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

Hoat ddng cua hgc sinh - Tdc dp truyin sdng dupc xic dinh : v = ^=fX T - Sdng truyin dao ddng cho cac phan tir ciia mdi trudng, nghTa la truyin cho chiing nang lupng.. Ta cd phuang tr

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

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 s i n h T r g 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

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

HS dua ra cae nhan xet khac nhau:

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

HS tie'p thu, ghi nhd khai niem

Trudng hpp a)

- Cae phin tir dao ddng vudng gdc ;

vdi phuang truyin sdng

Hoat ddng ciia hgc sinh Trg giiip cua giao v i i n

HS tie'p thu, ghi nhd khai niem 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

- GiQa eac phin tii cua spi day dan

hdi cd luc dan hdi lien kei chiing

- O thdi dilm ban diu t = 0, tat ca

eic phin tir cua day diu diing ydn

d vi tri 7

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

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 d l HS giai thfch sur tao thanh sdng co

- Giiia cic phin tit cua spi day dan hdi

cd luc lien kei khdng ? Luc dd la luc gi ?

- Hien tupng gi xay ra neu giiia chiing khdng cd luc lien ket ?

- 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 d l 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 ?

- Cac phin tir cang xa tam dao

ddng thi cang tri pha hon cac phin

tir gin tam dao ddng

HS tie'p thu, ghi nhd

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 tir ciia mdi

trudng diu dao ddng vdi cimg chu

kl va tin sd bing chu ki, tin sd ciia

nguon dao ddng gpi la chu ki va

tin sd ciia sdng

- 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 thdng bao:

- 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

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

Hoat ddng cua hgc sinh

- Tdc dp truyin sdng dupc xic

dinh :

v = ^=fX

T

- 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

Hoat dgng 5

Lap phuang trinh sdng, tir dd

suy ra mdt sd' tinh chat ciia sdng

HS suy nghT c i nhan, sau dd thao

luan chung toan Idp

Ta cd phuang trinh dao ddng ciia

dupc truyin tdi diem M nen

phuong trinh dao ddng cua M cd

dang :

Trg giiip cua giao vidn

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

GV neu cau hdi dl HS lap phuang trinh sdng:

- 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:

- Xet sdng truyin dpc theo true Ox, bd

qua luc can d l 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 ?

HS tie'p thu, ghi nhd

Xet dilm tren dudng truyin sdng

cd toa do X = d Thay x = d vao

phuang trinh (1) ta dupc:

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:

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

GV thdng bao:

- Phuang trinh (1) la phuang trinh dao

ddng ciia dilm M ed toa dp x tren phuang truyin sdng tai thdi dilm t gpi

- 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 ?

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

Hoat d d n g cua hgc sinh 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 ?

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 d l ren luyen each lam bai tap trie nghiem khach quan phan 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

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

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

- 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

- 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

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

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 ?

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 ?

Hoat ddng ciia hgc sinh

HS tie'p thu, ghi nhd

HS ehii y quan sat GV tien hanh

thi nghiem va md ta hien tupng

- 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

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

GV tie'n hanh thi nghiem tang tin sd dao ddng dilu hoa ciia mdt diu Id xo hoac mdt diu spi day d l HS quan sat

va yeu ciu HS md ta hien tupng quan sat duoc

"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

Hoat dgng 3 «

Giai thich su tao thanh sdng •

dimg tren sgi day

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 •

Phuong trinh dao ddng cua dilm B \

GV neu cau hdi d l HS giai thich hien tupng:

- Hay giai thich hien tupng thu dupc d tren ?

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 ?

- 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 ?

- Dilm M dao ddng sdm pha hay tre pha hon dilm B ?

- 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 ?

Hoat ddng cua hgc sinh

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

l a :

Ug =-AC0s2TTf, = Ac0s[2TTft-TT)

Sdng phan xa tir B truyin de'n M,

phuang trinh sdng phan xa tai M la :

Trg giup cua giao viin

- 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 ?

- 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 ?

Nlu M khdng dao ddng thi:

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

- 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 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?

GV neu cau hdi gpi y:

- 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

Hoat d d n g cua hgc s i n h

- 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

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

Cling cd bai hgc va dinh hudng

nhiem vu hgc tap tie'p theo

HS lam viec ca nhan, sau dd thao

luan chung toan Idp

Trg giiip cua giao v i e n 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

GV neu eac cau hdi gpi y

- Hai dau spi day la hai mit sdng hay hai bung sdng ?

- Dilu kien d l cd sdng dimg tren spi day la gi ?

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

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

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

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

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:

BAI16

GIAO THOA SONG

I - MUC TifiU

1 Ve k i e n 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 d l kilm tra du doan bing con dudng If thuyei

- Nim dupc dilu kien d l 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) d l md phdng hien tupng giao thoa sdng ca hpc

- Chuan hi bd thi nghiem vl khay sdng nude d l 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

Hoat ddng cua hgc sinh

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 d l cua bai

hpc

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

S, S2

Trg giiip cua giao v i i n

GV neu cau hdi kiem tra kie'n thirc cu:

- Hay van dung phuong trinh sdng d l 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

Giao vien neu cau hdi v l 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 d l HS kilm tra du doan bing con dudng 11 thuyei

- Bing if thuyei cd thi kilm tra du doan tren nhu the' nao?

Hoat d d n g ciia hgc s i n h

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 :

i] = U2 Acos—t A 2;r

T

- Tai dilm M cd hai dao ddng do

hai ngudn sdng truyin de'n la :

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

Trg giiip cua giao v i e n

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

- 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 ?

Nlu dilm M dao ddng vdi bien dp

cue dai thi :

cos Acp

~Y

Acp

• kTT => Acp = 2^;r, suy ra

hai dao ddng dupc truyin de'n tir

hai ngudn 5,, 52 ddng pha

^ Acp = [2k + \)TT, suy ra hai dao

ddng dupc truyin de'n tir hai ngudn

- Nhiing dilm dao ddng vdi bien

dp cue dai cd hieu dudng di :

d2-d] =kA vdi A: = 0,±1,±2,

Thay k = 1, ta ed :

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

- 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

Hoat d d n g cua hgc s i n h T r g giiip cua giao v i e n

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

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

HS tie'p thu, ghi nhd

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

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 d l 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

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

Hoat d d n g ciia hgc s i n h

HS tilp thu, ghi nhd

i

Hoat dong 4

Cung cd bai hgc va dinh hudng

nhiem vu hgc tap tie'p theo

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

: - 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

; 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, )

S, 4(m) S,

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

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

Cau 6 Xet sdng truyin theo mdt spi day cang thing dai Phuang trinh dao

ddng tai ngudn O ed dang : u = Asin2nticm), tdc dp truyin sdng la

25cmls Gpi M va N la 2 dilm gin O nhai lin lupt dao ddng cung pha

va ngupc pha vdi O Khoang each tu O de'n M, N la

- Dinh nghTa dupc Sdng am

- Biet dupc phuong phap thuc nghiem dl khao sat dao ddng am la dimg dao dong

kf dien tir va diu thu micro

- Nim dupc cac dac trung vat If ciia am

- Dl xuai dupc phuang an dung dao ddng kf dien tir, mierd, may phat am tan de tie'n hanh cac thf nghiem nghien ciiu su phu thudc cua cac dac trung sinh ly vao cae dac trung vat li cua am

- Thdng qua TN riit ra dupc dp cao ciia am phu thudc vao tin so: tin so cang Idn thi am phat ra cang cao; dp to ciia am phu thudc vao tin so va miic cudng dp am

- Quan sat cae dang dd thi ciia mdt ngudn am khi giii tin sd khdng thay ddi riit ra kit luan : Cac am cd ciing dp to, dp cao nhung ta vin phan biet dupc cac am dd la

do dang dudng cong bilu diln dao ddng am khac nhau

- Hieu dupc su phu thudc cua dac trung sinh ly ciia am vao cae dac trung vat If (dp cao phu thudc vao tin so, dp to phu thudc vao tin so va miic cudng dp am, am sic phu thudc vao dang dudng bilu diln dao ddng am)

- Phan biet dupc nhac am va tap am; ngudn nhac am chia thanh hai loai: cac loai day dan va cac loai cot khi ciia sao, ken

- Biet dupc vai trd ciia hop cdng hudng trong cac ngudn am

- Ren luyen kT nang quan sat, thu thap va xir ly kei qua quan sat dupe

- Ren luyen kT nang dua ra du doan ddi vdi mdt hien tupng vat li

- Ren luyen kT nang lam viec nhdm

II - C H U X N BI

Giao vien

- 4 am thoa cd biia gd cao su cho 4 nhdm HS

- Mot may dao ddng ky dien tir ; 1 micro; 1 may phat am tan (hoac ngudn dien dilu tan/bien dp hien so) ; bd khueeh dai ; cac ngudn am: nhi, sao, am thoa day ndi; d cim dien

Hpc sinh

- HS can dn lai cac kie'n thiic vl am d Idp 7

III - THifi'T Kfi' H O A T D O N G DAY - H O C

Hoat ddng cua hgc sinh

Trg giiip ciia giao vien

GV neu cau hdi kilm tra kiln thiic cu:

- Dinh nghTa sdng co hpc ? Phan biet sdng ngang, sdng dpc ?

- The' nao la hai ngudn phat sdng ket hpp ? The' nao la hai sdng kei hpp ? Hai sdng kit hpp gap nhau thi tao nen hien tupng gi ?

Dgt vdn de : Chiing ta dang sdng trong

mdt the' gidi am thanh (tie'ng cudi ndi, tie'ng dan nhac du duong, tieng dn ao ngoai dudng pho ) Tai sao ta lai nghe dupc cae am thanh dd? D l tra Idi dupc cac cau hdi nay chiing ta nghien ciiu bai hpc hdm nay

Hoat d d n g cua hgc s i n h

Hoat dgng 2

Tim hieu nguon gdc ciia am :

thanh va cam giac ve am

HS thao luan nhdm, sau dd dai '

dien nhdm len bao cao kei qua

- Khi phat ra am thi cac ngudn am '•

diu dao ddng i

HS thao luan nhdm, sau dd dai ;

dien nhdm len bao kei qua

- Diing biia cao su gd vao mdt ;

nhanh eiia am thoa, ling nghe am ;

do am thoa phat ra

- Lay tay sd vao am thoa thay am i

thoa rung len

- Treo mdt qua bdng ban sat mdt ;

nhanh cua am thoa khi am thoa ;

HS suy nghT ca nhan, sau dc th lO [

luan chung toan Idp ;

- Khi nhanh am thoa dao ddng, •

lam cho Idp khdng khi d ben canh ;

lan lupt bi nen, gian Khdng khi bi ;

Trg giiip cua giao vien

GV neu eau hdi vl vin dl cin nghien

ciiu:

- Khi la thep dan hdi, chudng gid, mat trdng phat ra am, thi cac ngudn am nay cd chung dac diem gi ?

GV neu cau hdi thiei k l phuong an thi nghiem dl kilm tra du doan:

- Hay thiei ke phucmg an thf nghiem de kiem tra du doan tren ?

GV neu cic cau hdi gpi y:

- Cd thi dimg ngudn am la am thoa de lam thi nghiem khdng ?

- Bing each nao d l cd thi kilm tra khi phat am, am thoa dao ddng ?

- Cd thi diing tay cam nhan dupc khdng ?

; - Cd thi dimg qua ciu bac hoac qua bdng ban dl kilm tra dupc khdng ? : GV ban giao thi nghiem cho cac nhdm

; yeu ciu cic nhdm tien hanh thf nghiem

; sau dd dai dien nhdm len bao cio kit

; qua

; GV neu cau hdi vl van d l cin nghien

; ciiu tie'p

1 - Vi sao am thanh tir am thoa phat ra lai

I truyin den tai ta ?

; GV neu cac cau hdi gpi y:

; - Mdi trudng xung quanh am thoa la gi ?

nen, gian truyin cho cae phan tir

khdng khi d xa hon

- Dao ddng dupe truyin di trong

khdng khf, tao thanh Sdng am

(tuang tu nhu sdng nude: vi cd

ngudn am va mdi trudng dan hdi

bao quanh ngudn am.) cd cung tin

sd vdi tan so ciia am thoa Sdng am

truyin qua khdng khi va truyin

den tai ta tac dung vao mang nhT

lam cho mang nhT cung dao ddng

vdi ciing tan so dd Dao ddng ciia

mang nhT lai dupc truyin de'n cac

day thin kinh thinh giac lam cho ta

cd dupe cam giac vl am thanh

Hoat dgng 3

Tim hieu phuang phap thuc

nghiem khao sat nhurng tinh chat

cua am ap dung phuong phap

nay de phan biet nhac am va tap

am

HS thao luan chung toan Idp

- Tuong tu, chuyin dao ddng am

thanh dao ddng dien Tir dd, riit ra

phuang phip : chuyin dao ddng

am thanh dao ddng dien

- Dung cu thf nghiem :

- Dao ddng kf dien tir

- Diu thu mierd

- Khi am thoa dao ddng thi lap khdng khi xung quanh nhanh am thoa se cd hien tupng gi ?

- Su nen gian ciia Idp khdng khi xung quanh am thoa cd dupc truyin ra mdi trudng xung quanh khdng ?

- Tai sao tai ta cd cam giac am ?

GV neu cau hdi dl HS tim hiiu phuang phap thuc nghiem khao sat nhiing tfnh chit ciia am:

- Hay dua ra phuong phap ghi lai dang

dd thi dao ddng am?

GV neu cau hdi gpi y:

- Khi ca sT hat trudc mierd, ndi trudc d'ng ndi ciia may dien thoai, thi tin hieu

am chuyin thanh tin hieu dien Lieu cd thi ghi lai dang dd thi am bing each nao ?

- Cd thi diing dao ddng kf dien tir dl ghi lai dang dd thi am dupc khdng ? Ne'u dupc thi can nhirng dung eu thi nghiem nao ?

GV tiln hanh thi nghiem dl HS quan sat

Hoat ddng ciia hgc sinh

HS chii y quan sat

HS chii y quan sat va thao luan

chung toan Idp

- Do thi ciia am do am thoa hoac

cac ngudn nhac am phat ra la

nhiing dudng cong tuan hoan cd

tin sd xac dinh

- Dd thi ciia am do tie'ng gd manh

tren tam kim loai la dudng cong

khdng tuan hoan va khdng cd tan

- Lan lupt sir dung eac ngudn am khac nhau (am thoa, ken, tie'ng go len tam kim loai va ngudn am diing mach IC), quan sat dudng bilu diln dao ddng am ciia tung ngudn am tren dao ddng kf

Luu y : Ne'u khdng cd logi micro nhgy thi phdi diing bg khueeh dgi ndi vdi micro

GV yeu ciu HS so sanh hinh anh thu dupc tren dao ddng kf dien tir dd thi eiia

am do am thoa, tie'ng gd manh tren tim kim loai, am do nhac cu phat ra

Am thoa Tie'ng go manh

tren tam kim loai

HS tilp thu, ghi nhd

- Am do cae nhac cu phat ra thi em ai,

dl chiu va dd thi dao ddng cua chiing cd dac dilm chung la nhirng dudng cong tuin hoan cd tin so xac dinh Chiing dupc gpi la nhac am

- Nhiing am thanh nghe chdi tai, gay cam giac khd chiu, dd thi cua chiing la nhirng dudng cong khdng tuin hoan, khdng cd tin sd xac dinh Chiing dupc gpi la tap am

GV neu cau hdi d l HS tim hiiu cac dac trung vat If cua sdng am:

- Qua trinh truyin am cQng la mot qua trinh truyin sdng Vay sdng am cung phai cd cae dac trung vat If ciia sdng, dd

la nhiing dac trung nao ?

GV thdng bao mdt so dac trung vat li ciia am:

Hoat ddng cua hgc sinh

HS tie'p thu ghi nhd

Trg giiip cua giao vien

- Nang lupng am : La nang lupng dao ddng ciia cae phan tir vat chai ciia mdi trudng truyin am (E ~ A^)

- Cudng dp am 7 : la nang lupng sdng

am truyin qua mdt don vi dien tich dat vudng gdc vdi phuang truyin sdng trong mdt don vi thdi gian ( 7 ~A )

fV Dan Vl: —-

7 : cudng dp am tai dilm dd Don v i : Ben (5),

Thutog diing don vi la dB (dexiben) : , 15 = lOdB

\ GV gpi lai kinh nghiem ciia HS thdng

\ qua cac vf du, dl HS cd dupc hieu biei

\ ban dau vl dp cao cua am:

• - Trong ddi sdng vin thudng ndi

; Gipng nii cao, gipng nam trim

Gipng ndi cua ngudi dupc md ta bing

; nhilu tinh tir : d 1, im, lanh lanh, the

; the., vdi mdi trudng hpp hay nhan dinh

; vl tin sd am tuong ling?

GV thdng bao khii niem vl dp cao cua

; am:

i - Dp cao la dac trung sinh If d l phan

; biet am cao (bdng) vdi am thap (tram)

HS thao luan nhdm, sau dd dai

dien nhdm len bao cao kei qua

Cac nhdm dua ra du doan:

- Dp cao phu thudc vao tan so,

bien dp dao ddng am

- Dp cao phu thudc vao tin so

- Dp cao phu thudc vao bien dp

dao ddng am

HS thao luan nhdm, sau dd dai

dien nhdm len bao cao kei qua

- Diing mdt ngudn am lay tin hieu

tir ngudn dien dilu tin, dung dao

ddng ki dien tir va mierd ghi lai dd

thi dao ddng am, thay ddi cac dac

trung vat ly xem dp cao thay ddi

the nao

- Trong trudng hpp dua ra du

doan : dp cao phu thudc vao ddng

thdi hai yeu td nhu tren, ta se giir

nguyen mdt ye'u td, thay ddi yeu td

con lai xem dp cao phu thudc vao

ylu td dd nhu the' nao

HS ling nghe va riit ra kei luan:

- Dp cao khdng phu thudc vao

GV neu cau hdi thiei ke' phuong an thi nghiem kilm tra:

- Hay thiei ke' phuang in thi nghiem dl kilm tra du doan tren

GV neu cau hdi vl each tien hanh thi nghiem

- Cin phai tien hanh thi nghiem nhu thi nao dl kilm tra dupc 3 du doan tren ?

GV thdng bao:

- Trong thf nghiem nay ta nhan bilt sir thay ddi tin sd ciia loa bing each dpc ngay gia tri tin so tren ngudn dien dilu tin ma khdng cin phai dua vao dao ddng kf dien tir Ngudn dien dilu tin cho phep ta thay ddi dupc tin so, va am lupng eiia am phat ra (bien dp) GV kei hpp chi niim dilu cho HS quan sat

GV tie'n hanh thf nghiem, yeu ciu HS ling nghe dp cao do am phat ra trong eac trudng hpp khi tang din bien dp dao

Hoat ddng cua hgc sinh

- Am cd /3 = 1 lOOHz phat ra cao

han so vdi am cd tan so /2=

120077Z

- Am cd tin sd/2 = 120077z phat ra

cao han so vdi am cd tin s o / , =

90077Z

Dp cao phu thudc vao tin so cua

am: Tan sd Idn nghe tha'y am cao,

tin so thap nghe thay am trim

HS tie'p thu, ghi nhd khai niem

HS thao luan nhdm, sau dd dai

dien nhdm len bao cao kei qua

Trg giup cua giao vien

ddng, rdi riit ra nhan xet vl sU phu thudc eiia dp cao vao bien dp dao ddng?

Lan 1 : gi{r/= 90077z tang din bien dp dao ddng

GV tie'n hanh thf nghiem, yeu ciu HS ling nghe dp cao do am phat ra trong cae trudng hpp dd rdi riit ra nhan xet vl sir phu thudc eiia dp cao vao tin sd ? Lin 2 : giir nguyen bien dp dao ddng, thay ddi tin sd l i n lupt : 90077z, 120077Z, 170077Z

GV gpi lai kinh nghiem cua HS thdng qua cac vi du, dl so bd HS biei dupc khai niem dp to cua am, va dl xuit du doan vl su phu thudc cua dp to vao cac dac trung vat If cua am

- Ong, ba cao tudi thudng nghe kem Khi mud'n ndi d l cho dng, ba nghe ro hon, em lam the' nao ?

- Gipng ndi cua con ngudi dupc diln ta bing nhilu tfnh tii : thiu thao, thu thi,

em ai, oang oang Vdi mdi trudng hop hay neu nhan dinh vl dp to cua am ?

- Khi ha gipng d l ndi nhd lai hay len gipng dl ndi to, am phat ra da thay ddi dai lupng nao ?

GV thdng bao khai niem vl dp to cua am:

- Dp to la dac trung sinh Iy cua am cho chiing ta cam giac nghe tha'y am to hay nhd

- Dp to phu thudc vao tin sd, bien

dp dao ddng am

- PA kilm tra : Dung ngudn dien

dilu tin bien dp hien so, dao ddng

ki dien tir va diu thu micro ghi lai

do thi dao ddng am, lan lupt thay

ddi cac dac trung vat If xem dp to

thay ddi nhu the nao

HS quan sit, ling nghe va riit ra

kei luan:

- Dp to phu thudc vao bien dp dao

ddng am, bien dp dao ddng cang

Idn thi dp to ciia am cang Idn

- Vi cudng dp am ti le vdi bien dp

dao ddng, ma ddi vdi mdi mdt am

phat ra IQ la khdng thay ddi do dd,

mire cudng dp am ti le vdi bien dp

dao ddng suy ra: Dp to ciia am

phu thudc vao miic cudng dp am

- Vdi cic am cd tin sd khic nhau

thi cung cho ta cam giac nghe thay

am to nhd khac nhau

Ke't ludn : Dp to cua am phu thudc

vao tan sd va miic cudng dp am

HS tie'p thu, ghi nhd

GV neu cau hdi vl van d l cin nghien ciiu tie'p:

- Dp to ciia am phu thudc vao dac trung vat If nao va phu thudc nhu the' nao vao cac dac trung vat If dd ?

GV neu cau hdi thiei ke' phuang an thi nghiem kilm tra:

- Hay thiei ke' phuong an thf nghiem dl kilm tra du doan tren ?

GV tie'n hanh thf nghiem, yeu ciu HS quan sat va chii y ling nghe dl riit ra kei luan

- Lin 1 : giii nguyen tin so, thay ddi bien dp dao ddng ciia am phat ra, phan biet dp to cua am nghe dupc khi thay ddi bien dp

- Dp to ciia am cd phu thudc vao mire cudng dp am hay khdng ?

- Lin 2 : giir nguydn bien dp dao ddng, thay ddi tin so ciia am phat ra, phan biet

dp to cua am nghe dupc khi thay ddi tin so

GV thdng bao khai niem am sic:

- Ciing mdt bai hat tiic la cd cimg dp cao, nhung do cac ea sT khac nhau thi hien tai sao ta vin phan biet dupe gipng

Hoat ddng cua hgc sinh

HS thao luan chung toan Idp

- Vi do cae ngudn am khac nhau

phat ra

HS chii y quan sat va riit ra kei

luan:

- Cae am nghe dupc khac nhau la

do dang dudng bilu diln dao ddng

am khac nhau

Trg giiip cua giao v i e n

hat ciia timg ngudi, dd la dac trung sinh

ly nao ciia am quyei dinh?

- Am sic la dac trung giiip ta phan biet dupe hai am cd cung dp cao, dp to nhung do cae ngudn am khac nhau phat ra

GV neu cau hdi vl van d l cin nghien ciiu tie'p:

- Tai sao cic am cd cimg dp cao, dp to

ma ta vin phan biet dupe cae am dd ?

GV ndu cac cau hdi gpi y:

- Ngoai dac dilm cua cac ngudn am khac nhau, cdn yeu td vat If nao quyei dinh niia khdng? Neu cac am do mdt ngudn phit ra trong cac trudng hop khac nhau thi sao ?

- Neu bay gid tdi dua cac tin hieu am nay cd ciing dp cao, dp to vao dao ddng

ky dien tir cac em hay quan sat dang dd thi bilu diln dao ddng am va ling nghe

am phit ra trong cac trudng hop dd, rdi riit ra nhan xet

GV gidi thieu thf nghiem va each tie'n hanh thf nghiem, sau dd tien hanh thi nghiem dl HS quan sit va riit ra kei luan:

- Trong trudng hop nay thay vi dung hai ngudn am khac nhau cd ciing dp cao, dp to, ta se dung mdt ngudn am (ngudn dien dilu tan bien dp hien sd ndi vdi loa) va giii nguyen tan sd, dp to eiia

am phat ra

Ket ludn : Cac am cd ciing dp cao, ;

dp to nhung cd am sic khac nhau ;

la do dang dudng cong bilu diln i

su bie'n thien cua li dp dao ddng ;

am theo thdi gian khac nhau ;

Hoat dgng 6

Tim hieu gidi han nghe cua tai |

con ngudi

HS tie'p thu, ghi nhd '•

HS thao luan chung toan Idp:

- Ngudng nghe phu thudc vao tin I

sd ;

HS tie'p thu ghi, nhd

— GV lam TN giu nguyen dp cao (tin so), dp to cua am do loa phat ra, nhung thay ddi dang tin hieu dua ra man hinh dao ddng ki (dang xung sin, xung vudng

va xung tam giac)

GV thdng bao:

- Do dac dilm sinh If eiia tai, dl gay dupc cam giac am thanh thi cudng dp

am phai Idn hon mdt gia tri cue tilu nao

dd gpi la ngudng nghe

- Ngudng nghe : La cudng dp am nhd nhat cho ta cam giic vl am

GV neu cau hdi d l HS tim hiiu vl ngudng nghe cua tai con ngudi:

- Ngudng nghe phu thudc vao dac tinh vat 11 nao ?

- Thdng qua so lieu, hay cho biei ngudng nghe phu thudc vao ye'u to nao ?

- Ne'u cudng dp am len den lOWIm thi

dd'i vdi mpi tin so, sdng am se gay ra mdt cam giac nhiic nhdi, dau ddn khdng cdn cam giac am binh thudng niia, gia tri nay cua cudng dp am gpi la ngudng dau

Hoat d d n g cua hgc s i n h

Hoat dong 7

Tim hieu ve hai nguon nhac am: :

day dan va dng sao

HS thao luan chung toan lop: •

- Khi chilu dai soi day: I = n— thi ;

2 ; tren spi day xuai hien hien tupng ;

sdng dimg 1

Ta cd td'e dp truyin sdng tren spi |

day dupc xac dinh : v = f.A ;

nv '

Suy ra: f = •

2/ ;

- Tin so am ti le thuan vdi so bung :

sdng tren spi day •

HS tie'p thu, ghi nhd

Trg giup cua giao vidn

- Ngudng dau : la gia tri cue dai cua cudng dp am ma tai ngudi cd thi chiu dung dupe vl am dd

- Miin nim giira ngudng nghe va ngudng dau gpi la miin nghe dupc

GV neu cau hdi dl HS tim hiiu vl hai ngudn nhac am:

- Khi day dan cd hai dau cd dinh phat

ra am thanh thi trdn day dan xuit hien hien tupng gi ? Khi dd, tan sd cua am dupc xac dinh bing bilu thiic toan hpc nao ?

GV neu cau hdi gpi y:

- Dilu kien d l xuat hien sdng dimg tren spi day cd hai dau cd dinh?

- Tdc dp truyin sdng tren spi day dupc xac dinh bing bilu thiic nao ?

- Suy ra bilu thiic xic dinh tin sd ciia

am phat ra?

- Nhan xet vl su phu thudc cua tin sd

am phat ra vao so bung sdng tren day ?

HS thao luan chung toan Idp

Dilu kien dl xay ra hien tupng

sdng dimg dd'i vdi cdt khf trong

n = 2, /2 = - ' tren day cd 2 bung va 3

nut Khi dd am phat ra gpi la hoa am

3v bac 2; vdi « = 3, /3 = — am phat ra gpi la hoa am bac 3

- Mdi day dan dupe keo cang bing luc cang cd dinh ddng thdi cd thi phat ra

am CO ban va mdt sd hoa am bac cao hon, cd tin sd la mdt sd nguyen lin tin

sd ciia am co ban Tren day lan truyin ddng thdi nhilu dao ddng dilu hoa cd tin so la sd nguyen lan tin sd ciia am co ban Tdng hpp nhiing dao ddng dd ta dupc mdt dao ddng tuin hoan phiie tap

cd ciing tin sd vdi am co ban Vl vay, hai nhac cu ciing phat ra mdt am co ban, nhung cd cac hoa am khac nhau thi am tdng hpp se cd cimg tin sd nhung cd dang dd thi dao ddng khac nhau nen cd

am sic khac nhau

GV neu cau hdi dl HS tim hieu vl ngudn nhac am la d'ng sao:

- Tin sd am do d'ng sao cd mdt diu bit' kin phat ra dupc xac dinh bing bilu thirc toan hpc nao ?

GV neu cae cau hdi gpi y:

- Dilu kien dl xay ra hien tupng sdng dimg dd'i vdi cdt khi trong d'ng sao ?

- Suy ra tin sd am co ban va cac hoa

am

Hoat ddng cua hgc sinh

Suy ra tan so am phat ra ciia dng

sao la :

mv

" ^

Tan so am co ban img vdi m = 1 la:

Hoa am bac 3 ling vdi m = 3 la :

•^' - 41

Hoa am bac 5 ling vdi m = 3 la :

Hoat dong 8

Tim hieu ve hop cdng hudng

HS thao luan chung toan Idp:

- Trudng hpp cd gin vao hop rdng

am phat ra se to hon

- Lam TN kilm tra

- Tang cudng phat am ra

HS tie'p thu, ghi nhd

Trg giiip ciia giao vidn

GV neu cau hdi d l HS tim hiiu hop cdng hudng:

- Ne'u bay gid tdi dirng biia cao su go vao mdt nhanh am thoa khdng gin vao hop gd rdng va trudng hpp cd gin hop

gd rdng, trong trudng hpp nao am phat

ra to han ?

GV phat dung cu thi nghiem cho cac nhdm, yeu ciu HS tien hanh thf nghiem kilm tra

- Hop rdng dd gpi la hop cdng hudng, hop cdng hudng cd tac dung gi ?

- Giai thich vai trd cua hop cdng hudng dd'i vdi cac ngudn nhac am ?

GV thdng bao:

Am do cac dung cu true tiep phat ra co

cudng dp rai be De am phat ra to ngUdi

ta phai diing ngudn am dd kfch thfch