• Khi mdt khdng dieu tie't, diem tren true cua mdt md dnh dugc tao ra ngay tai mang ludi ggi la die'm cite viSn C^, (hay vien diem) eua mdt. Dd ciing la diem xa nhdt ma mdt ed thd nhin rd. Ddi vdi mdt khdng cd tat, didm circ vidn d xa vd cung (vd cue).
• Khi mdt dieu tiet tdi da, didm trdn true ciia mdt ma dnh cdn dugc tao ra d ngay tai mang ludi ggi la diem cue can C^ (hay can diem) cua mdt. Dd cung la didm gan nha't ma mdt cdn nhin rd. Cang Idn tudi, diem cue can cang lui ra xa mdt (xem Bang 31.1).
• Khodng cdch giua did'in cue vidn va didm cue can ggi la khodng nhin rd cua mdt. Cac khoang each OC^ va D = OC^ til mdt tdi cac didin cue vidn va cue can ciing thudng dugc ggi tuong iing la khodng cifc vien. khodng cite can.
Ill - N A N G S U A T P H A N LI CUA MAT
Mudn eho mdt nhin tha'y mdt vat thi anh that eua vat tao bdi mdt phdi hien ra d mdng ludi, nghia la vat phdi cd vi trf d trong khoang nhin rd eiia mdt. Tuy nhien, trong nhidu trudng hgp cdn cd nhu cdu la quan sat dugc cdc chi tiet nhd eua vat, ehdng han dgc dugc chu ctia mdt trang saeh bdo hoae nhan ra ngudi quen trong mdt tdm dnh nhd chiip nhidu ngudi,...
Vide nhin thdy dugc mdt vat nhd AB chdng han, tuy thude vao kich thude dnh A'B eiia vat dd trdn mdng ludi. Kfch thude ndy phu thude gdc trdng vat (Hinh 31.4). K l
Dd mdt ed the phan biet duge hai diem AvaB thi goc trdng vat khdng the nhd hon mdt gid tri tdi thieu ggi la ndng sudt phdn li e cua mdt.
Khi dd, dnh cua diem ddu va diem cudi cua vat dirge tao ra d hai te bdo thdn kinh thi giac ke can nhau. Nang sudt phan li thay ddi tuy theo timg ngudi, nhung gid tri trung binh Id :
e= a V
Hinh 31.4 Gdc trong vat
m Gdc trdng mot vat la gi va phu thuoc vao cac yeu td nao ?
IV - CAC TAT CUA M A T V A C A C H K H A C PHUC Ta chi xet cac tat phd bien nha't Id : mat can. mdt vien vd mdt lao.
1. Mat can va each khac phuc
a) Mdt can cd do tu lon hon do tu ciia mdt binh thudng. Mdt chum tia sdng song song truydn den mdt can se eho chum tia Id hdi tu tai mdt diem d trude mdng ludi (ffinh 31.5).
Hinh 31.5 Sa dd minh hoa dac diem quang hoc ciia mat can
Cae he qua :
, Khodng each OC^ huu han.
. Diem C gdn mdt hon binh thudng.
Tat can thi cd the do bdm sinh, nhung ciing cd thd do dgc sdch hay hge bdi d ehd khdng du do sang hoae dat saeh qud gdn mdt mdt thdi gian ddi.
Hmh 31.6
Sd do minh hoa each khic phiic tat can thi
b) Tat can thi thudng dugc khde phuc bdng each deo kfnh phan ki cd do tu thfeh hgp dd cd the nhin rd vat d vd cue ma mdt khdng phai didu tie't (ffiinh31.6). U^
Ndu coi nhu kfnh deo sat mdt thi tidu eu cua kfnh duge xde dinh bdi :
f=-oc^
P F Hay chdng to rang, he ghep (mat can + thau kinh phan kl) cd dd tu nho hon dd tu cCia mat can.
2. M a t v i e n va each khac phuc
a) Mdt vidn cd do tu nhd hon do tu cua mdt binh thudng. Mdt chum tia sang song song truyen den mdt vidn se cho chum tia Id hdi tu tai mdt diem sau mang ludi (ffiinh 31.7).
Hinh 31.7
So do minh hoa dac diem quang hoc cua mSt vidn
Cae he qua :
, Mat vidn nhin vat d vd cue da phai dieu tie't.
, Didm C^ xa mdt hon binh thudng.
b) Ngudi vidn thi didu tiet mdt (giam tieu eu) ed the nhin thdy dugc eae vat d xa. Tat vidn thi thudng dugc khde phuc bdng each deo kfnh hdi tu dd cd the nhin rd eae vat d gdn mdt nhu mdt binh thudng. Tidu cu eiia thdu kfnh phdi ed gia tri thfeh hgp de dnh do eua diem gdn nha't ma ngudi vidn thi mudn quan sat duge tao ra tai didm cue cdn eua mdt.
3. M a t lao va each khac phuc
a) Vdi hdu hd't mgi ngudi, ke tii tudi trung nien, kha nang dieu tiet gidm vi eo mdt ydu di va the thuy tinh trd nen eung hon. Hau qua la diem cue can C ddi xa mdt. Dd la tdt lao thi (mdt lao). Khdng ndn coi mdt lao la mat vidn. Mdt khdng tat, mdt can hay mdt vidn khi Idn tudi ddu cd them tat lao thi.
b) De khde phuc tat lao thi, phdi deo kfnh hdi tu tuong tiJ nhu ngudi vidn thi.
Dac biet, ngudi cd mdt can khi Idn tudi thudng phdi:
. deo kfnh phan ki de nhin xa.
. deo kfnh hdi tu de nhin gdn.
Ngudi ta thudng thire hien loai ''kinh hai trdng' ed phdn tren phan ki vd phdn dudi hdi tu.
Bdi tap vi du 2
Mot nguai can thi lon tu6i ehi con nhin tha'y r5 eae vat trong khoang each mat 50 em ^ 67 em.
Tinh dp tu ciia cac kinh phai deo d6 nguoi nay co th6 : - nhin xa vo ciing khong dieu tie't.
- doc duoc saeh khi dat gin mdt nha't. each mat 25 cm.
Coi kinh deo sat mdt.
Gidi
- De nhin xa phai eo (ITmh 31.8) :
/ l = D, =
-O^Cy = - 6 7 cm ==: - -
— = -1,5 dp
- De doc saeh dat gan mat nha't, kinh CO tieu c u / , xac dinh bdi :
1 25 D,=
— = — => A = 50 cm 1 1 50 / . ^'-
— = 2 d p 1 h
m
each mat
= 0,50 m
25 cm phai deo
V - HIEN TU'gfNG LU'U ANH CUA M A T
Nam 1829, Pla-td (Plateau) - nha vat If ngudi Bi phdt hien ra la cam nhan do tde ddng ciia dnh sdng len cdc te' bdo mang ludi tiep tue tdn tai khoang —- giay ddng hd sau khi chiim sdng tdt. Trong thdi gian
— giay nay ta vdn edn '"thdy" vat, mac du dnh eua vat khdng cdn duge tao ra d mdng ludi niia.
Dd la hien tugng luu dnh ciia mdt. Nhd hien tugng ndy ma mdt nhin thdy ede anh tren man dnh chieu phim (ffiinh 31.9), trdn mdn hinh tivi (ffiinh 31.10),... ehuyen ddng.
(~) Y
'-'""
Cv! - ---^.^A ( 0 ^ " " ^
' A ~^
l^1l
Hmh 31.8
Hmh 31.9
Hinh 31.10
Cau tao cua mat gom : mang giac, thuy djch, long den va con ngUori, the thuy tinh, dich thuy tinh, mang ludi.
Dieu tiet la sir thay doi tieu cU cua mat de tao anh cua vat luon hien ra tai mang lUdi.
+ Khong dieu t i e t : f^^^
+ Dieu tiet toi da : f-„
mm
- Diem cUc vien la diem tren true ciia mat ma mat nhin ro khi khong dieu tiet.
Mat khong tat thi C^ or vo cUc.
- Oiem cUc can la diem tren true cua m j t ma mat nhin ro khi dieu tiet toi da.
Nang suait phan li la goc trong nho nhat £ma mat con phan biet dUcrc hai diem.
e = 1' (gia tri trung binh) Cac tat cua mdt va each khac phuc :
Tat cua mat
Mat can
Dac diem
^max < O^
'4\
Mat vi^n f >0V
max
Cach khac phuc . Deo kinh phan kl
. f|^ = - OC^ (kinh sat mat)
. Deo kinh hoi tu
. Tieu ciT CO gia trj sao cho mat deo kfnh nhin gan nhU mat khong tat
Mat lao C, ddi xa mat Deo kinh hoi tu
Tae dung cua kinh nhU vdi mat vien
Hien tUOng lUu anh eua m a t :
Tae dong cua anh sang len mang lUdi con ton tai khoang giay sau khi anh sang tat.
CAU HOI VA BAI TAP
1. Trinh bay cdu tao cua mat ve phuong dien quang hoc.
2. Tnnh bay cac hoat dpng va cac dac diem sau ciia mdt:
- Dieu tiet; - Diem cue vi^n ; - Diem cue can ; - Khoang nhin ro.
3. Neu edc dac diem va each khac phuc doi voi:
- Mdt can ; - Mat vi§n ; - Mdt lao.
Co phai nguoi Ion tuoi thi bi vien thi khong ? Giai thich,
4. Nang suat phan li cua mdt la gi ?
5. Trinh bay su luu anh cua mat va cac iing dung.
Cau tao thu gpn ciia mdt ve phuong dien quang hoc duoc bieu dien nhu so do Hinh 31.11 : 0 : quang tam ciia mdt;
y: diem vang tren mang luoi.
^ Hmh 31.11 Quy udc dat:
Qj: Mdt binh thudng ve gia ;
@ : Mat can ; Q>: Mdt vien.
Hay chon dap an diing cho cac bai tap tu so 6.
den so 8.
6. Mdt loai nao co diem cue viin C^ 6 vo cue ? A. 1 ; . B.'!ằ .
C. 3 . D. T va ® . 7. Mdt loai naoc6f^3j,> OV?
A. 1; . B. (2) .
C. 3' . D. Khong loai nao.
8. Mdt loai nao phai deo kinh hoi tu ? A, :3) . B. (2) . C. @'. D. i: va ® ' .
9. Mdt ciia mot ngudi co diem cue vien C^ each mdt 50 cm.
a) Mdt ngudi nay bi tat gi ?
b) Mudn nhin thay vat 6 vo cue khong dieu tiet.
nguoi do phai deo kinh co do tu bao nhieu ? (Kinh deo sat mat).
c) Diem C(, each mdt 10 cm. Khi deo kinh, mdt nhin thay diem gan nhat cach mat bao nhieu '?' (Kinh deo sat mat).
10. Mpt mat binh thuong ve gia, khi dieu tiet toi da thi tang dp tu cua mat them 1 dp.
a) Xac dinh diem cue can va cue vien.
b) Tinh dp tu ciia thau kinh phdi deo (each mdt 2 cm) de mat nhin thay mpt vat cach mat 25 cm khong dieu tiet.
203
Em CO biet ?
THi NGHIEM DON GIAN VE SU LUU ANH CLJA MAT
Co the thuc hien mot tro chai dan gian nhu sau de chung to hien tugng luu anh cua mdt.
Dung but den ve len mot mat cua tam bia hinh mot cai long chim. Dung but mau ve len mat kia mpt con chim (Hinh 31.1 2). Cho tam bia quay nhanh qua lai.
Quan sat tam bia. Nhan xet va giai thich hien tugng.
Hmh 31.12
3^ KiNHLUP
Trong nhieu truong hgp, con nguai muon quan sat cac vat the, cac chi tiet nho han giai han ma nang sua't phan li cua mIt cho phep.
Vl du, nguai thg sua dong ho muon quan sat cac bp phan cua chiec dong hd deo tay ; chuyen vien phong thi' nghiem sinh hpc muon quan sat cac te bao, cac hong cau, cac vi trung,...
Quang hpc da giup che tao cac dung cu dat dugc yeu cau do.
I - T O N G Q U A T VE CAC D U N G CU Q U A N G B O T R O f C H O M A T
Cac dung eu quang ddu cd tde dung tao dnh vdi gdc trdng Idn hon gdc trdng vat nhidu Idn. Dai lugng dac trung cho tac dung nay la sd bdi gidc, dugc dinh nghia nhu sau :
G = a tana
UQ tan UQ (gdc nhd)
trong dd : a la gdc trdng dnh qua kfnh ; a^ Id gdc trdng vat cd gid tri Idn nha't duge xac dinh trong tiing trudng hgp. Bfl
Ngudi ta phan cac dung cu quang thdnh hai nhdm : - Cac dung cu quan sat vat nhd gdm kfnh lup, kfnh hidn vi,...
- Cdc dung cu quan sat vat d xa gdm kfnh thidn van, dng nhdm,...
II - CONG D U N G V A CAU T A O CUA K I N H LUP
Kfnh lup la dung cu quang bd trg cho mdt de quan sat cac vat nhd (ffiinh 32.1, 32.2, 32.3 vd 32.4).
Hinh 32.1 Kinh liip thdng thudng
K l Sd bdi giac phu thuoc nhdng yeu td nao ?
Hmh 32.2 Kinh liip bo till
2 0 5
Hinh 32.3
Kinh liip dung trong vi phSu thuat
Hinh 32.4 Kinh liip de ban
Hinh 32.5
Mat ngam chirng kinh liip d vd cdc
Hinh 32.6
Kfnh lup dugc ca'u tao bdi mdt thdu kinh hdi tu (hay mdt he ghep tuong duong vdi mdt thdu kfnh hdi tu) cd tidu cir nhd (vai xentimet).
Ill - SU" TAO ANH Bdi KINH LUP
Khi quan sat mdt vat nhd qua kfnh lup, mdt nhin anh do cua vat dd qua kfnh. Mudn the, phdi dat vat nhd trong khodng tir quang tam O cua kfnh ddn tidu didm vat chinh F.
Ngoai ra, dd mdt cd the nhin thay anh thi dnh phai cd vi trf ndm d trong khoang nhin rd ciia mdt.
De thoa man hai didu kien trdn, khi ddng kfnh lup ta phai didu chinh (xd dich kfnh trudc vat hoae nguge lai). Ddng tde quan sat dnh d mdt vi trf xac dinh ggi la ngam chdng a vi trf dd.
Khi cdn quan sdt trong mdt khodng thdi gian ddi, ta ndn thuc hidn each ngdm chirng d diem cue vidn de mdt khdng bi mdi.
IV - SO Bpl GlAC CUA KINH LUP Xet trudng hgp ngdm chiing d vd cue
_ ô ^ tang
^-^ ~ "o ~ tana Ta cd : tana =
0
AS
T
Ngodi ra, gdc trdng vat cd gia tri Idn nha't a^ iing vdi vat dat tai didm cue can C^ (ffiinh 32.6).
AB Dodo :
tana„ = AB OC^
/ AB OCc
f 7
206
C 5 R ^ Hay thiet lap
cdng thiic ciia so Chu y : Ngudi ta thudng Idy khoang cue can Id OC^ = 25 cm. Khi j^^i i^^ |^^l pqgrn san xudt kfnh lup, ngudi ta ghi gid tri cua G^ iing vdi khoang cue chdng d diem cUc
can nay trdn kfnh. can.
Vf du : Cdc kfnh cd kf hieu 3x, 5x, 8x,... se ed tidu cu tuong 25 25 25
img la — cm, — em, — cm,... Chung cd kha nang lam cho gdc 3 5 o
trdng dnh qua kfnh Idn hon ba Idn, nam Idn, tam lan,... gdc trdng true tiep vat.
Bdi tap vi du
Mot nguai co khoang cue can OC^ = 15 cm va die'm C^, a vo cue.
Ngudi nay quan sat mpt vat nho qua kfnh liip co tieu cu .5 cm. Mat dat each kfnh 10 cm.
a) Phai dat vat trong khoang nao truoc kfnh ?
b) Tfnh so boi giac eiia kfnh trong trucmg hop nguoi nay ngdm chimg d vo cue.
Gidi
a) KIwdng dgt vdt
Khoang phai dat vat la MN sao cho anh ciia M, N qua kfnh liip lan luot la cac diem C^ d GO va Q .
Ta CO : d^ = - O^C^, = - co Suy ra : d^ = f = 5 cm.
d^ = - O^f^ = - 5 cm
Tit do : d^= ^ = = 2,50 cm.
dn-f - 5 - 5
Khoang phai dat vat la khoang gioi han bdi : 2.50 cm < <:/ < 5 em, b) So hgi gidc
Ta CO cong thuc : G^ = ^ Vay : G^^=j = 3.
Dung cu quang bo t r d cho mat deu tao anh ao co goc trong Idn.
. . . ., ^ a tan a So DOI giac : G = ô --
• ^ Cp tan a^
Kinh lup la thau kinh hoi tu co tieu cU nho (vai xentimet).
So boi giac cua kinh lup khi ngam chirng d vo ciTc : G^ =
T
207
CAU HOI VA BAI TAP
1. Cac dung cu quang bo tro cho mat co tac dung tao anh ra sao ? Dinh nghia sd boi giac.
2. Kinh lup CO cau tao nhu the nao ?
3. Ve duong truyen ciia chum tia sang ung vdi mdt ngdm chung kinh lup d vo cue.
Viet cong thuc sd boi giac ciia kinh lup trong trudng hop nay
Ve so do tia sang trong trudng hgp mdt ngdm chung kinh liip 6 vo cue de tra Idi cau hoi ciia bai tap 4 va 5 duoi day
Yeu to nao ke sau khong dnh hudng den gia tri ciia so boi giac ?
A. Kich thuoc ciia vat.
B. Oac diem ciia mdt.
C. Dac diem ciia kinh liip.
D. Khong co (cac yeu to A, B, C deu anh hudng).
Tiep theo bai tap 4.
Cach thuc hien nao sau day van cho phep tiep tue ngdm chung 6 vo cue ?
A. Ddi vat.
B. Ddi thau kinh.
C. Ddi mdt.
D. Khong each nao.
Mpt hgc sinh can thi co cac diem C^, C^ each mdt lan lugt 10 cm va 90 cm. Hgc sinh nay dung kinh lup co do tu +10 dp de quan sat mgt vat nho. Mdt dat sat kinh.
a) Vat phai dat trong khoang nao trudc kinh ? b) Mgt hgc sinh khac, co mdt khong bi tat, ngdm chiing kinh liip ndi tren d vo cue. Cho OC^ = 25 cm. Tinh so boi gidc.
208
<5<5 K I N H HIEN VI
Kinh hien vi xuat hien lan dau a Ha Lan vao khoang cuoi the ki XVI a clang tho sa. Ngay nay, kinh hien vi co the giup nguai ta quan sat va ehup anh dugc nhung vat the cue nho nhu : cac te bao, cac vi khuan... (Hinh 33.1 va 33.2).
I - CONG DUNG VA CAU TAO CUA KINH HIEN VI Kfnh hid'n vi la dung cu quang bd trg cho mdt dd quan sat nhirng vat rdt nhd, bdng cdch tao dnh cd gdc trdng Idn. Sd bdi gidc cua kfnh hien vi Idn hcfn rat nhieu so vdi sd bdi giac cua kfnh lup.
Kinh hien vi cd hai bd phan chinh :
, Vdt kinh Lj la mdt thdu kfnh hdi tu (thuc ra la mdt he thdu kfnh tac dung nhu thdu kfnh hdi tii) cd tidu cu rat nhd (cd milimet).
. Thi kinh L2 la mdt kfnh lup dung dd' quan sat anh cua vat tao bdi vat kfnh.
Hai bd phan chfnh nay dugc gdn 0 hai ddu mdt d'ng hinh tru sao cho true chfnh cua chung trung nhau vd khoang each giiia chung OJOT - I khdng ddi (ffiinh 33.5).
Ngudi ta ggi F\F-, ^SVadp ddi quang hoc cua kfnh.
Ngoai ra cdn cd bd phan tu sang de chidu sdng vat cdn quan sdt. Dd thudng la mdt guong cdu 1dm.
II - SU" TAO ANN Bdi KINH HIEN VI
Vat kfnh cd tac dung tao anh that A,'5j Idn hon vat AB vd d trong khoang 02^2 ^^ quang tam den tidu didn vat cua thi kfnh.
Hinh 33.1 Kinh hien vi tho sd d thdi ki dau
Hmh 33.2 Kinh hien vi ngay nay
14. VATL|11(C)-ST-A
•••*=*
j?^¥)r;
Hinh 33.3
Tieu ban de quan sat qua kinh hien vi
Hinh 33.4
Dieu chinh kinh hien vi diing 6c vi cap H ] Tai sao phai kep vat gida hai ban thuy tinh mong khi quan sat vat bang kinh hien vi ?
Thi kinh tao dnh do sau cung A^^B', Idn hem vat nhieu Idn va nguge chidu so vdi vat AB.
Mdt dat sau thi kfnh dd quan sdt se nhin thay anh AJB^ *^^^ ^^^ AB tao bdi kinh hien vi.
Anh sau cung A^fi; phdi dugc tao ra trong khoang nhin rd cda mdt. Do do phdi dieu chinh kinh dd thay ddi khoang each d^ tir vat AB ddn vat kinh Oy
Ddi vdi kfnh hien vi, ung vdi khoang C^C^ cua dnh thi khoang Ad^ xd dich vat thudng hd't siic nhd, khoang vai chuc micrdmet.
Do dd trong thuc te khi quan sdt vat bdng kfnh hien vi phdi thuc hidn nhu sau :
- Vat phdi la vat phang kep giua hai tdm thuy tinh mdng trong sud't. Dd la deu bdn (ffiinh 33.3). R l - Vat dugc dat cd dinh trdn gid. Ta ddi toan bd d'ng kfnh tir vi trf sdt vat ra xa dan bdng dc vi cdp (Hinh 33.4).
Ndu anh sau cdng A^B!, ciia vat can quan sat dugc tao ra d vd cue thi ta cd su ngdm chiing kfnh d vd circ (ffiinh 33.5).
Hinh 33.5 Dudng truyen c
kinh hien vi duac ngSm chUng d vd cue B
A. 1
/ '^^^*^
(") A F,
^hiim tia sang q ua N
/ / -
F\
8 I
F2 I A\
B
B'z
^
1
O2
' • ' ' , . A
\
1
( o = ) . - -
210