhan tim hiiu ling
dung ciia hien tupng giao thoa.
'•
- Ne'u khdng quan sat dupc qua
trinh sdng, nhung ta phat hien ra ;
hien tupng giao thoa thi cd thi kei |
luan qua trinh dd la qua trinh sdng. •
HS quan sit va md ta hien tupng: i

Phfa trudc khe hep, ta quan sat ;
dupc su lan truyin cua sdng trdn •
cd tam phat sdng d vi tri hdn bi ;
cham vao mat nude. Phia sau khe ;
hep, ta quan sat dupc su lan ;
truyin cua sdng trdn khac ma
khe hep chfnh la tam phat sdng.

GV yeu ciu HS dpc SGK va tra Idi cau
hdi dl tim hiiu ling dung ciia hien tupng
giao thoa:
- Neu khdng quan sat dupc qua trinh
sdng, dua vao hien tupng nao thi cd thi
kit luan dd la qua trinh sdng ?

GV lam thi nghiem dl HS tim hiiu hien
tupng nhilu xa cua sdng.
- T a o ra mdt sdng trdn lan truyin tren
mat nude ciia khay sdng nude. Dimg
2 mieng nhdm nhd d l tao ra mdt khe
hep each hdn bi khoang 5cm. Cho
ddng CO hoat ddng, yeu ciu HS quan
sat va md ta hien tupng xay ra.
GV thdng bao:
- Cang thu hep khe thi hien tupng sdng
lech khdi phuang truyin thing cang rd.

145

Hoat d d n g ciia hgc sinh

Trg giup ciia giao vien
j Neu khe hd cd kich thudc nhd han bUOc
; sdng thi sau khi di qua khe, sdng ed
; dang hlnh trdn gidng nhu chinh khe dd
; la mdt tam phat sdng mdi.
: - Ne'u dat mdt vat can Idn tren dudng
; truyin sdng thi sau khi di qua vat can
; hiu nhu sdng van di thing. Ne'u vat can
: nhd hon budc sdng thi sdng se di vdng
; ra phia sau vat can.

HS tilp thu, ghi nhd.

i

: - Hien tupng sdng khi gap vat can thi di
\ lech khdi phuong truyin thing ciia sdng
; va di vdng qua vat can gpi la su nhilu
; xa cua sdng.
Hoat dong 4
Cung cd bai hgc va dinh hudng
nhiem vu hgc tap tie'p theo

; GV yeu ciu HS lam cic bai tap trie
; nghiem trong phieu hpc tap
; - HS cin dn lai cac kie'n thirc vl am d
Idp 7.
; - HS vl nha lam cac bai tap I, 2, 3, 4

SGK.

PHIEU HOC TAP
Cau 1. Dao ddng cua dilm M tren mat nude la tdng hpp ciia hai dao ddng
dupc truyin den tii hai ngudn cd ciing tin sd, ciing phuang dao ddng
va cd dp lech pha khdng ddi theo thdi gian. Acp la dp lech pha dupc
truyin den tir hai ngudn. Dl M dao ddng vdi bien dp cue tilu thi
A.Acp = kTT iv6ik = 0, ±1,±2,...).
B. Acp = k-

iv6\k = 0, ±1,±2....).

C.Acp = [2k + \)TT iva\k = 0,±\.±2,...).
TT

D. A^ = (2^ + l ) - ivdik = 0, ±1,±2,...).

146


au 2. Hai ngudn sdng 5,, 52 tren mat nude
^
tao ra cac sdng cd budc sdng bing 2m
va bien dp A. Hai ngudn dupc dat
each nhau 4m tren mat nude nhu hinh
|
ve. Biei ring dao ddng cua hai ngudn
Cling pha, ciing bien tin sd va ciing
S,
4(m)

S,
phuang dao ddng. Bien dp dao ddng
tdng hpp tai M each ngudn 5, mdt doan 3m nhan gia tri nao trong cac
gia tri sau day ?
A. 2A.

B. A.

C. 0.

D. 3A.

!au 3. Tren mat nude cd hai ngudn sdng gidng het nhau 5| va 52, hai ngudn
each nhau 18cm. Tin sd dao ddng ciia hai ngudn bing 2077z. Tdc dp
truyin sdng tren mat nude bing \,2mls. So gpn sdng giiia hai ngudn
sdng tren khi cd hien tupng giao thoa xay ra la
A. 5 gpn sdng.
B. 6 gpn sdng.
C. 7 gpn sdng.
D. 8 gpn sdng.
'au 4. Tren mat nude cd hai ngudn sdng gidng het nhau 5, va 52. Khi cd hien
tupng giao thoa xay ra thi dudng trung true ciia doan thing 5|52 la tap
hpp nhiing diem
A. dao ddng vdi bien dp cue tilu.
B. dao ddng vdi bien dp cue dai.
C. dao ddng vdi bien dp cue tieu xen ke nhiing dilm dao ddng vdi
bien dp cue dai.
D. dao ddng vdi bien dp bat ki.
au 5. Tren mat nude cd hai ngudn sdng gidng het nhau 5| va 52, each nhau
10cm. Khi cd hien tupng giao thoa xay ra ngudi ta dem dupc 5 gpn

Idi d giira 5| va 52, va nhirng gpn loi nay chia doan 5|52 thanh 6 doan
ma hai doan d hai diu chi bing mot nira cac doan cdn lai. Budc sdng
tren spi day nhan gia tri nao trong eac gia tri sau day ?
A. A = 2cm.
B. A = 4cm.
CA = 6cm.

D. A = 8cm.

147