HOANG KHANH (Hd Nii)
cao hon. C6c quang ph6 b6c cdng cao thi cing
tld l6n nhau nhi6u hon. Tpi m6i Oiem 6 xa vdn tr8ng ffung tdm thi cO rit nfridu cuc dpi cua cdc vdn s6ng trins nhau nOn sE tao ra c6c vdn mdu
trlng nhd nhd ggi ld vdn trlng bQc cao.
Trong c6c d6 thi thuong y6u cAu tinh b6 rQng
quang ph6, x6c dinh tai mQt vi tri c6 bao nhi6u
^ .r..
v6n s6ng, vdn t6i trung nhau o d6.
*Thi dg l. Trong thi nghi€m cua Y-dng vi
giao thoa dnh sdng, khodng cdch giira hai khe
/d 0,8mm, khodng cdch tir hai khe d€n ntan
ld 2m. Dilng dnh sdng trdng (0,76pm 2 )" 2
0,38prm) dA chi€u s"ang hai khe. Xac dinh bi
r6ng cua quang ph6 bdc I vd bqc 2.
Ldi gidi Ap dung c6ng thric dd n6u d fr6n ta c6:
D
Ar1 :.1561 -xrtr :1 Q4- h)
a
_ 2000 ,n _.: :
ffi (0, 76 _ 0,38)t o-3 : o,95mm
Lx2:2Lx1:1,9mm.
*Thi du 2. Trong thi nghiQm Y-dng vi giao thoa anh.sang. hai khe duqc chidu biing anh
sang trdng co buctc song tir 380nm d)n760nm. Khoang cach giira hai khe /d 0,8mm, 760nm. Khoang cach giira hai khe /d 0,8mm, khodng cdch t* m\t phang chaa hai khe d€n
mdn ld 2m. Xdt m6t di€m tr€n mdn tqi vi tri
cdch vdn trung tdm 5mm. Hdi:
a) Cd vdn sdng ctia nhrtng bac xa ndo trilng
vdo d6?
b) Co vdn ii cila nhfing btbc xa ndo trilng
vdo d6?
t.u nhu t)n,.ta thdy c69, vdn bQc 2 cin cfuc 6nh s6ng tlon sdc cfing s[p x6p tpo thdnh quang ph6 bpc hai. B6 rQng quang ph6 bQc 2:
A xz: xsd2 - xsa: 2 A, xt.
O quang ph6 bpc 3 c6 nhirng vi tri vAn s6ng
cira n6 firing v6i vdn sSng cria quang ph6 bac
TORN HoC...o clirdiE;e o clirdiE;e . ).D xM: xs: k- ^ cLXtt 0.8.10-3.5.10-3 +/- </v- kD - n #r>
Md ), phii thoa min di6u kien 380.10-em < ). < 760.10-e m
2.to-6
=380.10-e =+<760.rc-e
o2,6<k<5,2>k:3;4;5.
Thay c6c gi6 fr ctn k vi-o (1), ta c6 ba bric xp tumrg rmg ld
lrD ).D\=hL llaLZa x.>=k.r. \=hL llaLZa x.>=k.r.
Hai vdn s6ng tr6n tring nhau h,hi 4: x2
)rD )^D
e\ o =kz-?e\\=kil,t
.h5ak,r=k, ' =- t 'L2 4'k, ak,r=k, ' =- t 'L2 4'k,
Vi frr vd kzldhai sO nguy6n ndn hQ thric tr6n
thoi mf,n khi tr1 h bQi s6 oha 4, tuc ld h:* 4;
+8i + 12; + 16... e Vi fii ting nhau hn deu
dg, *g vot kl: +4. Hai vi tri trtng nhau l6n d0u ti6n cSch v6n trung tdm ld
xt : kt42 -4'o's'tgu 'z : 4. ro t (-) : 4 (mm)
a 10-'
*Thi du 4. Trong th{ nghiQm Y-6ng vi giao thoa dnh sang. Khodng cach gilra hai khe ld
a : 0,8mm. Khodng cdch ti.r hai khe ddn mdn
ld D:1,2m. Ng.rdi ta chi€u ding thdi hai btrc
xa don sdc co buoc song )1=0,45pm vd
1z:0,75pm.
a) Xac dinh vi trl trilng nhau cila hai vdn sang. b) Xac dinh vi tri trung nhau cua hai vdn di.
Ldi gi,fii
Dtr, Dl,
il :-' :0,675mm',iz: ' : l,l25mm.
aa
a) Vi tri trtng nhau cira hai vAn s6ng: xr: kj1
: k2i2- ktlr: kzlz> kr:h.fr:I .t,
Al 5
= Vi kr nguy6n ndnk2phtih bQi s6 cira 3. Ta d4t lrz:3n v6 n: 0, +1, +2,.. . Do d6
5
k, : i 3n: 5n vu n : 0, +7, +2,...
5
VQy vi fficdc vdn sring tn)ng nhau ld
xr: lcziz: 1,1.25.3n(mm) : 3,375n (mm)
v0in:0, +1, +t,...
b) Vi tri trdng nhau cria hai vdn t5i: qcr+ l)ir: i2&r++) 2k, +l i, 2k, +1 5 =...:- ' 2kr+1 ir " 2kr+l 3 Vikr vd kzldsbnguydn n)n 2kr+lvd Zkr+l h sO le, do d6 tI[t 2kr+1: 5(2n+1) thl 2k, +L :3(2n + 1) voi n: 0, +t, +2, ...
b).C6c bric xp cho vdn t6i tAi xlaphii th6a mdn di6u kiQn: .. _. 2D xM: &: (f + U,5)-'a ) 1= ffiM _ 0,8.10-'.5.10- (k+0,5)D (k+0,5)2 ffiM _ 0,8.10-3.5.10r (2) Md Zphdi th6a mdn tliAu kiQn:
380. 10-em< ). 3 7 60.10-e m
2.rc-6
=380.10 ,=ffi< 760.10-e
e2,1<k<4,7 >k=3;4.
Thay cilc ei fr cira fr vdo (2) ta c6 hai bric xa
tucrng img ld
DANG 2. Biti tSp hiQn tuqng giao thoa cfra 6nh sing h6n hqrp gdm hai 6nh sfng tlmr sic.
Ifhi chi6u chim s6ng SQm hai 6nh sring don
sic vdo khe Y-dng thi m6i 6nh s6ng don sic sE
cho mQt hQ v0n. TrCn mdn thu duoc ba loai vdn s6ng ld vdn c6 mdu cta 6nh sring don sic m6t vd 6nh s6ng tlcrn sEc hai, vdn c6 mdu ld mdu t6ng hqp cria hai 6nh s6ng tlon sic do hai v6n s6ng cria chring trtng nhau.
*Thi dr1 3. Trong thi nghiQm Y-ing vi giaothoa anh sdng. Khodng cdch giira hai khe ld thoa anh sdng. Khodng cdch giira hai khe ld
a : lmm. Khodng cach tir hai khe d€n mdn ld