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GV: an Vn Lng Email: [email protected] ; [email protected] Trang 1

CHUYN : LNG T NH SNG A. TM TT L THUYT

I. Hin tng quang in(ngoi) - Thuyt lng t nh sng. a. Hin tng quang in Hin tng nh sng lm bt cc electron ra khi mt kim loi gi l hin tng quang in ngoi (gi tt l hin tng quang in). b. Cc nh lut quang in + nh lut quang in th nht (nh lut v gii hn quang in): i vi mi kim loi nh sng kch thch phi c bc sng ngn hn hay bng gii hn quang in 0 ca kim loi

, mi gy ra c hin tng quang in: 0.

+ nh lut quang in th hai (nh lut v cng dng quang in bo ha): i vi mi nh sng thch hp (c 0), cng dng quang in bo ha t l thun vi cng chm nh sng kch thch. + nh lut quang in th ba (nh lut v ng nng cc i ca quang electron): ng nng ban u cc i ca quang electron khng ph thuc vo cng ca chm sng kch thch, m ch ph thuc vo bc sng nh sng kch thch v bn cht kim loi. c. Thuyt lng t nh sng + Chm nh sng l chm cc phtn (cc lng t nh sng). Mi phtn c nng lng xc nh (nng lng ca 1

ph tn = hf (J). Nu trong chn khng th

ch

fh.

.

f l tn s ca sng nh sng n sc tng ng. h=6,625.10-34 J.s : hng s Plank; c =3.108 m/s : vn tc nh sng trong chn khng. + Cng chm sng t l vi s phtn pht ra trong 1 giy. + Phn t, nguyn t, electron pht x hay hp th nh sng, ngha l chng pht x hay hp th phtn. + Cc phtn bay dc theo tia sng vi tc c = 3.108 m/s trong chn khng. + Nng lng ca mi phtn rt nh. Mt chm sng d yu cng cha rt nhiu phtn do rt nhiu nguyn t, phn t pht ra. V vy ta nhn thy chm sng lin tc. +Phtn ch tn ti trong trng thi chuyn ng. Khng c phtn ng yn. d. Gii thch cc nh lut quang in

+ Cng thc Anhxtanh v hin tng quang in: hf =

hc= A +

2

1mv

2

max0 .

+ Gii thch nh lut th nht: c hin tng quang in th nng lng ca phtn phi ln hn hoc bng cng

thot: hf =

hc A =

0

hc 0;

-vi 0 l gii hn quang in ca kim loi: 0 = A

hc

-Cng thot ca e ra khi kim loi : 0

.

chA

-Tn s sng nh sng gii hn quang in : 0

0

cf

vi : V0 l vn tc ban u cc i ca quang e (n v ca V0 l m/s)

0 l gii hn quang in ca kim loi lm catot (n v ca 0 l m; m; nm;pm)

m (hay me ) = 9,1.10-31 kg l khi lng ca e; e = 1,6.10-19 C l in tch nguyn t ; 1eV=1,6.10-19J. +Bng gi tr gii hn quang in

Cht kim loi o(m) Cht kim loi o(m) Cht bn dn o(m)

Bc 0,26 Natri 0,50 Ge 1,88

ng 0,30 Kali 0,55 Si 1,11

Km 0,35 Xesi 0,66 PbS 4,14

Nhm 0,36 Canxi 0,75 CdS 0,90

e. Lng tnh sng - ht ca nh sng +nh sng va c tnh cht sng, va c tnh cht ht. Ta ni nh sng c lng tnh sng - ht.

Ibo ha

I

O Uh U

Welcome PCNew Stamp


+Trong mi hin tng quang hc, nh sng thng th hin r mt trong hai tnh cht trn. Khi tnh cht sng th hin r th tnh cht ht li m nht, v ngc li. +Sng in t c bc sng cng ngn, phtn c nng lng cng ln th tnh cht ht th hin cng r, nh hin tng quang in, kh nng m xuyn, kh nng pht quang,cn tnh cht sng cng m nht. +Tri li sng in t c bc sng cng di, phtn ng vi n c nng lng cng nh, th tnh cht sng li th hin r hn nh hin tng giao thoa, nhiu x, tn sc, , cn tnh cht ht th m nht.

II. Hin tng quang in trong. a. Cht quang dn Cht quang dn l nhng cht bn dn, dn in km khi khng b chiu sng v dn in tt khi b chiu nh sng thch hp. b. Hin tng quang in trong Hin tng nh sng gii phng cc electron lin kt chng tr thnh cc electron dn ng thi to ra cc l trng cng tham gia vo qu trnh dn in, gi l hin tng quang in trong. c. Quang in tr c ch to da trn hiu ng quang in trong. l mt tm bn dn c gi tr in tr thay i khi cng chm nh sng chiu vo n thch hp. d. Pin quang in Pin quang in l ngun in trong quang nng c bin i trc tip thnh in nng. Hot ng ca pin da trn hin tng quang in trong ca mt s cht bn dn ( ng xit, slen, silic,...). Sut in ng ca pin thng c gi tr t 0,5 V n 0,8 V Pin quang in (pin mt tri) tr thnh ngun cung cp in cho cc vng su vng xa, trn cc v tinh nhn to, con tu v tr, trong cc my o nh sng, my tnh b ti.

III. So snh hin tng quang in ngoi v quang in trong: So snh Hin tng quang in ngoi Hin tng quang dn

Vt liu Kim loi Cht bn dn

Bc sng as kch thch Nh, nng lng ln (nh tia t ngoi) Va, nng lng trung bnh (as nhn thy..)

Do u im ch cn as kch thch c nng lng nh (bc sng di nh as nhn thy) nn hin tng quang in trong c ng dng trong quang in tr (in tr thay i khi chiu as kch thch, dng trong cc mch iu khin t ng) v pin quang in (bin trc tip quang nng thnh in nng)

IV. Hin tng quangPht quang. a. S pht quang + C mt s cht khi hp th nng lng di mt dng no , th c kh nng pht ra cc bc x in t trong min nh sng nhn thy. Cc hin tng gi l s pht quang. + Mi cht pht quang c mt quang ph c trng cho n. b.Hunh quang v ln quang- So snh hin tng hunh quang v ln quang:

So snh Hin tng hunh quang Hin tng ln quang

Vt liu pht quang Cht kh hoc cht lng Cht rn

Thi gian pht quang Rt ngn, tt rt nhanh sau khi tt as kch thch

Ko di mt khong thi gian sau khi tt as kch thch (vi phn ngn giy n vi gi, ty cht)

c im - ng dng As hunh quang lun c bc sng di hn as kch thch (nng lng nh hn- tn s ngn hn)

Bin bo giao thng, n ng

c. nh lut Xtc v s pht quang( c im ca nh sng hunh quang ) nh sng pht quang c bc sng hq di hn bc sng ca nh sng kch thch kt:

hf hq < hfkt => hq > kt. d.ng dng ca hin tng pht quang S dng trong cc n ng thp sng, trong cc mn hnh ca dao ng k in t, tivi, my tnh. S dng sn pht quang qut trn cc bin bo giao thng.

V. Mu nguyn t Bo. a. Mu nguyn t ca Bo +Tin v trng thi dng -Nguyn t ch tn ti trong mt s trng thi c nng lng xc nh En, gi l cc trng thi dng. Khi trng thi dng, nguyn t khng bc x.

Welcome PCStamp


-Trong cc trng thi dng ca nguyn t, electron chuyn ng quanh ht nhn trn nhng qu o c bn knh hon ton xc nh gi l qu o dng. -Cng thc tnh qu o dng ca electron trong nguyn t hyr: rn = n2r0, vi n l s nguyn v r0 = 5,3.10-11 m, gi l bn knh Bo (lc e qu o K)

Trng thi dng n 1 2 3 4 5 6

Tn qu o dng K L M N O P

Bn knh: rn = n2r0 r0 4r0 9r0 16r0 25r0 36r0

Nng lng e Hidro 2

13,6( )nE eV

n= -

2

13,6

1-

2

13,6

2-

2

13,6

3-

2

13,6

4-

2

13,6

5-

2

13,6

6-

Nng lng electron trong nguyn t hir: 2

13,6( )nE eV

n= - Vi n N*.

-Bnh thng, nguyn t trng thi dng c nng lng thp nht gi l trng thi c bn. Khi hp th nng lng th nguyn t chuyn ln trng thi dng c nng lng cao hn, gi l trng thi kch thch. Thi gian nguyn t trng thi kch thch rt ngn (c 10-8 s). Sau nguyn t chuyn v trng thi dng c nng lng thp hn v cui cng v trng thi c bn. + Tin v s bc x v hp th nng lng ca nguyn t -Khi nguyn t chuyn t trng thi dng c nng lng En sang trng thi dng c nng lng Em nh hn th

nguyn t pht ra mt phtn c nng lng: = hfnm = En Em.

-Ngc li, nu nguyn t trng thi dng c nng lng Em m hp th c mt phtn c nng lng hf ng bng hiu En Em th n chuyn sang trng thi dng c nng lng En ln hn. -S chuyn t trng thi dng Em sang trng thi dng En ng vi s nhy ca electron t qu o dng c bn knh rm sang qu o dng c bn knh rn v ngc li.

b. Quang ph pht x v hp th ca nguyn t hidr -Nguyn t hir c cc trng thi dng khc nhau EK, EL, EM, ... . Khi electron chuyn ng trn cc qu o dng K, L, M, ... -Khi electron chuyn t mc nng lng cao (Ecao) xung mc

nng lng thp hn (Ethp) th n pht ra mt phtn c nng lng xc nh: hf = Ecao Ethp.

-Mi phtn c tn s f ng vi mt sng nh sng n sc c bc sng =f

c, tc l mt vch quang ph c mt

mu (hay mt v tr) nht nh. iu l gii quang ph pht x ca hir l quang ph vch. -Ngc li nu mt nguyn t hir ang mt mc nng lng Ethp no m nm trong mt chm nh sng trng, trong c tt c cc phtn c nng lng t ln n nh khc nhau, th lp tc nguyn t s hp th mt phtn

c nng lng ph hp = Ecao Ethp chuyn ln mc nng lng Ecao. Nh vy, mt sng nh sng n sc b hp th, lm cho trn quang ph lin tc xut hin mt vch ti. Do quang ph hp th ca nguyn t hir cng l quang ph vch.

VI. S lc v laze. Laze l mt ngun sng pht ra mt chm sng cng ln da trn vic ng dng hin tng pht x cm ng. a.. c im ca laze + Laze c tnh n sc rt cao. + Tia laze l chm sng kt hp (cc phtn trong chm c cng tn s v cng pha). + Tia laze l chm sng song song (c tnh nh hng cao). + Tia laze c cng ln. V d: laze rubi (hng ngc) c cng ti 106 W/cm2. b. Mt s ng dng ca laze + Tia laze c dng nh dao m trong phu thut mt, cha mt s bnh ngoi da (nh tc dng nhit), . + Tia laze dng truyn thng thng tin bng cp quang, v tuyn nh v, iu khin con tu v tr, ... + Tia laze dng trong cc u c a CD, bt ch bng, bn , th nghim quang hc trng ph thng, ... + Tia laze c dng trong o c , ngm ng thng ... + Ngoi ra tia laze cn c dng khoan, ct, ti, ...chnh xc cc vt liu trong cng nghip.

hp th bc x

hfmn

En

Em

hfnm


B. CC DNG BI TP I. HIN TNG QUANG IN: 1. Cc cng thc:

+Nng lng ca phtn nh sng: = hf . Trong chn khng: =

hc.

+Cng thc Anhxtanh: hf =

hc= A +

2

1mv 2 max0 =

0

hc + Wdmax;

+Gii hn quang in : 0 = A

hc;

+ Cng thot ca e ra khi kim loi : 0

.

chA

v0Max l vn tc ban u ca electron quang in khi thot khi catt

f, l tn s, bc sng ca nh sng kch thch

+ dng quang in trit tiu th UAK Uh (Uh < 0): 2

0 ax

2

Mh

mveU = Uh gi l hiu in th hm

Lu : Trong mt s bi ton ngi ta ly Uh > 0 th l ln. + Xt vt c lp v in, c in th cc i VMax v khong cch cc i dMax m electron chuyn ng

trong in trng cn c cng E c tnh theo cng thc: 2

ax 0 ax ax

1

2M M Me V mv e Ed= =

+ Vi U l hiu in th gia anot v catot, vA l vn tc cc i ca electron khi p vo ant, vK = v0Max l

vn tc ban u cc i ca electron khi ri catt th: 2 21 1

2 2A Ke U mv mv= -

+S ht photn p vo: pt pt

N = = hc

+Cng sut ca ngun sng: nP

n l s photon pht ra trong mi giy. l lng t nh sng.

+Cng dng quang in bo ha: enI ebh (Gi s n= ne , vi n l s electron n c Ant)

en l s quang electron bc ra khi catot mi giy = n s electron ti anot mi giy

e l in tch nguyn t.

+Hiu in th hm: 2

0

1/ /

2h eeU m v

+Hiu sut lng t: n

nH e Hay : bh

I hcH =

p e

en l s electron bc ra khi catot kim loi mi giy. n l s photon p vo catot trong mi giy.

2. Cc HNG S Vt L v I N V Vt L : +Hng s Plank: h = 6,625.10-34 J.s +Vn tc nh sng trong chn khng: c = 3.108 m/s +in tch nguyn t : |e| = 1,6.10-19 C; hay e = 1,6.10-19 C +Khi lng ca e : m (hay me ) = 9,1.10-31 kg +i n v: 1eV=1,6.10-19J. 1MeV=1,6.10-13J. +Cc hng s c ci sn trong my tinh cm tay Fx570MS; Fx570ES; 570ES Plus bng cc lnh:

[CONST] Number [0 40] ( xem cc m lnh trn np ca my tnh cm tay ) . +Lu : Khi tnh ton dng my tnh cm tay, ty theo yu cu bi c th nhp trc tip cc hng s t bi cho , hoc nu mun kt qu chnh xc hn th nn nhp cc hng s thng qua cc m lnh CONST

[0 40] c ci t sn trong my tinh! (Xem thm bng HNG S VT L di y)


* -V d1: My 570ES:

Cc hng s Thao tc bm my Fx 570ES Kt qu hin th mn hnh Ghi ch Hng s Plng (h) SHIFT 7 CONST 06 = 6.62606876 .10-34 J.s

Tc nh sng trong chn khng (C0) hay c

SHIFT 7 CONST 28 = 299792458 m/s

in tch lectron (e) SHIFT 7 CONST 23 = 1.602176462 10-19 C

Khi lng lectron (me) SHIFT 7 CONST 03 = 9.10938188 .10-31 Kg

Hng s Rydberg RH (R) SHIFT 7 CONST 16 = 1,097373157.10 7 (m-1)

3. Cc dng bi tp: Cho 1 eV = 1,6.10-19 J ; h = 6,625.10-34 Js ; c = 3.108 m/s; me = 9,1.10-31 kg. Dng 1: Tnh gii hn quang in, cng thot v vn tc cc i ban u ca e quang in khi bt ra khi Katot.

a.PPG: -Gii hn quang in: 0 = A

hc ; Cng thot

0

.

chA ; A: J hoc eV; 1eV =1,6.10-19 J

-Phng trnh Anhxtanh:hf =

hc= A +

2

1mv 2max0

-ng nng cc i: max0

1 1( )dW hc

2

0

0

1

2

hc hcmv

=> 0

0

2 1 1( )

e

hcv

m

-Cc hng s : 34 8 196,625.10 ; 3.10 / ; 1,6.10h c m s e C ; 319,1.10em kg

b.Cc V d :

V d 1: Gii hn quang in ca km l o = 0,35m. Tnh cng thot ca lectron khi km?

HD gii: T cng thc: 0

hc hcA

0 A

34 86,625.10 .3.10

60,35.10

=5,67857.10-19 J =3,549eV

Bm my tnh: phn s SHIFT 7 06 h X SHIFT 7 28 Co 0,35 X10x -6 = 5.6755584x10-19J

i sang eV: Chia tip cho e: Bm chia SHIFT 7 23 = Hin th: 3,5424 eV

Nhn xt: Hai kt qu trn khc nhau l do thao tc cch nhp cc hng s !!!

V d 2: (TN-2008): Gii hn quang in ca ng (Cu) l 0 = 0,30 m. Bit hng s h = 6,625.10-34 J.s v vn tc truyn nh sng trong chn khng c = 3.108 m/s. Cng thot ca lectrn khi b mt ca ng l

A.6,625.10-19 J. B. 6,265.10-19 J. C. 8,526.10-19 J. D. 8,625.10-19 J.

HD Gii: Cng thot: .J 6,625.1010.3,0

10.3.10.625,6 19-6

834

0

hcA p n A

V d 3: Gi hn quang in ca Ge l o = 1,88m. Tnh nng lng kch hat (nng lng cn thit gii phng mt lectron lin kt thnh lectron dn) ca Ge?

HD gii: T cng thc: 0

hc hcA

0 A

34 86,625.10 .3.10

61,88.10

=1,057.10-19 J = 0,66eV

V d 4: Mt kim loi c cng thot l 2,5eV. Tnh gii hn quang in ca kim loi : A. 0,4969 m B. 0,649 m C. 0,325 m D. 0,229 m

HD Gii: Gii hn quang in 34 8

19

hc 6.625.10 .3.100 A 2.5.1,6.10

=4,96875.10-7 m = 0,4969m .p n A

V d 5: Gii hn quang in ca KL dng lm Kotot l 0,66m. Tnh: 1. Cng thot ca KL dng lm K theo n v J v eV. 2. Tnh ng nng cc i ban u v vn tc cc i ca e quang in khi bt ra khi K, bit nh sng

chiu vo c bc sng l 0,5m .

HD gii: 1.0

hc hcA

0 A

=1,875eV=3.10-19 J .


2. max0

1 1(dW hc

) = 9,63.10-20 J => 00

2 1 1( )

e

hcv

m

Th s:

34 8

0 31 6

2.6,625.10 .3.10 1 1( )

9,1.10 .10 0,5 0,66v

= 460204,5326 = 4,6.105 m/s

V d 6: Catt ca mt t bo quang in c cng thot bng 3,5eV. a. Tm tn s gii hn v gii hn quang in ca kim loi y. b. Khi chiu vo catt mt bc x c bc sng 250 nm c xy ra hin tng quang in khng? -Tm hiu in th gia A v K dng quang in bng 0. -Tm ng nng ban u cc i ca cc lectron quang in. -Tm vn tc ca cc lectron quang in khi bt ra khi K.

HD gii:

a.Tn s gii hn quang in: f = c/0 = A/h = 3,5.1,6.10-19/6,625.10-34 = 0,845.1015 Hz.

Gii hn quang in o = hc/A = 6,625.10-34.3.108/3,5.1,6.10-19= 3,55.10-7m. =0,355 m

b. V = 250 nm =0,250m < o = 0,355 m nn xy ra hin tng quang in - dng quang in trit tiu th cng ca in trng phi trit tiu ng nng ban u cc i ca lectron quang.

2 2 34 8190 0

19 8

1 1 6,625.10 .3.10( ) ( 3,5.1,6.10 )

2 2. 1,6.10 25.10h h

mv mv hceU U A

e e

=> Uh = - 1,47 V

-ng nng ban u cc i 2

0 / / 1,472

h

mveU eV = 1,47.1,6.10-19 = 2,35.10-19J = 0,235.10-18J

Hay : W =

88

834

0

2

0

10.5,35

1

10.25

110.3.10.625,6

11hc

2

mv= 0,235.10-18J

-Vn tc ca lectron 5

31

18

0 10.19,710.1,9

10.235,0.22

m

Wv m/s.

Dng 2: Lin h gia ng nng ban u( vn tc ban u)v hiu in th hm gia 2 cc ca A v K trit tiu dng quang in.

PPG. -PT Anhxtanh: hf =

hc= A +

2

1mv 2max0 .

- nh l ng nng: max. deUh W => 0

1 1( )h

hcU

e

V d 1: Ta chiu nh sng c bc sng0,42 m vo K ca mt tbq. Cng thot ca KL lm K l 2eV. trit tiu dng quang in th phi duy tr mt hiu in th hmUAK bng bao nhiu?

HD Gii: 0

1 1( )h

hcU

e Tnh c Uh= - 0,95V

V d 2: Chiu chm bc x in t c tn s f = 5,76.1014 Hz vo mt ming kim loi th cc quang electron c vn tc ban u cc i l v = 0,4.106 m/s. Tnh cng thot electron v bc sng gii hn quang in ca kim loi .

HD Gii : A = hf - 202

1mv = 3,088.10-19 J; 0 =

A

hc= 0,64.10-6 m.

V d 3: Cng thot electron khi kim loi natri l 2,48 eV. Mt t bo quang in c catt lm bng natri,

khi c chiu sng bng chm bc x c = 0,36 m th cho mt dng quang in c cng bo ha l

3A. Tnh vn tc ban u cc i ca electron quang in v s electron bt ra khi catt trong 1 giy.

HD Gii: Wd0 =

hc- A = 1,55.10-19 J; v0 =

m

Wd 02 = 0,58.106 m/s; ne = e

Ibh = 1,875.1013.

V d 4: Chiu bc x c bc sng = 0,438 m vo catt ca mt t bo quang in. Bit kim loi lm

catt ca t bo quang in c gii hn quang in l 0 = 0,62 m. Tm in p hm lm trit tiu dng quang in.


HD Gii : Wd0 =

hc-

0

hc= 1,33.10-19 J; Uh = -

e

Wd 0 = - 0,83 V.

V d 5: Chiu mt bc x in t c bc sng vo catt ca mt t bo quang in. Bit cng thot electron ca kim loi lm catt l 3eV v cc electron bn ra vi vn tc ban u cc i l 7.105 m/s. Xc nh bc sng ca bc x in t v cho bit bc x in t thuc vng no trong thang sng in t.

HD Gii : = 2

02

1mvA

hc

= 0,215.10-6 m; bc x thuc vng t ngoi.

V d 6: Chiu bc x c bc sng 0,405m vo mt tm kim loi th cc quang electron c vn tc ban u cc i l v1. Thay bc x khc c tn s 16.1014 Hz th vn tc ban u cc i ca cc quang electron l v2 = 2v1. Tm cng thot electron ca kim loi.

HD Gii: f1 = 1

c= 7,4.1014 Hz; 21

2

1mv = hf1 A;

2

22

1mv = 4 21

2

1mv = hf2 A

4 = Ahf

Ahf

1

2 A = 3

4 21 hfhf = 3.10-19 J.

V d 7: Chiu bc x c bc sng = 0,4 m vo catt ca mt t bo quang in. Bit cng thot electron ca kim loi lm catt l A = 2 eV, in p gia ant v catt l UAK = 5 V. Tnh ng nng cc i ca cc quang electron khi ti ant.

HD Gii : W0 =

hc- A = 8,17.10-19 J; Wmax = W0 + |e|UAK = 16,17.10

-19 J = 10,1 eV.

V d 8: Catot ca t bo quang in lm bng ng, cng thot khi ng l 4,47eV. Cho bit: h = 6,625.10-34 (J.s) ; c = 3.108 (m/s) ; e = 1,6.10-19 (C). a. Tnh gii hn quang in ca ng. b. Chiu ng thi 2 bc x in t c bc sng 1 = 0,210 (m) v 2 = 0,320 (m) vo catot ca t bo quang in trn, phi t hiu th hm bng bao nhiu trit tiu hon ton dng quang in. HD Gii :

a. Tnh 0 .Gii hn quang in ca ng: 0 = (278,010.6,1.47,4

10.3.10.625,619

834

A

hcm).

b. Tnh Uh: 1 < 0 < 2 do ch c 1 gy ra hin tng quang in.

iu kin dng quang in trit tiu: maxhAK WeUUe . )(446,11max VA

hc

ee

WU h

V d 9: Tnh nng lng, ng lng v khi lng ca photn ng vi cc bc x in t sau y: a. Bc x c = 0,76 m. b. Sng v tuyn c = 500 m. c. Tia phng x c f = 4.1017 KHz. Cho bit c = 3.108 m/s ; h = 6,625.10-34 J.s HD Gii : a. Bc x c = 0,76 m.

- Nng lng: = hf = )(10.15,2610.76,0

10.3.10.625,6 206

834

J

- ng lng: = )/.(10.72,8 28 smkgc

. - Khi lng: m = 2c

= 2,9.10-36 (kg).

b. Sng v tuyn c = 500 m. Tng t, ta c: - Nng lng: = hf = )(10.975,3 28 J

- ng lng: = )/.(10.325,1 36 smkgc

. - Khi lng: m = 2c

= 4,42.10-45 (kg).

c. Tng t:- Nng lng: = hf = 26,5.10-14 (J).

- ng lng: = )/.(10.8,8 22 smkgc

. - Khi lng: m = 2c

= 0,94.10-31 (kg).

Dng 3: Cho UAK> 0 hy tnh vn tc ca e khi p vo Anot. PPG: Gi v l vn tc ca e khi p vo Anot. p dng nh l ng nng:


2 2

0

1 1

2 2AKmv mv eU =>

2 2

0

1 1

2 2AKmv mv eU =>

21

2AKmv A eU

2

0

1 1 1( )

2AKmv hc eU

=> v ....

Dng 4: Cho cng sut ca ngun bc x. Tnh s Phton p vo Katot sau thi gian t PPG: Nng lng ca chm photon ri vo Katot sau khong thi gian t: W = P.t

-S photon p vo Katot: . .

.

W P tn

h c

-Cng sut ca ngun : P = n.. (n l s photon tng ng vi bc x pht ra trong 1 giy). -Cng dng in bo ho : Ibh = ne.e .(ne l s electron quang in t catot n anot trong 1 giy).

-Hiu sut quang in : H = n

ne

V d 1: Mt ngn n pht ra nh sng n sc c =0,6m s pht ra bao nhiu photon trong 10s nu cng

sut n l P = 10W.Gii:

620

34 8

. . 10.0,6.10 .103,0189.10

. 6.625.10 .3.10

W P tn

h c

= 3,02 .1020 photon

V d 2: Ngun Laser mnh pht ra nhng xung bc x c nng lng 3000W J . Bc x pht ra c bc sng nm480 . Tnh s photon trong mi bc x ?

HD Gii : Gi s photon trong mi xung l n .( l nng lng ca mt photon)

Nng lng ca mi xung Laser: W n 9

21

34 8

. 3000.480.107,25.10

. 6,625.10 .3.10

W Wn

h c

photon

Dng 5: Cho cng dng quang in bo ho. Tnh s e quang in bt ra khi Katot sau khong thi gian t.

PPG: in lng chuyn t K A : q= Ibh.t = ne.e => .bh

e

I tqn

e e

Gi ne l s e quang in bt ra Kaot ( ne n );

Gi n l s e quang n c Ant ( n ne , Khi I = Ibh. Th n = ne )

Lu : Nu khng cho r % e quang in bt ra v c Anot th lc ta c th cho n= ne = n

V d 1: Cho cng dng quang in bo bo l 0,32mA. Tnh s e tch ra khi Katot ca t bo quang in trong thi gian 20s bit ch 80% s e tch ra v c Anot.

HD Gii: H =n

ne= 0,8 => n =

en

H Hay:

.

.bhI tn

e H .Th s:

316

19

0,32.10 .205.10

1,6.10 .0,8n hat

V d 2: Mt t bo quang in c catt lm bng Asen c cng thot electron bng 5,15 eV. Chiu chm

sng n sc c bc sng 0,20 m vo catt ca t bo quang in th thy cng dng quang in bo

ha l 4,5 A. Bit cng sut chm bc x l 3 mW . Xc nh vn tc cc i ca electron khi n va b bt ra khi catt v hiu sut lng t.

HD Gii . Ta c: Wd0 =

hc- A = 1,7.10-19 J; v0 =

m

Wd 02 = 0,6.106 m/s.

ne = e

Ibh = 2,8.1013; n = hc

P

hc

P

= 3.1015 H = n

ne = 9,3.10-3 = 0,93%.

Dng 6: Tnh hiu sut lng t ca t bo quang in. PPG: Hiu sut lng t ca t bo quang in l i lng c tnh bng t s gia s e quang in bt ra khi Katot vi s photon p vo Katot.


H = n

ne =>

.

.

. .

bh

bh

I tI hceH

P t e Phc

.

V d 1: Khi chiu 1 bc x in t c bc sng 0,5 micromet vo b mt ca t bo quang in to ra dng in bo ha l 0,32A. Cng sut bc x p vo Katot l P=1,5W. tnh hiu sut ca t bo quang in.

HD Gii:

34 8

19 6

. . 0,32.6,625.10 .3.10.100% 53%

. . 1,6.10 .1,5.0,5.10bhI h cHe P

V d 2: Kim loi lm catot ca t bo quang in c gii hn quang in 0,32 (m). Chiu nh sng c bc sng 0,25 (m) vo catot ca t bo quang in trn. Cho bit : h = 6,625.10-34 (J.s) ; c = 3.108 (m/s) ; me = 9,1.10-31 (kg) ; -e = -1,6.10-19 (C). a) Tnh vn tc ban u cc i ca electron quang in. b) Bit rng cc electron thot ra u b ht v anot, cng dng quang in bo ho bng 0,7 mA. Tnh s electron thot ra khi catot trong mi giy.

HD Gii: Ta c: 2max02

1mvUe AK .

Phng trnh Anh-xtanh :

hc =

2

2

max0mvA = A + eUh .

Theo iu kin bi ton, ta c: sJc

UUeh

eUAhc

eUAhc

hh

h

h

.10.433,611

)( 34

12

12

2

2

1

1

.

V d 3: Cng thot ca lectron i vi Natri l 2,48 (eV). Catot ca t bo quang in lm bng Natri c chiu sng bi bc x c bc sng = 0,36 (m) th c dng quang in bo ho Ibh = 50 (mA).Cho bit:h = 6,625.10-34 (J.s); c = 3.10 (m/s) ; me = 9,1.10

-31 (kg); - e = - 1,6.10-19 (C).

a) Tnh gii hn quang in ca Natri. b) Tnh vn tc ban u cc i ca lectron quang in. c) Hiu sut quang in bng 60%, tnh cng sut ca ngun bc x chiu vo catt. HD Gii:

a) Tnh 0. Gii hn quang in : 0 = (5,0A

hcm).

b) Tnh v0. Phng trnh Anh-xtanh:

hc =

2

2

max0mvA .

Suy ra: smAhc

mv

e

/10.84,52 5

max0

c) Tnh P. Ta c Ibh = ne.e suy ra ne = e

Ibh . P = n. suy ra n =

P.

n

nH e do 29,0

.

He

hcIP bh (W).

Dng 7: ng dng ca hin tng quang in tnh cc hng s h, e, A. p dng cc cng thc:

- Nng lng ca phtn : = hf = h

c.

- Phng trnh Anh-xtanh : = 2

2

max0mvA .

- Hiu in th hm : 2max02

1mveUUe hAK .


V d 1: Khi chiu mt chm sng vo mt kim loi th c hin tng quang in xy ra. Nu dng hiu in th hm bng 3 (V) th cc lectron quang in b gi li khng bay sang anot c. Cho bit gii hn quang in ca kim loi l : 0 = 0,5 (m) ; h = 6,625.10-34 (J.s) ; c = 3.108 (m/s) ; -e = -1,6.10-19 (C). Tnh tn s ca chm nh sng ti kim loi.

HD Gii :Cc lectron quang in b gi li hon ton khng qua c anot nn : 2max02

1mveUUe hAK

Phng trnh Anh-xtanh : hf = A + 2max02

1mv .

Hay hf = eUh + A = eUh + 0

hc ; Suy ra: f =

0

c

h

eU h .

Thay s, ta c : )(10.245,1310.5,0

10.3

10.625,6

3.10.6,1 146

8

34

19

Hzf

.

V d 2: Chiu bc x c bc sng 0,35 (m) vo mt kim loi, cc lectron kim quang in bn ra u b gi li bi mt hiu in th hm. Khi thay chm bc x c bc sng gim 0,05 (m) th hiu in th hm tng 0,59 (V). Tnh in tch ca lectron quang in. Cho bit : h = 6,625.10-34 (J.s) ; c = 3.108 (m/s).

HD Gii :Ta c

hc =

2

2

max0mvA = A + eUh ( Phng trnh Anh-xtanh)

Theo iu kin bi ton:

)( UUeAhc

eUAhc

h

h

Vi U = 0,59 (V) v = 0,05 (m). Suy ra: )(10.604,111 19 C

U

hce

.

V d 3: Ln lt chiu hai bc x c bc sng 1 = 0,405 (m), 2 = 0,436 (m) vo b mt ca mt kim loi v o hiu in th hm tng ng Uh1 = 1,15 (V); Uh2 = 0,93 (V). Cho bit: h = 6,625.10-34 (J.s) ; c = 3.108 (m/s) ; e = 1,6.10-19 (C). Tnh cng thot ca kim loi . HD Gii :

Ta c:

hc =

2

2

max0mvA = A + eUh ( Phng trnh Anh-xtanh)

Theo iu kin bi ton:

)( UUeAhc

eUAhc

h

h

Suy ra : )(92,111

2

121

21

eVUUehcA hh

.

Dng 8: Chiu nh sng kch thch c bc sng thch hp vo b mt tm KL (hay qu cu) c c lp v in. Tnh hiu in th cc i m tm KL t c. PPG: Khi chiu nh sng kch thch vo b mt KL th e quang in b bt ra, tm KL mt in t (-) nn tch in (+) v c in th l V. in trng do in th V gy ra sinh ra 1 cng cn AC = e.V ngn cn s bt ra ca cc e tip theo. Nhng ban u AC < Wdmax , nn e quang in vn b bt ra. in tch (+) ca tm KL tng dn, in th V tng dn. Khi V =Vmax th cng lc cn c ln ng bng Wdmax ca e quang in nn e khng cn bt ra.

Ta c: 2

ax 0max

1

2M eeV m v => ax

0

M

hc hceV A

Vy ax

0

1 1( )M

hcV

e

V d 1: Mt qu cu bng ng (Cu) c lp v in c chiu bi 1 bc x in t c = 0,14 (m), . Cho gii hn quang in ca Cu l 1 = 0,3 (m). Tnh in th cc i ca qu cu.

HD Gii:

34 8

ax 19 6 6

0

1 1 6,625.10 .3.10 1 1( ) ( ) 4,73

1,6.10 0,14.10 0,3.10M

hcV V

e

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