Cu 18: Trnh by hiu ng Compton

L Thuyt Quang - 14 -

Cu 18: Trnh by hiu ng Compton ? Tr Li:

Th nghim: Chiu tia X vo than ch => b tn x (lch khi phng truyn thng)

Cc quy lut:

+ Nu nguyn t ca cht tn x nh th tn x mnh v ngc li.

+ Cng ca tia tn x t l vi gc tn x

: gc tn x.

Gii thch nh tnh:

+ Khi va chm vi electron ca nguyn t th lch khi phng truyn thng th b tn x.

+Khi va chm n mt nng lng do truyn mt phn nng lng cho electron m nng lng li t l nghch vi bc sng

Cu 17:Trnh by thuyt lng t nh sng v dng thuyt lng t nh sng gii thch cc nh lut quang in ?

Tr li: Thuyt lng t nh sng. (thuyt photon)

nh sng khng nhng c bc x m cn b hp th v truyn i thnh tng lng nng lng gin on gi l lng t nh sng.

_ Mi photon c nng lng xc nh:

h = 6.625

_ Cng thc Anhxtanh

+ Mi photon ca chm sng ch tng tc vi 1 electron t do ca kim loi v photon truyn ton b nng lng ca mnh cho (e). (e) chuyn ng trn b mt kim loi tiu ph ht 1 phn nng lng l . Dng 1 phn nng lng sinh cng thot l A, phn nng lng cn li to thnh ng nng ca (e) .

AD nh lut bo ton nng lng:

Vi nhng (e) ngay mt kim loi th = 0 suy ra ng nng ln nht suy ra

Gii thch cc nh lut quang in. _ V gii hn quang in:

+ T cng thc Anhxtanh: => hiu ng quang in ch c th xy ra khi

hay

t (: gii hn quang in: tn s nh nht ca nh sng cn c th gy ra c hiu ng quang in)

Bc sng: v

_ V ng nng ban u chuyn ng hay hiu in th hmC:

_ V dng in bo ho.

+ Theo thuyt lng t th cng chm sng ri vo kim loi c xc nh bi s photon ti trong 1 n v thi gian, trn 1 n v din tch ca mt kim loi.

Vy s (e) n c gii phng khi kim loi trong 1 n v thi gian t l vi s photon n ti mt kim loi trong khong thi gian

Trong E l nnng lng chm sng v t l vi I

n ~ n m n~ E v E ~ I => n ~ I

Cu 16: Trnh by hin tng quang in ngoi v cc nh lut quang in

Tr li

Hiu ng quang in ngoi.

_ Hiu ng quang in ngoi l s gii phng e khi b mt ca 1 vt di tc dng ca nh sng. N c th xy ra vt rn, lng, kh.

_Th nghim:

+ Anot v catot c t trong bng chn khng (p sut ) c ca s quang hc bng thch anh F+Catt K c lm bng kim loi cn nghin cu hin tng quang in. 2 in cc A, K c ni vi ngun in 1 chiu P. Hiu in th gia hai in cc c th thay i nh bin tr R

+Khi ri vo K bng 1 chm nh sng n sc c bc sng thch hp, cc e s c gii phng khi K v chuyn di v A di tc dng ca in trng , to thnh d trong mch v s c xc nh bng in k G. Dng in ny c gi l dng quang in cn cc e c bt ra khi K bi tc dng ca nh sng th gi l quang e. KLun: Cng dng quang in tng khi tng cng nh sng ri vo bn K

in tch c gii phng ra khi K l in tch m.

_ng c trng Vn_ampe

+ Khi hiu in th U gia hai cc thay i th dng quang in cng thay i. ng cong biu din s ph thuc ca cng dng quang in vo hiu in th U

(= f (U)) gi l ng c trng Vn_ampe.

+Khi dng quang in khng thay i, gi tr ln nht ca dng quang c gi l dng quang in bo ho.

( n: s e c gii phng khi K trong 1s)

+Khi U = 0 vn c dng in v n ch bng 0 khi U c 1 gi tr m ph thuc bn cht kim loi v tn s (bc sng) ca nh sng ri vo K

e: in tch

m: khi lng Cc nh lut quang in.

_nh lut v dng in bo ho (nh lut Xtltp)

Khi tn s ca nh sng ri vo catot khng i, cng dng quang in bo ho t l vi cng ca chm sng m catot nhn c

C => n ~ I

Pht biu khc: s e c gii phng khi K trong 1 n v thi gian t l vi cng I ca chm sng m K nhn c.

_nh lut v vn tc ban u chuyn ng ca quang e.

+Vn tc ban u chuyn ng ca quang in e khng ph thuc vo cng ca chm sng ri vo K m ch ph thuc vo tn s ca chm nh sng .

+Tn s cng ln th vn tc cng ln._ nh lut v gii hn quang in.

i vi mi kim loi xc inh, hiu ng quang in ch xy ra khi tn s (hay bc sng ) ca chm sng ri vo bn kim loi ln hn 1 gi tr (hay nh hn 1 gi tr) ca kim loi

Cu 15: Trnh by thuyt lng t nng lng cng thc Plng?

Tr Li.

_ Bc x in t c pht ra di dng nhng nng lng ring r. c gi l lng t nng lng v c nng lng c xc nh bng cng thc

Nng lng ca bc x: E = n

_Cng thc Plng.

Cu 14: Cc nh lut bc x ca vt en tuyt i. Tr li.

Vt en tuyt i: l vt hp th tt c cc bc x in t. trong thc t ta ko h c vt en tuyt i. Nn ta ch c vt gn ging vt en tuyt i v ta coi nh l vt sng.

Bc x nhit: l bc x do mi vt c nhit khc 0 (Kenvin) pht ra. c im ca bc x nhit l bc x cn bng.

nh lut Stephan _ Bolzoman.

= 5.7.

trng nng lng t l vi lu tha bc 4 ca nhit tuyt i.

nh lut Vin.

_ Vin I :

b = 2.,9.

Bc sng ng vi nng sut pht x cc i ca vt en tuyt i t l nghch vi nhit tuyt i_ Vin II:

B = 1,03.

Nng sut pht x n sc ca vt en tuyt i t l v lu tha bc 5 ca nhit tuyt i.

Cu 13: S tn x ca nh sng.

Tr li. Hin tng: Khi nh sng truyn trong mi trng trong sut v ko ng tnh th nh sng b lch khi phng truyn thng c gi l hin tng tn x nh sng.

Mi trng vn c:

Nx: + Nu chm tia ti l nh sng trng th ta thy nh sng c bc sng cng ngn cng b tn x nhiu (iu ny gthch htng bu tri c mu xanh)

+ nh sng tn x l nh sng phn cc 1 phn. Nu xt tia tn x theo phng vung gc th b phn cc thng

+Cng sng tun theo cng thc

+ nh lut Rely

Cng ca chm nh sng tn x t l nghch vi lu tha bc4 ca bc sng nh sng Vi mi trng tinh khit Thc nghim cho thy ngay vi mi trng trong sut cng xy ra hin tng tn x. Nguyn nhn do s thng ging mt mi trng.

Cu 12: Trnh by s hp th nh sng.

Tr li_ L hin tng gim cng nh sng khi truyn trong 1 mi trng.

_ Gii thch: di tc dng ca in trng ca nh sng cc e ca nguyn t thc hin dao ng cng bc vi tn s bng tn s ca nh sng t. e dao ng pht sng th cp. Sng th cp giao thoa vi sng ti to thnh sng tng hp lan truyn trong mi trng v c bin nh hn bin ca sng ti dn n cng nh sng i qua mi trng b thay i. Nng lng ca s gim bin sng ti l do nguyn t hp th 1 phn nng lng ca nh sng ti.

Vi cc e t do n c kh nng hp th ton b nng lng ca sng nh sng ti. V vy vi cc kim loi mng nh sng cng khng truyn qua c.

_ Gi s cng nh sng chiu ti l , lp dy l , k l h s hp thTa c: => nh lut Bughe

Cng nh sng truyn qua 1 mi trng hp th gim theo nh lut hm s m. Nu mi trng l dung dch c nng cht ho tan l c

l h s hp th trn 1 n v nng .

_ nh lut Bughe Bia

Cu 11: Trnh by s tn sc nh sng?

Tr li.

*Th nghim: chiu nh sng trng vo lng knh thy nh sng b tch thnh di -> tm => hin tng tn sc nh sng.

s ph thuc ca chit sut vo tn s

*Dng thuyt e gii thch hin tng tn sc.

_ xt 1 khi in mi trong sut ch cha 1 loi nguyn t, mi nguyn t ch cha 1 loi e c kh nng dao ng cng bc_Chiu 1 nh sng n sc vo mi trng

e chu lc cng bc (lc in t) c ln e.E

_Gi s bn thn e c 1 dao ng ring => chu tc dng ca lc hi phc bng (-kx)

Khi dao ng trong nguyn t b cn tr bi cc e khc khin cho dao ng trn h tt dn, lc lm dao ng khc tng dn c ln (-gx)

Phng trnh nh lut II cho e c

Chia c 2 v cho m ta c;

_ Nu b qua ma st: g = 0

_ Phng trnh c dng:

Trong theo in ng lc hc ta c:

=>

N: s nguyn t trn 1 n v th tch.

n ph thuc => dng thuyt e gii thch c hin tng tn sc.

Cu 10: Trnh by s phn cc nh sng do lng chit.

Tr li.

*Th nghim:

_Kho st s truyn nh sng qua tinh th bng lan. Th nghim cho thy rng trong tinh th bng lan c 1 phng c bit duy nht khi cho tia sng truyn theo phng n s ko b tch ra thnh 2 tia. Phng c bit c gi l trc quang hc ca tinh th.

_Nu chiu 1 tia sng t nhin khng trng vi trc quang hc th thc nghim cho thy n b tch thnh 2 tia. 1 tia c gi l tia thng truyn thng tia khc x l tia bt thng_Thc nghim cho thy c 2 tia u l phn cc thng nhng chng phn cc trong 2 mt phng vung gc vi nhau. Vi tia bt thng vecto trng mt phng cha trc quang hc v tia thng. cn vi tia thng vung gc.

*Gii thch hin tng.

_L do s ph thuc ca chit sut ca tinh th vi cc tia l khc nhau (hin tng ph thuc chit sut l hin tng lng chit)

_Phn tch vecto sng thnh 2 vecto vung gc : vecto sng ca tia bt thng : vecto sng ca tia thng.

Cng sng ca 2 tia.

Thay i gc ti i ca tia ti, o gc khc x

+i vi tia thng chit sut ko i:

+i vi tia bt thng

_ Chit sut ph thuc vo phng truyn. Dn n cng ph thuc vo phng truyn. Nu < vn tc tia thng th ta c tinh th dng vi

Nu > vn tc tia thng ta c tinh th m vi .

Cu 9: S phn cc nh sng v s phn cc nh sng do s phn x v khc x ?

Tr li.

S phn cc nh sng.

_nh sng t nhin.

+ nh sng l sng in t, sng ngang c vect vung gc vi phng truyn sng+ Bnh thng vi nh sng t nhin dao ng u theo mi phng

_Bn phn cc.

+Thng thng l nhng bn tinh th trong sut m khi cho nh sng truyn qua th nh sng tr thnh nh sng phn cc

vd: bn Tuamalin, tinh th bng lan,.

+ Mt phng cha vecto c gi l mp dao ng, mp vung mp dao ng c gi l mp phn cc_Hin tng bin nh sng t nhin thnh nh sng phn cc c gi l s phn cc nh sng.

_Gthch s phn cc nh sng (truyn qua Tuamalin)

+Do nh sng l sng ngang nn E vung gc vi phng truyn sng. M bn Tuamalin ch cho truyn qua nhng vt trng trc quang hc v gi li nhng vt vung gc vi trc quang hc S phn cc nh sng do phn x v khc x

_Xt 1 tia ti mt phn cch ca 2 mi trng c chit sut khc nhau (vd: kk v nc)

_Nghin cu v tia phn x v khc x thy chng u l nh sng phn cc 1 phn v thc nghim cho thy vi tia phn x vt dao ng u tin theo phng ca mt phng ti cn tia khc x cng l phn cc 1 phn nhng phng trng mt phng ti.

_Khi thay i gc ti i n gi tr th tia phn x v khc x vung gc vi nhau lc ny tia phn x v khc x tr thnh phn cc thng (ton phn) vi ca tia phn x vung gc vi mt phng ti, ca tia khc x trng vi mt phng ti_Theo nh lut khc x ta c:

=> nh lut Briuxto

Cu 8: Trnh by v cch t nhiu x.Tr li.

Nhiu x sng phng

_ Sng phng l sng c mt u sng l mt phng hay cc tia sng trong chm sng song song vi nhau. Tc l ngun sng coi nh t v cng_Cch t nhiu x l h thng gm nhng khe hp c cng rng t song song v cch u nhau

+ Phn loi: - cch t truyn qua.

- cch t phn x.+Cc i lng c trng: - chu k cc t b: l hnh chiu gia 2 khe hp gn nhau lin tip

s khe trn 1 n v di l: thng ly l=1 =>

Khi nh sng truyn qua khe cch t n b nhiu x bi cc cch t v nh sng thu c trn mn quan st l tng hp ca nh sng b nhiu x ca tt c cc khe. iu kin quan st c chuyn ng nhiu x bc k l:

Nhiu x trn mng tinh th

_Mng tinh th l s sp xp c trt t ca cc tinh th trong khng gian. Do khong cch gia cc nguyn t l nh nn ta c th coi mng tinh th nh l 1 cch t c chu k rt nh. V tr cc cc i nhiu x c x/ bi cc /k => /k Vunfo-Brag Trong : k l bc ca nhiu x

l gc chiu ti

d l hng s mng

_ng dng; nghin cu cu trc mng cho ta bthc mng ny l mng ca cht ji` v d on c tnh cht vt l ca n.

Cu 7:Trnh by v s nhiu x ca sng cu qua 1 mn chn trn v qua 1 l trn

Tr li.

Nhiu x qua 1 l trn.

Xt s truyn nh sng t O ti P qua l trn AB. V mt cu tm P da vo l AB. T P l tm v cc i cu Fresnel trm i cu , gi s l cha n i. Bin thnh phn in trng tai P s l:

Ly du + nu l s l, du nu l s chn.Ta sp xp li biu thc:

T (6.1) ta rt ra:

Kt lun:

1. Khi khng c mn chn hoc l c kch thc ln th , nn cng sng ti P s l:

2. Nu l cha mt s l i th

Tc l im sng P s sng hn so vi khi khng c mn chn. c bit khi c mt i th:

Nhiu x do 1 mn trn( hay mt a trn)

t gia ngun sng im O v im quan st P. mt a trn c bn knh . Gi s a che mt m i Fresnel u tin, khi bin cng in trng tng hp ti P l:

Cc biu thc trong du ngoc bng khng v s i tin ti v cng, nn:

Ta thy: mc d b che khut, nhng cng sng ti P vn khc 0

Cu 6: Trnh by phng php chia i FresnelTr li

_Xt s truyn nh sng t 1 ngun sng im O ti 1 im P. Do S l ngun sng im nn mt u sng l mt cu. Xt 1 mt u sng cch ngun S 1 khong l R. Ly P lm tm quay bn knh

Notes: 2 i lin tip nhau 1 khong nn c bin ngc pha nhau

Din tch i th n:

Trong l bn knh , ,

Nn:

Ta c: =

Ly vi phn hai v ta c: 2rdr = 2R(R+b)sind

V nn b qua

Ta c: Rsin d= rdr/(R+b) trong dr =

Thay vo biu thc ca din tch dSn ta c

vy din tch ca mi i cu khng ph thuc vao n, nn cc i cu c din tch bng nhau.Tnh bn knh ca cc i cu:

rt nh, nn:

Trong tam gic ta c:

: bn knh i th k

Vy bn knh i cu t l vi

Theo nguyn l Huyghen, mi i xem l mt ngun th cp. gi nh sng ti P. Do din tch bng nhau nn cng sng ca mi i l nh nhau, cc i ny tha mn cc iu kin kt hp, nn chng s giao thoa vi nhau. Thnh phaand in trng E ti P s l tng hp ca cc cng in trng tng i gi ti P. Gi Eon l bin in trng ca i th n gi ti P. Khi n tng ln, cc i cu cng xa P. nn gc nghing gim dn, nn cng in trng cung gim dn, nn:

Tuy nhin gim rt chn, nn bin cng gim rt chm. nn c th coi:

(6.1)Mt khc do hai i cch nhau khong , nn lch pha gia hai i s l:

( chng ngc pha nhau)

Vy thnh phn in trng tng hp ti P s l:

_Nu s i l l th:

_Nu l s chn i :

-Nu nh sng ko b chn th k = => = 0 v

Cu 5: Hin tng nhiu x nh sng v dng nguyn l huyghen_Fresnel gii thch h.tng nhiu x nh sng

Tr li.

Hin tng nhiu x nh sng

_Theo quang hnh hc th trong mi trng ng tnh nh sng truyn thng. Tuy nhin thc nghim chng t rng iu ko phi bao gi cng ng._Ta xt 2 th nghim sau:

T/no1: cho a/s t 1 ngun a/s im S bk chiu ti 1 l trn nh trn 1 ming ba. Pha sau ming ba t 1 mn E. Nu l nh th bn ch trng ti xhin nhng vt sng ti xen k nhau

Vy nh sng trng TH ny ko tun theo nh lut truyn thng

T/no2: t 1 dy kim loi mnh song song vi 1 khe sng. Sau on dy t mn quan st E // vi on dy.

_Theo nh lut truyn thng th min AB b che khut bi si dy phi l min ti v ngoi min d phi c ri sng u. Tuy nhin ti im M nm trn trc i xng ca AB trong min ti ta vn thy c nh sng ln cn cc im A ta vn thy cc vn ti v sng xem k nhau. R rng y nh sng cng ko truyn thng htng a/s b lch khi phng truyn thng khi i qua gn mp nhng vt chn sng c gi l nhiu x nh sng

Nguyn l Huyghen_Fresnel.

_ gthik htng nhiu x as ngi ta coi as l sng. Ngl Huyghen cho ta gthik nh tnh htg nhiu x cn ngl Fresnel b sung cho ta gthik tnh nh lng_ Nguyn l Huyghen.+ Nd: Ti mi im trn phng truyn sng c th tr thnh cc ngun pht sng th cp v tip tc pht a/s v pha trc n+ gthik nh tnh: ti cc im trong vng trng ti s c sng a/s gy bi ngun th cp truyn n. N s l im sng nu hiu quang trnh gi n v im ti nu hiu quang trnh

_Nguyn l Fresnel

Pha v bin dao ng ca cc ngun th cp l pha v bin d ca ngun gi n vtr ca ngun th cp.

Cu 4:Thnh lp cng thc tnh khong vn trong th nghim giao thoa ca lng thu knh Bi

Tr li.

Ta c (e rt nh)

_Xt 2 tam gic ng dng c

_Li c:

Cu 3: Thnh lp cng thc tnh khong vn trong trng hp th nghim giao thoa ca gng Fresnel

Tr li.

_Dng c gm 2 gng t nghing 1 gc . Ngun sng S t trc 2 gng. Qua cho nh , qua cho nh ,

EMBED Equation.DSMT4 o, gn nhau v l 2 ngun kt hp_Hai chm tia sng phn x trn 2 gng gp nhau v giao thoa vi nhau. Mn E t trong trng giao thoa s quan st c vn giao thoa

_khong cch S n I: a

E n I : l nh n mn E: D= l+a

V rt nh nn d=2.a

=>

Cu 2: Thnh lp cng thc tnh khong vn trong trng hp th nghim giao thoa ca lng lng knh Fresnel

Tr li

_K/c t S-> lng knh; a

Lng knh-> mn: l k/c t nh n mn E: D=a+l -V lng knh c gc chit quang nh nn gc lch gia tia ti v tia l khi truyn qua lng knh l

Ta c:

Cu 1:Trnh by hin tng giao thao nh sng v thnh lp cng thc tnh khong vn

Tr li.

Hin tng giao thoa nh sng

_A/s l sng in t c bc sng nm trong khong

_Gthoa l s tng hp ca 2 hay nhiu sng kt hp m kt qu l to ra trong trng giao thoa nhng im sng, ti xen k nhau

Vng sng l vng nh sng c tng cng, vng ti l vng nh sng b trit tiu

_Sng a/s kt hp l sng tho mn: cng tn s, lch pha khng i theo thi gian.

Thnh lp cng thc tnh khong vn

_Xt 2 ngun k/hp , t cch nhau 1 khong d_t 1 mn E cch 2 ngun k/hp 1 khong D. Xt s giao thoa ti 1 im M trn mn quan st cch , ln lt l

_Coi mi trng l khng kh, chit sut n = 1

-Ta c

-Nu ti M l vn sng =>

=>

_Nu ti M l vn ti =>

=>

-Khong vn: khong cch gia 2 vn sng, vn ti lin tip:

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