Giáo trình vật lý đại cương phần 2 (dành cho sinh viên đh chính quy ngành y dược)

Dinh luat bao toan dien tich Cac hien tupng v6 dien luon luon tuan theo dinh luat bao toan dien tfch: Cac dien tich khdng the tit nhien sinh ra, cung khong tit bien ma't, no chi cd the t

P h a n thCr b a

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Chuong 1

1 Khai niem m d dau

1.1 Sir nhi£m dien do co sat

Tir the ky VI trudc cong nguyen, ngudi ta da nhan thay khi dem co sat thuy tinh, ebonit va mot so vat khac vao len da, thi thuy tinh, ebonit co kha nang hut cac vat nhe nhu giay vun, long chim Hien tupng do goi la hien tupng nhiSm dien do co sat Thuy tinh, ebonit dupe goi la vat nhiim dien

Qua su nhiim dien do co sat, nguai ta thay chi xuat hien 2 loai dien tfch:

- Loai dien tfch xuat hien giong nhu a thuy tinh khi co sat vao len da goi la dien tfch duang (+)•

- Loai dien tfch xuat hien nhu d thanh ebonit khi co sat vao len da goi la dien tfch am (-)

Qua thuc nghiem con thay cac loai dien tfch tuang tac vai nhau: hai dien tfch cung dau thi day nhau, khac dau thi hut nhau

1.2 Sa lirac ve thuyet dien tir

Qua nhieu thi nghiem cac nha bac hoc da di den ket luan:

- Dien tfch tren mot vat mang dien bat ky co cau tao gian doan, no luon luon bang mot sd nguyen lan cua mot dien lupng nhd nhat goi la dien tfch nguyen to: dien tfch nguyen to cd gia tri |q0| = 1,6.10'19C Cac hat mang dientfch nguyen to cd electron mang dien tfch nguyen to am, proton mang dien tfch nguyen to duang

- Proton va dien tir (electron) deu cd trong thanh phan cau tao nguyen tir cua moi chat Proton nam d hat nhan nguyen tir, dien tir chuyen dong xung quanh hat nhan

- 6 trang thai binh thudng so proton va dien tir cua mot nguyen tir luon luon bang nhau (bang sd thu tu Z cua nguyen to trong bang tuan hoan Mendeleep), ta ndi nguyen tir trung hoa ve dien Neu vi ly do nao dd nguyen tir mat thu them dien tir se trd thanh mot phan tir mang dien Neu mat dien tir nguyen tir se mang

97

dien duong goi la ion (+), neu thu them dien tir nguyen tir trd thanh mang dien am goi laion (-)•

Hoe thuyet can cu: vao chuyen dong cua dien tir de giai thfch cac hien tuong

ve dien goi la thuyet dien tir

1.3 Dinh luat bao toan dien tich

Cac hien tupng v6 dien luon luon tuan theo dinh luat bao toan dien tfch: Cac dien tich khdng the tit nhien sinh ra, cung khong tit bien ma't, no chi cd the truyen tit vat nay sang vat khac hoac phan nay sang phan khac ciia vat.

Noi mot cach khac: Tong dai so cac dien tich trong mot he cd lap Id khdng doi

Thf du: Khi co sat thuy tinh vao len da, neu thuy tinh mang dien duong thi dien tir tir thuy tinh da mat di, co nghla la no phai chuyen sang len da, do do len

da phai mang dien am Do ldn dien tfch tren hai vat luon luon bang nhau neu trudc dd hai vat d£u chua mang dien

1.4 Vat d in dien, vat cach dien

1.4.1 Vat ddn dien

La nhung vat ma dien tfch cd the chuyen dong tu do trong toan bo the tfch cua vat Thf du nhu kim loai, cac dung dich dien phan, chat khf da bi ion hoa, cac

co the song

1.4.2 Vat cach dien (dien mdi)

La cac vat ma dien tfch khdng thi chuyen dong tir diem nay den didm kia

cua vat (khdng cd dien tfch tu do) Thf du: Thuy tinh, ebonit, cao su, gd, khdng khf kho

C hi y: Su phan chia ra vat din dien va each dien chi cd tfnh chat quy udc

Thuc vay trong nhung dieu kien nhat dinh vat nao cung cd the dan dien dupe, chung chi khac nhau la do dan dien nhieu hay ft Khi thay ddi dieu kien thi tfnh dan dien thay doi Thf du: thuy tinh d dieu kien binh thudng dan dien rat yeu (khong dan dien) nhung d nhiet do cao cd the dan dien

Ngoai ra, cd mot nhom chat cd tfnh chat dan dien trung gian giua vat dan

dien va dien mdi Dd la cac chat ban dan.

Trong chuong nay chi nghien cuu tuong tac va tfnh chat ciia cac dien tfch dung yen (so vdi he quy chieu dung de nghien cuu dien tfch dd)

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2 Djnh lu at Culdng (Coulomb)

Nhir ta da biet cac dien tfch tuang tac vai nhau: cung dau thi day nhau, khac dau thi hut nhau Tuang tac giua hai dien tfch durng yen goi la tuong tac tinh dien (hay la tuong tac Culong)

Nam 1875, Culong nha bac hoc nguai Phap bang thuc nghiem da xac djnh duoc luc tuong tac giua hai dien tfch diem

2.1 Dien tich diem

La nhung vat mang dien co kfch thuoc nho khong dang ke so v6i khoang cach tur diem do den nhung diem hoac nhung vat mang dien khac ma ta dang khao sat Nhu vay, khai niem dien tfch diem chi co tfnh chat tuong doi, tuong tu nhu khai niem chat diem trong co hoc

2.2 Djnh luat Culong trong chan khong

Gia sir co hai dien tfch diem q,, q2 dat trong chan khong cach nhau mot

khoang r Dinh luat Culong phat bieu nhu sau: Luc tuang tac giua hai dien tich diem co phuong nam tren dudng thdng noi hai dien tich, co chieu: 2 dien tich cung dau thi day nhau, 2 dien tich khac dau hut nhau (hinh 1.1) Co do Ion ty le thuan voi tich so do Ion cua hai dien tich,

ty le nghich voi binh phuong khoang cach

giua hai dien tich do.

trong do k la he so ty le Trong he SI:

k = —— ; s0 duoc goi la hang so dien, co gia tri:

4tie

e0 — 8,86.10 (N C m )

k = 9.109 (N C 2m2)

Ta co the bieu diin dinh luat Culong dudi dang vecto nhu sau:

Ke vecto r goc q, ngon q2 thi:

Thuc nghiem cung chting to neu hai dien tich diem dat trong chat dien moi

co cung khoang cach nhu khi chting dat trong chan khong thi luc tuong tac se giam di e lan

Cong thtic (1) se la:

12 47t£0.£ r2 rtrong do, £ dupe goi la hang so dien moi phu thuoc vao ban chat cua dien moi, nhiet do

Thi du: Trong chan khong £ = 1

Khong khf: e = 1,006 «1

Nude £ = 81

Chu y: Dinh luat Culong mdi chi cho ta xet tuong tac giua hai dien tich

diem Tuy nhien neu ap dung nguyen ly tong hop luc trong co hoc, ta cd the xet tuong tac giua hai vat mang dien bat ky That vay:

- Neu he gdm nhieu dien tfch diem q b q2, qn phan bo gian doan trong khdng gian va mot dien tfch q0 dat trong khdng gian dd Ta xet tuong tac tting he

2.3 Dinh luat Culong trong cac moi trudng

3 Dien trtfdng cua cac dien tfch diem

3.1 Khai niem ve dien trudng

Ta da biet cac dien tfch tuong tac vdi nhau ngay ca khi chung dat trong chan khdng CJ day cd the dat ra nhieu cau hoi: Luc tuong tac dd truyen di nhu the nao?

Co can mdi trudng xung quanh khdng? Khi chi cd mot dien tfch thi mdi trudng xung quanh cd gi thay doi?

100

D e tra lai cac cau hoi tren trong qua trinh phat trien cua vat ly hoc da co hai gia thuyet doi lap nhau: Thuyet tac dung xa, thuyet tac dung gan.

T heo thuyet tac dung xa, dien tfch tuang tac vai nhau khong can m ot m oi trudng trung gian m a no duoc truyen tijr dien tfch nay den dien tfch kia m ot cach tuc thai vai van toe vo cung lan Cung theo thuyet nay neu chi co m ot dien tfch thi m oi truang xun g quanh dien tfch do khong bien doi gi Thua nhan thuyet tuang tac (tuc la truyen van d on g) khong can thong qua vat chat, thuyet tac dung

xa da thua nhan co van dong phi vat chat do do thuyet nay da bi bac bo.

Trai vai thuyet tac dung xa, thuyet tac dung gan ch o rang xun g quanh m 6i dien tfch co xuat hien m ot dang vat chat “dac biet” g o i la dien truang N h d dien truang, cac dien tfch m oi tuong tac duac vai nhau, van toe truyen phai la huu han

M ot tfnh chat c o ban cua dien trudng la khi dat m ot dien tfch trong dien truang thi deu bi dien truang tac dung luc.

K hoa hoc hien dai da chung m inh thuyet tac dung gan la dung.

V ay xung quanh dien tfch dung yen xuat hien m ot dien truang D ien truang la

m ot dang cua vat chat.

3.2 Vecta cudng do dien truang

3.2.1 Dinh nghia

Gia su' c o m ot d ien tfch q0 dat tai m ot diem trong dien trudng D ie n tfch qn rat nho de no kh on g lam thay doi dien truang m a ta dang x et, dien tfch q„ duac goi la dien tfch thu (q ()> 0).

Thuc ngh iem chu n g to:

F

q0

doi vai m ot d ilm x ac dinh E duac goi la vecto' cud n g do dien trudng.

Vay: Vecta cudng do dien trudng tai mot diem Id mot dai luong vecto co gia tri bang luc cua dien trudng tac dung len mot dan vi dien tich duong dat tai do.

V i vay v e c to cud n g do dien trudng dac trung ch o dien trudng ve phuang dien tac dung luc.

Trong he SI dan vi cua E la (V m ').

3.2.2 Vecto cudng do dien trudng gay ra boi mot dien tich diem

G ia su c o m ot dien tfch diem q X ung quanh q co m ot dien trudng Tai m ot diem M cach q m ot kh oang r neu ta dat dien tfch q() T heo dinh luat C ulon g, lire tac dung cua dien trudng q len q0 la:

F — 1 q gp r

47re0.e r2 r

q0 4.7t.s0.8 r r

47i.e0.e r

3.2.3 Vecta cudng do dien trudng do he dien tich diem

Gia su co he dien tich diem q,, q2, qn Tai mot diem M trong dien trudng

do he dien tfch diem tren gay ra neu ta dat dien tfch thu q0

3.3 Luong cuc dien

3.3.1 Dinh nghia

Ludng cuc dien la he hai dien tich diem cd dien tich bang nhau vd trai da'u (+q, -q) cach nhau mot khoang I rat nho so vdi khoang cach tif ludng cuc dien tdi diem dang xet.

De dac trung cho ludng cuc dien, ngudi

ludng cuc dien, duoc dinh nghla:

trong do, q la do ldn cua mdi dien tfch

J duoc ke tir - q den +q

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Dudng thang noi giua q va -q duoc goi la true luong cuc dien.

3.3.2 Dien trudng do ludng cuc dien gay ra

De don gian ta chi xet cuong do dien truong do luong cuc dien gay ra tai nhung diem nam tren duong trung true cua /, each / mot khoang r » /

Theo nguyen ly ch6ng chat cua dien truong ta co:

3.3.3 Ludng cuc dien trong dien trudng

Gia su cd mot ludng cuc dien dat trong

dien trudng deu, vecto cudng do dien

trudng E lam vdi Pc mot goc a Cac dien

tich +q va -q se chiu mot luc tac dung cua

* Chu y:

- Trang thai can bang cua ludng cuc dien con phu thuoc vao chuyen dong nhiet cua cac phan tir luong cuc

- Neu luong cuc khong vung chac thi trong qua trinh quay, no co thi bi bien dang

* ling dung thuc te: Nau nudng bang lo vi song Mot phan tu nuoc (H20 ) la

mot luong cuc dien Oxy va 2 nguyen tu hydro lien ket vdi nhau khong nam tren cung mot duong thang ma tao thanh mot goc chung 105° (hinh 1.6)

Ket qua la phan tu nude

cd hai phfa xac dinh, phfa oxy

va phfa hydro Ngoai ra 10

dien tu trong phan tu nude cd

xu hudng d gan hat nhan oxy

hon gan hat nhan hydro

Dieu do lam cho phan tu

nude tao thanh mot ludng cue

dien, phfa duong la hydro,

phfa am la oxy

Trong*nudc, khi cac phan tu cd the chuyen dong tuong ddi, dien trudng do mdi ludng cue dien sinh ra anh hudng den cac ludng cue dien xung quanh Ket qua la cac phan tir nude cd the lien ket thanh nhom 2 hoac nhom 3 phan tu (hinh 1.6) (vi dau am cua phan tu ludng cue nay hut dau duong cua phan tu ludng cue khac)

Mdi lan hinh thanh mot nhom nhu vay, the nang dien dupe chuyen thanh dong nang chuyen dong cua cac phan tu' Va mdi lan va cham khi mot nhom tan

ra thi nang lupng lai chuyen theo chieu nguoc lai Nhiet do ciia nude khdng thay doi vi trung binh su chuyen doi nang lupng tong cong bang khdng

Khi lo vi song hoat dong, cac song micromet tao ra trong lo dien trudng xoay chieu (vdi cac lo vi song pho bien hien nay tan so f = 10l4Hz)

Neu trong lo cd H20 , cac phan tu ludng cue nude quay tdi, quay lui mot each lien tuc de dinh hudng md men ludng cue dien theo dien trudng Cac phan tu ludng cuc lien ket thanh cap cd the quay quanh mdi lien ket chung, chung cd thi dinh hudng theo dien trudng Tuy nhien, trong cac lien ket nhom 3 ft nhat mot phan tir bi gay trong nhom lien ket va luc dd giai phdng nang lupng dudi dang nhiet, nude nong len

Vay trong lo vi song nang lupng song dien tir da chuyln thanh nhiet nang

Hinh 1.6

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4 Dien the Hieu dien the■ ■ •

4.1 Cong cua lire dien truong

Gia su co mol dien tfch +q Xung quanh +q

co mot dien truong Ta hay tfnh cong cua

lire dien truong lam q0 dich chuyen tu A

den B theo mot dudng bat ky

Nhan xet: Cong cua lire dien truong khong phu thuoc vao hinh dang duong

di, chi phu thuoc vao vi tri cac diem dau va diem cuoi Vi vay, dien truong cung

la mot truong the va luc dien la mot luc the

4.2 The nang dien tich diem trong dien trucmg

Ta da biet doi vai trucmg the

Tong quat: The nang cua mot dien tfch diem trong dien truang tai mot vi trf

cach q mot khoang r la:

W, = — -— M l + c

4.7l.£0£ r

C la hang so tuy y chon Tuy nhien, trong thuc te ta khong tfnh the nang ma chi tfnh hieu the nang nen hang so C don gian ta chon bang 0

Thi r5 rang V khong phu thuoc vao q() chi con phu thuoc vao dien tich q gay

ra dien truong va r tmh tfir vi trf xet V dupe goi la dien the

Neu co he dien tfch diem:

1

v - E Y - i - x i

i= l 4.7T.£0£ ,=1 r

Trong he SI, don vi cua dien the la Von (V)

4.4 Hieu dien the

Voi khai niem hieu dien the thi cong cua luc dien truong co the viet:

do Do do, hieu dien the dac trung cho dien truong ve kha nang sinh cong

Ro rang dien the va hieu dien the cung don vi do (Von)

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DONG DIEN KHONG DOI■

Chuong 2

1 Nhufng khai niem md dau

1.1 Dinh nghla dong dien

Trong moi truong dan dien cac dien tich tu do luon luon chuyen dong h6n loan Dudi tac dung cua dien trudng ngoai cac dien tich tu do do se chuydn dong

co huong: dien tfch duong chuyein dong cung chieu dien trudng, dien tfch am

chuyen dong nguoc chieu dien trudng Ddng cac hat dien tich chuyen dong cd huong dudi tac dung ciia dien trudng goi la ddng dien.

Theo quy udc, chieu cua ddng dien la chieu chuyen ddi cua cac hat dien tich duong hay la nguoc chieu vdi chidu chuyen dong cua cac hat dien tich am

1.2 Ban chat dong dien trong cac moi trudng

Ban chat ddng dien trong cac mdi trudng khac nhau cung khac nhau (hinh 2.1).Thuc vay nhu ta da biet trong kim loai, cac nguyen tu lien ket chat che vdi nhau tao thanh mang tinh the kim loai Cac ion duong chi dao dong xung quanh nut mang, ddng cac dien tu tu do (electron tu do) chuyen dong hdn loan trong khdng gian giua cac nut mang Dudi tac dung cua dien trudng, chfnh cac dien tu tir do nay chuy6n dong tao ra ddng dien (hinh 2.1a)

tac dung cua dien trudng cac ion nay chuyen dong tao ra ddng dien (hinh 2.1.b) Khoi luong m cua chat dupe giai phong ra d dien cuc binh dien phan dupe tmh theo cdng thuc:

/ * 1 A i m(g) = - —.It

F ntrong do: F la mot hdng so goi la so Faraday: F = 96500C/mol,

A la khoi lupng mol nguyen tir cua chat thu dupe d dien cuc

Ddi vdi chat khf d trang thai binh thudng, cac phan tir khf hau nhu deu a

trang thai trung hoa ve dien Tuy nhien, khi cd kfch thfch ben ngoai, cac phan tir khf cd the giai phdng dien tir thanh ion duong Cac dien tir dupe giai phdng, mot

so d trang thai tu do, mot sd ket hop vdi nguyen tir trung hoa khac thanh ion am Khi cd dien trudng ngoai ca ion duong, ion am, dien tir deu chuydn dong tao ra ddng dien (hinh 2.1 c)

Chan khdng von khdng cd hat mang dien No chi ddn dupe dien khi dua electron vao Ddng dien trong chan khdng la ddng chuyen ddi cd hudng ciia cac electron but ra tir catot bi nung nong do tac dung ciia dien trudng Dac diem cua ddng dien trong chan khdng la no chi chay theo mot chieu nhat dinh tir anot sang catot

Ddng dien trong ban ddn la ddng dich chuyen cd hudng ciia cac electron tu

do va Id trong dudi tac dung ciia dien trudng Tuy theo tap chat pha vao ban ddn tinh khiet ma ban ddn thuoc mot trong hai loai la ban ddn loai n va ban ddn loai p Ddng dien trong ban ddn loai n chii yeu la ddng electron, con trong ban ddn loai p chu yeu la ddng cac Id trong

1.3 Tac dung cua dong dien

Tuy cd ban chat khac nhau nhung ddng dien bao gid cung cd tac dung dac trung giong nhau nhu tac dung nhiet, tac dung tir, tac dung sinh ly, tac dung co hoc Cac tac dung nay dupe ung dung nhieu trong y hoc

2 INI h urng dai luong dac trurng cua dong dien

Tir do suy ra dien lupng q di qua dien tfch S

trong thoi gian t se la:

t t

Neu i co phuang, chieu, do lan khong d6i

theo thai gian thi dong dien do dupe goi la dong

dien khong doi tir (2) neu i = I = const, ta co:

t

q= Ji.dt=I.t (3)

oTrong he SI, dan vi cuang do dong dien la Ampe (A), dan vi dien tfch q la Culong (C)

Ngoai ra trong thuc te con dung:

Kilo Ampe: lkA = 10? A

Mili Ampe: 1mA = 10'3 A

Micro Ampe: 1 fj A = 10‘r,A

2.2 Vecta m at do dong dien

Cuong do dong dien chi dac trung cho do manh yeu cua dong dien qua mot dien tfch nao do, chua dac trung cho do manh yeu cua dong dien tai tung diem trong moi truang ngoai ra cuang do dong dien con chua cho ta biet phuang, chieu cac dong dien Vi vay, ngoai cudng do dong dien, ngudi ta con dung mot dai lupng vat ly khac de dac trung cho dong dien do la vecta mat do dong dien

2.2.1 Dinh nghia

Vecto’ mat do ddng dien j tai mot diem M trong moi trudng co ddng dien la mot vecto cd goc tai M, cd phuong chieu la phuong chieu ciia dien tich duong chuyen ddng qua diem dd, cd do ldn bang

cudng do ddng dien qua mdt don vi dien tich

dat vuong goc vdi phuong chuyen dong dy.

De tfnh cuang do dong dien qua dien tich

S bat ky, ta phai chia dien tfch S do thanh

nhung phan tir dS, sao cho tren dS, j khong doi

Goi dSn la hinh chieu dS tren phuang vuong goc

vai j ; thi ro rang cuang do dong dien qua dSn

cung bang cucmg do qua dS

Trong he SI dan vi cua j la: A/m2

2.2.2 Su lien he giua vecta mat do ddng dien vd vecta van toe cua cac

dien tich chuyen dong

Neu goi n0 la mat do dien tich tu do |qj la

do lan m6i hat dien tfch, v la do lan van toe

m6i hat thi j, n0, |q |, v co moi lien he vdi nhau

Thuc vay trong mot dan vi thdi gian sd hat

dn = n„ v.dS„

110

Do do cudng do dl qua dSn se la:

TU TRUdNG DONG DIEN KHONG DOI■

Chuong 3

1 Thi nghiem ve titong ta c tuT cua dong dien

Ta da biet xung quanh mot nam cham xuat hien mot tir trucmg Nho tir truang ma cac nam cham tuang tac duac vai nhau (cac cue cung dau day nhau, khac dau hut nhau) Tuang tac cua nam cham vai nhau goi la tucmg tac tir

Cac thi nghiem sau day chung to dong dien cung co tir tfnh nhu nam cham, nghla la xung quanh dong dien cung xuat hien mot tir trudng

N

N

1.1 Thi nghiem 1

Dat mot kim nam

cham tu do thi kim nam

cham luon luon chi theo

huong Bdc Nam Cang mot

sai day ddn sao cho phuang cua soi day song song vai true ciia nam cham (hinh 3.1a) Neu cho dong dien khong ddi di qua sai day thi kim nam cham bi quay di

1 goc (hinh 3.1b)

(a)

Hinh 3.1 (to

1.2 Thi nghiem 2

Dua nam cham thing vao gan mot ong

day ddn cd ddng dien chay thi thay nam cham

cd the hut hoac day ong day dd (hinh 3.2)

1.3 Thi nghiem 3

Cd hai day ddn dat song song vdi nhau

Neu cho ddng dien chay qua hai day ddn dd

cung chieu thi thay hai day ddn dd hut nhau

neu ddng dien chav nguoc chieu thi hai day ddn

dd day nhau (hinh 3.3)

1.4 Ket luan

Qua nhieu thf nghiem chting to nam cham tac dung len nam cham cung giong nhu dong dien tac dung len nam cham, hay nam cham tac dung len dong dien hoac dong dien tac dung len dong dien

Vay xung quanh nam cham va xung quanh day ddn co dong dien chay qua deu xuat hien mot tti trudng Tuong tac giua nam cham voi nam cham, dong dien voi dong dien, hay giua nam cham vdi ddng dien d6u cd cung ban chat duoc goi la tuong tac tti

2 Djnh lu at A m pe (Amper) ve ttfdng tac ttt cua dong dien

2.1 Phan tu dong dien

Tren mot day ddn cd ddng dien I ch

mot doan nhd MN, MN coi la thing, thi

MN duoc dinh nghla la: I.d l, trong dd d

MN, cd chieu la chieu ddng dien I cl

(hinh 3.4)

2.2 Dinh luat Ampe

2.2.1 Trong chan khong

Gia su trong chan khdng cd 2 ddng

dien I, I() Tren day ddn cd cudng do I, tai

O ta lay phan tu ddng dien I.dl, tren day

ddn cd cudng do I() ta lay phdn tti ddng

dien I() dl0 tai dieim M Ke vecto r = OM

Dung mat phdng P chtia I dl va r

Tai M ke phap tuyen n vdi mat phdng P

sao cho thti tu 3 vecto I d l, r , n lap thanh

mot tam dien thuan

Goi 0 la goc giua I dl va r, 0ola goc giua I0.dl0 va n (hinh 3.5)

Qua thuc'nghiem chting to luc tac dung cua phan tu I dl len phan tir I() di^ la mot luc dF0

- Cd phuong vuong goc vdi phan tir I() dl0 va vuong goc vdi n

- Cd chi£u sao cho thti tu ba vecto I() dl0 , n va dF^ lap thanh tam dien thuan

lay qua neu ta thay phan tir ddng dien

1 la vecto cd do dai lay trong day ddn

Hinh 3.5

- Co do ldn:

I.dl.sin.0.1o.dlo.sin0odF()= K

2.2.2 Trong cac moi trudng

Thuc nghiem cung chting to, hai phan tti dong dien neu dat trong moi trudng, cung khoang cach so vdi khi dat chung trong chan khdng thi lire tac dung

se thay doi lan

d F = l i dFg.

(j dupe goi la do tti tham cua mdi trudng

Neu (i> 1 thi mdi trudng dd goi la chat thuan tti n < l thi duoc goi la mdi trudng nghich tti

Va dinh luat Ampe dupe viet tong quat cho cac mdi trudng la:

^ = (I0 d l j A ( I d I A f )

Nhan xet: Dinh luat Ampe la dinh luat co ban cua tuong tac tti That vay,

ddng dien chfnh la tap hop cua cac phan tti ddng dien, do dd neu biet tuong tac giua hai phan tti ddng dien ta cd the tfnh dupe tuong tac gitia cac ddng dien cung giong nhu dinh luat Culong la dinh luat co ban cua tuong tac dien tfch

3 Vecto cam ting tuf, vecto ctfbng do tit trifbng

3.1 Vecto cam ung tir B

Tu dinh luat Ampe, neu ta xet vecto

114

thi vecta dB chi phu thuoc vao I dl la ph&n tu dong dien gay ra tir trudng va vi trfcac diem xet, khong phu thuoc vao I0 dl0 dB duac goi la vecta cam ting tti dophdn tti dong dien I dl gay ra tai diem M.

Bieu thtic (3) duac goi la dinh luat Bio-Sava-Laplat

Dinh ly duac phat bieu nhu sau: Vecta cam itng tilt do phan tit ddng dien gay

ra tai mot diem trong tit trudng co:

- Phuang vuong goc vdi mat phdng chita phan tit ddng dien vd diem xet (mat phdng chita I d l , r ).

- Chieu sao cho thit tit ba vecta I d l , r , dB lap thanh tam dien thuan (chieu ciia r ).

- Chieu cua vecta dB con cd the tim theo quy tac cai dinh dc sau day:

Dat cai dinh o'c theo phuang ciia ddng dien vd van dinh dc sao cho no tien theo chieu ddng dien, thi chieu quay ciia cai dinh dc la chieu ciia vecta d B

- Trong he SI, dan vi cam ting tti la Tesla (T)

3.2 Nguyen ly chong chat tir trudng

Dua vao dinh luat Ampe, ta cd the tfnh duac vecta cam ting tir cua ca ddngdien hoac n ddng dien gay ra tai mot diem trong tir trudng That vay:

- Ddi vdi mot ddng dien:

Bieu thtic (5) va (6) goi la nguyen ly chong chat cua tti truong.

trong do, B, la vecto cam ting tijr do dong dien thu i gay ra.

3.3 Vecto cudng do tti trucmg H

Cung giong nhu dien truong, ngoai vecto E , ngudi ta con dung vecto D de dac trung cho dien truong Trong tti trudng ngoai vecto B ta con dung mot dai lupng vecto cudng do tti trudng H dupe dinh nghla:

Dua vao dinh luat Ampe va nguyen ly chong chat ciia

tti trudng, ta cd the tfnh dupe vecto cam ting tti B cho cac

ddng dien Ta chi xet mot sd trudng hop dac biet sau:

3.4.1 Ddng dien trdn

Gia sir cd mot day dan hinh trdn ban kfnh R, cd

ddng dien I chay qua Ta hay tfnh cam ting tti do ddng

dien gay tai tam O

Xet phan tti I dl bat ky, ta thay:

I la cuong do dong dien

S la mot vecta co cuang do lan bang dien tfch ciia hinh tron chua vong day

co dong dien chay, chieu cua S la chieu cua B tai do:

Neu dung khai niem:

Pm=I-Sthi cam ung tu: B do dong dien tron gay ra tai tam O co the viet

0 2.7T.R3 2ti.R3

- De tim chieu cua vecto cam ling tir gay ra doi vai dong dien tron, nguai ta con dung quy tac kim dong ho nhu sau:

Nhin vao vong day, neu dong dien chay

nguoc chieu kim dong ho thi do la cuc bac

(duong sue cam ung tu di ra tu cuc bac) neu

dong dien chay cung chieu kim dong ho do la

cuc nam

Biet B0 ta co the tfnh H0:

H q= B 0 _ I S _ Pm (i 2.71.R’ 271 R'

Ve do lan:

H ° 2R

Hinh 3.7

Ro rang theo (9) trong he SI don vi cua H se la

(A/m).'

3.4.2 Ddng dien thdng

Gia su co day dien thing dai AB, co cuong do

I di qua Hay tmh cam ung tir B va H do dong

dien gay ra tai mot diem M cach day ddn mot

khoang R (hinh 3.8)

Muon vay tren day ddn tai mot diem C bat ky

ta lay mot phan tu dong dien I dl thi I dl se gay ra

tai M mot vecto cam ting tir co phuong, chieu xac dinh bang quy tac cai dinh 6c (trong hinh ve co phuong vuong goc voi mat phang chua I.dl va diem xet chieu

d(cotg 0) =

R.d0

d0sin:0

R sin 6

c a m On g d ie n■ tui

Chuong 4

1 Thi nghiem ve hien ttfong cam ting dien tti

Ta da biet dong dien gay ra xung quanh no mot tur trucmg

Vay nguoc lai tir truang co the gay ra dong dien khong?

Nam 1831 nha vat ly hoc ngudi Anh Faraday bang thuc

nghiem da chting to khi cd tu trudng bien doi da sinh ra trong

mach km ddng dien, goi la ddng dien cam ting, hien tuang dd

goi la hien tuang cam ting dien tur

Phat minh ra hien tuong cam ting dien tir la mot trong

nhung phat minh quan trong nhat cua vat ly ndi rieng va

khoa hoc ndi chung

»

1.1 Thi nghiem 1

Dung mot nam cham thing de gan dau mot ong day A

ong day A duac ndi vdi dien ke nhan G (hinh 4.1)

- Neu giu nguyen ong day va dich chuyen nam cham

thi trong thdi gian nam cham dich chuyeh, trong ong day A

cd ddng dien Do ldn, chieu cua ddng dien phu thuoc vao toe

do dich chuyen cua nam cham (neu dich chuyen thanh nam

cham cang nhanh thi cudng do ddng cam ting cang ldn Neu

dua cuc bac lai gan ong day, thi ddng cam ting xuat hien cd

chieu nguoc chieu vdi khi dua cuc bac ra xa ong day)

- Neu giu nguyen nam cham va dich chuyen ong day thi

hien tuang cung xay ra tuang tu nhu tren Vay khi cd sir

chuyen dong tuang ddi giua nam cham va ong day thi trong

ong day xuat hien ddng cam ting

- Neu dong khoa K Cho 2 ong day A, B chuyen dong tuong doi thi ong day

A cung co dong cam ting nhu thf nghiem 1

- Neu de A va B dting yen, dong hoac ngat khoa K ta cung thay trong ong day A xuat hien dong cam ting Dong cam ting co chieu khi dong K nguoc chieu voi dong cam ting xuat hien khi ngat khoa K

* Nhan xet: Qua thf nghiem 2 ta thay mot ong day co dong dien mot chieu

chay qua tuong duong vdi mot nam cham thing, ta goi la nam cham dien

* Ket litan: Qua nhieu thf nghiem, Faraday da di den ket luan.

- Khi tu thong qua mach kin bien doi thi trong mach kin xuat hien dong cam ting

- Dong dien cam ting chi ton tai trong thoi gian tir thong bien doi qua mach km

- Cudng do dong dien cam ting ty le thuan vdi toe do bien thien tir thdng qua mach kin

- Chieu cua ddng dien cam ting phu thuoc vao su bien doi cua tir thdng qua mach kin dd tang hay giam

2 Cac djnh lu a t cd ban ve cam ting dien tt i

2.1 Djnh luat Lenxa ve chieu dong cam ung

2.1.1 Phat bieu

Ddng cam ting bao gid cung co chieu sao cho tit tntdng do no sinh ra chong lai nguyen nhan sinh ra no.

2.1.2 Thi du

Trong thf nghiem dua cuc bac cua nam cham lai

gan dau cua ong day A, ta thay tir thdng qua ong day A

tang len, theo dinh luat Lenxo ddng cam ting phai cd

chieu sao cho tir trudng do no sinh ra chong lai su tang

tir thdng dd Muon vay dudng sue tir trudng do ddng

dien trong ong day gay ra phai nguoc chieu vdi dudng " v ^

stic tir do nam cham gay ra (hinh 4.3)

Hinh 4.3

Ap dung quy tac kim ddng hd, ta thay dau ong day A d gan nam cham phai

la cuc b k Tuong tu neu dua cuc bac nam cham ra xa ong day thi dau ong day A

d gan nam cham se phai la cuc nam Ddng dien trong ong day luc dd se chay theo chieu nguoc lai Chti y: muon dich chuyen nam cham ta phai ton nang luong co hoc, nang luong nay da bien thanh nang luong ddng cam ting, vay dinh luat Lenxo la bieu hien cua dinh luat bao toan nang luong

Sir xuat hien dong dien cam ung chung to trong mach xuat hien mot sua't dien dong Suat dien dong do goi la suat dien dong cam ung.

De tfnh suat dien dong cam ung, ta xet mot thf nghiem tong quat nhu sau:Dich chuyen mot vong day km (C) trong tu truong tir vi trf (1) den vi trf (2) sao cho tir thong qua mach kin do bien doi (hinh 4.4)

Gia sir sau thoi gian dt, tu- thong qua mach km bien doi mot luong d < f> m va

cudng do dong cam ting la Ic Khi do cong tir luc tac dung len dong cam ting

se la:

dA=Ic d OmTheo dinh luat Lenxo, tir luc tac dung len dong dien cam ting phai ngan can sir dich chuyen cua vong day vi su dich chuyen nay la nguyen nhan gay ra dong cam ting nen cong cua tir luc tac dung len dong cam

ting phai la cong can

Vi the de dich chuyen vong day ta phai ton mot

cong dA' bang cong can do

dA' = - dA = -Ic d<DmTheo dinh luat bao toan nang luong, cong dA'

phai dupe chuyen thanh nang lupng cua dong dien

cam ting Neu goi ec la suat dien dong cam ting, ta

phai co:

ec.Ic.dt Ic d®m

2.2 Djnh luat Faraday ve suat dien dong cam urng

(1) dupe goi la dinh luat Faraday ve sua't dien dong cam

ting, phat bieu nhu sau:

Suat dien ddng cam Ung luon luon bang ve tri sd nhung

trai ddn vdi toe do bien thien tti thdng giri qua dien tich ciia

mach dien

C hi y: Theo dinh luat Lenxo cong cua tir luc tac dung

dong cam ting bao gift cung la cong can do do dd djch

chuyen mach dien trong tir trudng ta phai ton mot cdng bang

ve tri so nhung trai dau vdi cdng can dd Vi vay, dau (-) trong

bieu thtic (1) chfnh la bieu hien ve mat toan hoc cua dinh luat Lenxo

Hinh 4.4

( 1)

Hinh 4.5

122

Vay dinh luat Faraday ve suat dien dong cam ung chinh la dinh luat tong quat cua hien tuong cam ung dien tit.

3 M o t so trUdng hop dac biet cua cam ting dien tti

3.1 Dong dien xoay chieu

Mot trong cac ung dung quan trong cua cam ung dien tir la tao ra dong dien xoay chieu Dong xoay chieu la tru'dng hop dong cam ung xuat hien khi co bien thien tu thong tuan hoan qua mach km

That vay, ta hay xet mot khung day dat trong mot tu truong deu cam ung

tu B C) thdi diem t = 0, B vuong goc vdi mat phlng cua khung, tu thdng qua mach la:

- Neu khung day gom nhieu vong day nhu nhau thi:

e0= N 0 0.co = N.B.S.co

3.2 Dong dien Phuco

Khi cd mot khoi vat ddn chuyen dong trong tic trucmg, hoac dien trucmg bien thien trong khoi vat ddn thi trong khoi vat ddn do cimg xuat liien mot ddng dien cam i(ng, trudng hop nay goi la ddng Phuco

Cudng do cua dong Phuco la:

eF

lp “R

Vi R rat nho nen iF rat Ion, theo djnh luat Jun - Lenxo thi tac dung nhiet cua dong Phuco rat Ion Vdi dac diem dd ddng Phuco cd vai trd quan trong trong ky thuat

3.2.1 Tac hai cua ddng Phuco

Trong cac bien the dien, may phat dien, dong co dien loi sat cua chung se xuat hien cac ddng Phuco, mot phan nang lupng se mat di dudi dang toa nhiet, dac biet neu cac loi sat dd cd dien trd rat nhd thi tac dung nhiet rat ldn, cd the bj nong chay

De lam giam tac dung nhiet nay, cac loi ngudi ta khdng dung ca khoi kim loai ma gom nhidu la kim loai mong ghep lai, cac la kim loai nay dupe son cach dien vdi nhau

124

DAO DONG DIEN TO - SONG DIEN TO■ ■ ■

1 Cac luan diem cua Macxoen

1.1 Luan diem Macxoen thti nhat

Nhu chting ta da biet, thf nghiem cua Faraday ve hien tupng cam ting dien tur

da chting to khi ta lam bien doi tti thong gui qua mot vong day khep km, bang cach dat vong day ay trong mot tti truang bien thien, trong vong day ay xuat hien mot dong dien cam

ting co chieu xac dinh

boi dinh luat Lenxo:

neu tu thong gtii qua

vong day tang, dong

dien cam ting co chieu

nhu tren hinh 5.1; neu

tti thong gtii qua vong

day giam, dong dien

cam ting co chieu nhu

la, vong day khong phai la nguyen nhan sinh ra dien truang, ma chi la phuang tien giup ta phat hien su co mat cua dien truong do Trong hien tupng cam ting dien tir, nguyen nhan gay ra dong dien cam ting la sir bien doi cua tti thong gtii qua mach dien, ttic su bien doi cua tir trudng tai noi dat mach Vay dien trudng gay nen ddng cam ung chi cd the do tti trudng bien ddi theo thdi gian sinh ra

Ro rang dien trudng nay khdng the la dien trudng tinh vi dudng stic cua dien trudng tmh la dudng cong hd, cdng cua dien trudng tinh trong su dich chuyen hat dien theo dudng cong km bang 0

VI vay, dien truang tinh khong the lam cho cac hat dien dich chuydn theo duang cong km de tao thanh dong dien duac (Vi neu dien truang tinh tao nen duac dong dien khep km thi nghla la ta co the khong ton cong ma van sinh ra duoc nang luong dien?) Muon lam cho cac hat dien chuyen dong theo duang cong km thi cong cua dien truang trong su dich chuyen hat dien theo duang cong kin phai khac khong:

Jq.E.dio

Nghia la cac duang sue dien trudng phai la cac dudng cong km Thuc nghiem da xac nhan rang, dien trudng gay nen ddng dien cam ung cd nhung dudng sire khep km Vi vay, ngudi ta goi dien trudng nay la dien trudng xoay.Tom lai, tren ca sd phan tfch nhu tren, Macxoen da phat bieu duac mot luan diem tong quat, goi la luan diem thu nhat cua Macxoen:

Bat ki mot tif trudng nao bien doi theo thdi gian cung sinh ra mot dien trudng xoay.

1.2 Luan diem thu hai cua Macxoen

Theo luan diem thu nhat cua Macxoen, tir trudng bien doi theo thdi gian sinh ra dien trudng xoay Vay nguoc lai dien trudng bien doi theo thdi gian cd the sinh ra tir trudng khdng? De dam bao tmh ddi xung trong mdi lien he giua dien trudng va tir trudng, Macxoen da giai quyet van de nay bang mot luan diem goi la luan diem thu hai cua Macxoen:

Bat ki mot dien trudng nao bien doi theo thdi gian cung sinh ra mot tif trudng.

Luan diem nay da duac thuc nghiem chung minh

Nhu vay, neu theo luan diem thu nhat, tir trudng cd the sinh ra dien trudng thi vdi luan diem thir hai, Macxoen da khang dinh rang, nguac lai, dien trudng cd the sinh ra tir trudng O day, can luu y la dien trudng ndi chung cd the khdng ddng deu trong khdng gian, nghla la no cd the bien doi tu diem nay sang diem khac, nhung theo luan die’m thu hai cua Macxoen, su bien doi nay ciia dien trudng khdng sinh ra tir trudng ma chi cd su bien doi cua no theo thdi gian mdi sinh ra tir trudng

2 Sir tao th an h song dien tuT Cac tfnh cha't, dac diem cua song dien tuf

2.1 Su tao thanh song dien tir

Hec da lam thi nghiem sau:

126

AB the nao do de co hien tupng phong dien giua AB Nhu vay giua AB da xuat hien mot dien trudng bien thien theo thdi gian Neu dung cac dung cu phat hien,

ta se thay tai moi diem M trong khdng gian d£u cd cap vecto cudng do dien trudng E va cudng do tu trudng H , chung cung bien thien theo thdi gian Vay thf nghiem Hec chung to: dien tur trudng bien thien da dupe truyen di trong khdng gian Qua trinh dd dupe giai thfch nhd hai luan di£m cua Macxoen

Thf du: Tai mot diem O, ta tao ra mot dien trudng bien thien: vecto cudng do dien trudng E bien thien theo thdi gian Theo luan diem thu hai cua Macxoen, dien trudng d O bien thien se tao ra tu trudng, nghla la tai cac diem M, M \ M ” xuat hien cac vecto cudng do tu trudng H , H ', H " vi E bien thien tuan hoan theo thdi gian nen H , H ', H " cung bien thien tuan hoan theo thdi gian Theo luan diem thu nhat cua Macxoen, tu trudng bien thien gay ra dien trudng xoay, tai cac diem M \ M ” xuat hien cac vecto cudng do dien trudng E ', E" Nhu vay,

ta thay cap vecto E , H da dupe truyen den moi diem trong khdng gian, qua trinh truyen dd goi la song dien tir

Song dien tif la tntdng dien tif bien thien truyen di trong khdng gian.

2.2 Cac tm h chat, dac diem cua song dien tir

+ Song dien tu ton tai ca trong mdi trudng vat chat va trong chan khdng (khac vdi song co hoc khdng ton tai trong chan khdng)

+ Song dien tu la song ngang: tai mdi di£m trong khdng gian cd song dien

tu, phuong cua cac vec to E , H , tuc la phuong dao dong, deu vuong goc vdi phuong truyen song

+ Van toe truyen song dien tu trong mot mdi trudng ddng nhat va ding hudng:

v = —j= e : Hang sd dien mdi, (i: dd tu tham cua mdi trudng.

n = Je\± : chiet suat tuyet doi cua moi trudng.

Trong chan khong e = 1, n = l, vay v = c = 3.108 m/s

Thuc nghiem chung to n> 1, do do c>v, nghla la van toe truyen song dien tir trong chan khong la Ion nhat so voi cac moi truang khac

3 Thang song dien tuf

Nguai ta goi song dien tir phang dan sac la song dien tir co tan so (hoac buoc

song xac dinh) Goi k la buac song, T la chu ki, v la van toe truyen song dien tir

trong moi truang ta co:

k = v.T

Vi v = — nen X = — = —

Trong do k0= c.T la buac song cua song dien tir trong chan khong Vay buac

song cua song dien tir phu thuoc moi trudng, cd gia tri ldn nhat trong chan khdng.Ngudi ta phan loai cac song dien tir dan sac theo do ldn tan sd (tinh ra dan vi Hec) hay budc song (trong chan khdng) Ta cd the lap mot bang trong dd ghi ten cac loai song dien tir ung vdi nhung budc song tir nhd den ldn goi la thang song dien tir

Song vo tuyen dien

X (cm)

- 102

10 °

10Song hong ngoai

Quang ph6 thay duac

Song tir ngoai

Thang song dien tir

128

P h a n th ti tu

QUANG HOC

Quang hoc la mon hoc nghien cuu ve anh sang.

Trong phan nay chung ta se nghien cuu cac hien tuong quang hoc nham hieu

ro ban chat cita dnli sang, dong thdi se cung cap nhung kien thuc can thiet ve viec ung dung nhung dinh luat quang hoc trong ky thuat vd ddi song.

129

CO sd CUA QUANG HINH HOC-DUNG CU QUANG HOC■ ■ ■ ■

Chuong 1

1 Cac djnh lu a t cd ban cua quang hinh 119c

Quang hinh hoc dua tren bon dinh luat co ban sau day:

1.1 Djnh luat ve su truyen thing cua anh sang

Dinh luat duac phat bieu

Trong mot moi trudng trong suot, dong tinh vd ddng huong, anh sang truyen theo dudng thdng.

Khi nghien cuu hien tupng nhi£u xa, ta se thay dinh luat nay co gidi han ung dung cua no Khi anh sang truyen qua nhung Id that nhd hoac gap nhung chudng ngai vat kfch thudc nhd vao cd budc song anh sang thi dinh luat tren khdng con dung nua

1.2 Dinh luat ve tac dung doc lap cua cac tia sang

Dinh luat dupe phat bieu:

Tac dung ciia cac chiim sang khac nhau thi doc lap vdi nhau Nghia la, tac dung ciia mot chiim sang nay khong phu thuoc vao su cd mat hay khdng ciia cac chum sang khac.

1.3 Hai dinh luat cua Decac (Descartes)

Thirc nghiem xac nhan ring, khi tia sang 01 tdi mat phan cach hai mdi trudng trong suot ddng tfnh va ding hudng thi tia sang bi tach thanh hai tia: tia phan xa IR, va tia khuc xa IR2 (hinh 18.1)

Chung tuan theo hai dinh luat sau day:

1.3.1 Dinh luat Decac thit nhdt - dinh luat phan xa

Tia phan xa nim trong mat phing tdi (tuc la mat phing chua tia tdi va phap tuyen IN) va goc tdi bing goc phan xa

131

1.3.2 Dinh luat Decac thu: hai - dinh

luat khuc xa

Tia khuc xa nam trong mat phang tai va

ty so giua sin goc toi va sin goc khuc xa la mot

so khong doi

sini,

n2_, la mot so khong doi, phu thuoc vao ban

chat cua hai moi truong, duoc goi la chiet suat

ti doi ciia moi truang 2 doi v6i moi truang 1 Hinh 1.1

Neu n21 > 1 thi i2<i,, tia khuc xa gap phap tuyen va moi truang 2 duac goi la chiet quang han moi truang 1 Nguac lai, neu n,.,<l thi i2>i,, tia khuc xa lech xa phap tuyen han va moi truong 2 kem chiet quang han moi truang 1

1.3.3 Chiet suat ti doi vd chiet suat tuyet ddi

Neu goi v, va v2 la van toe anh sang trong moi truang 1 va 2, tu thuc nghiem chung to:

Doi vai khong khi v * c nen n ~ 1

Ta tim moi lien he giua chiet suat ti doi cua hai moi truang va chiet suat tuyet doi cua chung Tu (3) co the viet:

n2-,= V, _ C e _ n2

Neu moi truang thu nhat la khong khf thi n, ~ 1 va n,., ~n2 Do do co the coichiet suat tuyet doi cua mot moi truong la chiet suat ti doi cua moi truang do doi voi khong khi

1.3.4 Dang ddi xitng cua dinh luat Decac

Tir (2) va (5) co the viet:

sini

sini,

2-1 = ^n,Hay:

(6)

n^sini, = n2.smi2Bieu thCrc (6) la dang doi xurng cua dinh luat Decac

1.4 Hien tuong phan xa toan phan

Hai dieu kien de hien tupng phan xa toan phan xay ra:

- Thu: nhat la anh

sang phai di tu moi

truong chiet quang

manh sang moi truong

chiet quang kem hon,

thf du di tu nude ra

khong khf Khi do ta co:

n, sini | = n2.sini2

i, < i2 , turc la goc toi nho

hon goc khuc xa Khi tang goc tdi thi goc khuc xa cung tang, nhung luon luon co ii<i2 Khi goc khuc xa i2 = 90° thi goc toi den mot gia tri goi la goc tdi toi han (ig)

- Thu' hai la goc toi phai ldn hon (hay toi thieu la bang) goc tdi toi han, tuc la:

Khi do thi toan bo tia sang di toi mat phan cach hai moi truong se phan xa trd lai mdi trudng thur nhat Hien tupng nay goi la phan xa toan phan Luc dd, ta cd:

n l s i n i (?= n , s i n 9 0 °

/ n \ / n \

(7)

* Ung dung cua hien tuong phan xa vd khuc xa anh sang

- Dua vao hien tupng khuc xa va phan xa toan phan cd the giai thfch duac hien tupng cac ao anh quan sat dupe d cac vung sa mac hay dong cd (hinh 1.3) Nhd su uon cong cua tia sang nen mot sd vat d khuat xa dudi dudng chan trdi se dupe nhin tha'y va hinh nhu d gan ngudi quan sat han

n 2 • -1 n 2

i = arcsin & = sin

v n i , v n i ,

- Dua vao tfnh chat khi guang

phang quay mot goc a thi tia phan

xa quay mot goc 2 a , ngudi ta gan

mot guong phang vao khung treo

cua mot dien ke Khi co dong dien

mot chieu chay trong khung day,

khung day se quay keo theo ca

guong cung quay Chieu mot chum

tia sang vao guong, khi guong quay thi tia sang phan xa se quay mot goc Ion gap doi, tire ia da tang do nhay cua dien ke Do la nguyen tac ca'u tao cua dien

ke guong

- Hien tupng phan xa toan phan dupe ung dung de doi chieu tia sang trong cac dung cu quang hoc Chiet suat cua thuy tinh vao co 1,5 Vi vay, goc toi tdi han tren bien gidi thuy tinh - khdng khf cd ig » 42°, khi goc tdi bang 45 ' se luonluon xay ra hien tupng phan xa toan phan Hinh 1.4 bieu di£n cac lang kfnh phan

Lang kfnh phan xa toan phan dupe ung dung

nhieu trong cac dung cu quang hoc nhu kfnh ti6m

vong, kfnh hien vi khuc xa ke Ngay nay hien tupng

phan xa toan phan con dupe ung dung trong cap spi

quang (O.F = Optical Fibers) Spi quang hoc cau tao

gom hai ldp (xem hinh 1.5), loi cd chiet suat n,, vd

cd chiet suat n2, vdi di£u kien n,>n2 Khi cho anh

sang (tia laser) di vao mot dau spi quang (phan loi),

anh sang se phan xa toan phan nhieu lan trong loi ma khdng bi lot ra ldp vd nhu

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