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HIN TNG QUANG I

1. Th nghim ca Hc x v hi

a) Th nghim:

*Chiu nh sng pht ra t

l km tch in m, gn trn m

thy 2 l ca in nghim c

b mt in tch m.

*Thay l km tch in m b

dng th hin tng ny khng x

*Dng mt tm thy tinh

quang (ta bit thy tinh h

th hin tng cng khng x

*Thay tm km tch in m b

m th hin tng cng xy ra tng t

b) Gii thch:

*Kt qu th nghim trn ch

quang vo l km (hoc cc kim lo

gi hin tng ny l hin t

*Trong trng hp l k

nhng hu ht cc electron b

km khng thay i.

*Trong trng hp chn chm sng h

in khng xy ra chng t v

ngoi.

c) Kt lun:

luyenthihanoi.com.vn

D

Luy

Gia s t

/c: S

N TNG QUANG IN NGOI

hin tng quang in (nm 1887)

u nh sng pht ra t mt h quang in vo

n trn mt in nghim th

p li, chng t l km

n m bng l km tch in

ng ny khng xy ra.

y tinh chn chm sng h

p th mnh tia t ngoi)

y ra.

n m bng cc kim loi nh ng, bc khc c

y ra tng t.

m trn ch gii thch c nu nh cng nhn khi chi

c cc kim loi khc) lm bt cc electron ra kh

n tng quang in.

m tch in dng th hin tng quang i

t cc electron bt ra u b l km ht tr li ngay lm cho i

n chm sng h quang bng tm thy tinh th hi

vi l km, hin tng quang in ch

Trung tm Thy Hong

Dy nhm cht lng cao ton l ha ti

Luyn thi vo lp 10, luyn thi quc gia THPT

Gia s ti nh cc mn vn ha cho hc sinh c

/c: S 8A ngch 69B ng 121 Kim Ngu

0974 222 456

N NGOI

c khc cng tch in

n khi chiu nh sng h

t cc electron ra khi kim loi. Hc x

ng quang in vn xy ra

i ngay lm cho in tch ca l

y tinh th hin tng quang

xy ra vi nh sng t

C Nh

ting anh lp 10, 11, 12

c gia THPT

c sinh cp 2, cp 3

HBT HN


Hin tng quang in ngoi (g

sng lm bt electron ra khi kim lo

Cc electron bt ra gi l cc electron quang i

t)

2. Th nghim vi t bo quang i

a) Cu to:

T bo quang in l mt bnh c

Anot A: thng l mt vng dy kim lo

Katot K: thng l mt ch

quang in.

b) Th nghim:

B tr th nghim nh hnh v

c tc dng lm thay i hi

anot v katot.

*Khi cha chiu nh sng vo katot th

kim ca mili ampe k ch s

*Chiu sng katot bng cc nh sng

n sc c bc sng khc nhau th th

khi bc sng nh sng nh

no kim ca mili ampe k

tr s 0, tc l c dng i

Dng in ny gi l dng qu

*Tng dn hiu in th

katot (UAK) th cng dng quang

tng. Nhng khi UAK tng

no , tip tc tng UAK th c

quang in khng tng n

c gi l cng dng quang

ha (Ibh).

*Tng cng chm sng th th

n ngoi (gi tt l hin tng quang i

i kim loi.

i l cc electron quang in (hay cc quang electron, quang i

bo quang in

t bnh cu bng thch anh, chn khng. Bn trong c hai i

t vng dy kim loi

t chm cu lm bng kim loi dng

nh v. Bin tr R

u in th gia

u nh sng vo katot th

0.

ng cc nh sng

c sng khc nhau th thy

hn mt gi tr

a mili ampe k lch khi v

n trong mch.

i l dng quang in.

gia anot v

dng quang in

tng n mt gi tr

th cng dng

a, gi tr ny

dng quang in bo

chm sng th thy cng dng quang in bo ha c

Ibh1

Iq

-Uh

Ibh2

ng c trng vn ca t bo quang i

n): l hin tng nh

c quang electron, quang in

ch anh, chn khng. Bn trong c hai in cc

i dng kho st hin tng

n bo ha cng tng.

UAK

c trng vn ampe bo quang in


*Di chuyn con chy C sang na bin tr bn phi hiu in th UAK mang gi tr

m th thy khi UAK -Uh th dng quang in b trit tiu (Iq = 0). Uh c gi l ln

hiu in th hm.

c) Gii thch:

*khi chiu vo katot nh sang thch hp th c hin tng quang in xy ra v cc

electron quang in bt ra khi katot. Di tc dng ca in trng hng t anot sang

katot, cc electron ny chuyn ng v pha anot to thanh dng quang in.

*Tng hiu in th UAK th s electron i v anot tng, tc l cng dng quang

in tng.

*Khi tng UAK n mt gi tr no th tt c cc electron quang in bt ra khi

katot u i c v anot nn nu tip tc tng UAK th cng dng quang in

khng tng na.

*Khi UAK -Uh th hin tng quang in vn xy ra nhng tt c cc electron quang

in bt ra katot u khng i c n anot (do chu tc dng ca in trng cn)

nn khng to thnh dng quang in.

3. Ba nh lut quang in

T kt qu th nghim vi t bo quang in, ngi ta rt ra 3 nh lut quang in

nh lut 1:

Mi kim loi dng lm catot c mt bc sng gii hn 0 xc nh gi l gii hn quang

in. Hin tng quang in ch xy khi bc sng ca nh sng kch thch nh hn hoc

bng gii hn quang in.

Ch :

-iu kin xy ra hin tng quang in: 0

-T iu kin xy ra hin tng quang in, suy ra nh ngha gii hn quang in: l

bc sng ln nht c th gy ra c hin tng quang in i vi kim loi.

nh lut 2:

i vi cc nh sng tha mn nh lut quang in 1 th cng dng quang in

bo ha t l vi cng ca chm sang kch thch.

nh lut 3:


ng nng ban u cc ca cc electron quang in khng ph thuc vo cng ca

chm sng kch thch m ch ph thuc vo bc sng ca nh sng kch thch v bn cht

kim loi dung lm katot.

4. Thuyt lng t

Dng thuyt sng nh sng khng gii thch c 3 nh lut quang in.

khc phc b tc ny, nm 1900 Max Pank a ra gi thuyt gi l gi thuyt Pank:

Nguyn t hay phn t khng hp th hay bc x nh sng mt cch lin tc m thnh

tng phn ring l, mi phn mang mt nng lng = hf

Vi gi l lng t nng lng (n v: J)

f l tn s ca nh sng

h = 6,625.10-34 (J.s) gi l hng s Plank

Nm 1905, Anbert Einstein m rng gi thuyt ca Plank thnh thuyt lng t nh sng

gm cc ni dung sau:

-Chm sng ging nh mt chm ht. Mi ht gi l 1 photon.

-Khi nh sng truyn i, cc photon bay dc theo chiu truyn ca tia sng.

-Vi mi nh sng n sc c tn s f, cc photon u c nng lng nh nhau bng =

hf. Khi nh sng truyn i, nng lng ca cc photon khng thay i, khng ph thuc vo

khong cch n ngun sng.

-Photon ch tn ti trng thi chuyn ng. Trong chn khng, photon bay vi tc c

= 3.108 m/s.

-Nguyn t, phn t hp th hay bc x nh sng cng c ngha l hp th hay bc x

photon. Mi ln mt nguyn t (phn t) pht x hay hp th nh sng th chng ch pht ra

hay hp th 1 photon.

-Khi xy ra hiu ng quang in, nguyn t hp th 1 photon lm gii phng ra 1

electron. Nng lng photon c dng vo lm 2 vic:

*Th nht, cung cp cho electron mt nng lng thot ra khi nguyn t (nng

lng gi l cng thot)

*Th hai, cung cp cho electron mt ng nng ban u n bay i. i vi cc

electron lp ngoi cng th ng nng ny c gi tr cc i.

= A + W0max


Ch : Dng thuyt lng t, ta c th gii thch c 3 nh lut quang in.

5. Cc cng thc cn nh gii ton

*Nng lng lng t (nng lng 1 photon)

= hf = hc

Trong : l nng lng 1 photon (n v: J)

f l tn s ca nh sng (n v: Hz)

l bc sng ca nh sng trong chn khng (m)

h l hng s Plank, h = 6,625.10-34 (J.s)

c l tc nh sng trong chn khng, c = 3.108 (m/s)

*Cng thot (nng lng cn thit bt 1 electron ra khi nguyn t)

A = hf0 = 0

hc

Vi f0 l tn s gii hn quang in; 0 l bc sng gii hn quang in

Ch :

-i n v:

, 0 thng c n v m, phi i v m: 1 m = 10-6 m.

, A ngoi n v chun l J, ngi ta cn hay dng n v eV: 1 eV = 1,6.10-19 J

-iu kin hin tng quang in xy ra: f f0 hay 0

*Cng thc Anhxtanh v hin tng quang in:

= A + W0max

Vi = hf = hc

; A = hf0 =

0

hc

; W0max =

2

0maxm.v

2

Suy ra: 2

0max

0

hc hc mv = +

2

*Ch :


-Khi nh sng i t mi trng ny sang mi trng khc th nng lng ca cc

photon khng thay i.

-Hp kim l hn hp ca nhiu kim loi c gii hn quang in khc nhau th gii hn

quang in ca hp kim l gii hn quang in ln nht.

-Nu chm sng chiu vo kim loi (chm sng kch thch) gm nhiu nh sng n

sc u c th gy ra hiu ng quang in vi kim loi th khi tnh ton ta ch ly nh

sng c tn s ln nht hay bc sng nh nht.

6. Bi tp vn dng

Cu 1. Cng thot lectron ra khi mt kim loi A = 6,625.10-19J. Cho hng s Plng h = 6,625.10-34J.s, vn tc nh sng trong chn khng c = 3.108m/s. Gii hn quang in ca kim lai l A. 0,295 m B. 0,300 m C. 0,250 m D. 0,375 m

Cu 2. Chiu mt chm bc x c bc sng vo b mt mt tm nhm c gii hn quang in 0,36m. Hin tng quang in khng xy ra nu bng A. 0,24 m. B. 0,42 m. C. 0,30 m. D. 0,28 m.

Cu 3. Bit cng thot ca lectron khi mt kim loi l 4,14 eV. Gii hn quang in ca kim loi l A. 0,50 m. B. 0,26 m. C. 0,30 m. D. 0,35 m.

Cu 4. Cng that lectron ra khi mt kim lai 3,6.10-19J, hng s Plng h = 6,625.10-34J.s, vn tc nh sng trong chn khng c = 3.108m/s. Chiu chm sng c bc sng 0,3m vo kim loi trn. Vn tc ban u cc i ca quang electron l A. 8,15.105m/s B. 9,42.105m/s C. 2,18.105m/s D. 4,84.106m/s

Cu 5. Trong chn khng, nng lng ca mi phtn ng vi nh sng c bc sng 0,75 m bng A. 2,65 eV. B. 1,66 eV. C. 2,65 MeV. D. 1,66 MeV.

Cu 6. Vi 1, 2, 3 ln lt l nng lng ca phtn ng vi cc bc x mu vng, bc x t ngoi v bc x hng ngoi th A. 2 > 1 > 3. B. 3 > 1 > 2. C. 1 > 2 > 3. D. 2 > 3 > 1.

Cu 7. Pht biu no sau y sai khi ni v phtn nh sng? A. Nng lng ca phtn nh sng tm ln hn nng lng ca phtn nh sng .

B. Phtn ch tn ti trong trng thi chuyn ng.

C. Mi phtn c mt nng lng xc nh.

D. Nng lng ca cc phtn ca cc nh sng n sc khc nhau u bng nhau.

Cu 8. Gii hn quang in ca nhm v ca natri ln lt l 0,36 m v 0,50 m. Bit 1eV = 1,6.10-19J. Cng thot ca lectron khi nhm ln hn cng thot ca lectron khi natri mt lng l: A. 0,322 eV. B. 0,140 eV. C. 0,966 eV. D. 1,546 eV. Cu 9. Gii hn quang in ca mt kim loi lm catt ca t bo quang in l 0 = 0,50 m. Bit vn tc nh sng trong chn khng v hng s Plng ln lt l 3.108 m/s v


6,625.10-34 J.s. Chiu vo catt ca t bo quang in ny bc x c bc sng = 0,35 m, th ng nng ban u cc i ca lectrn (lectron) quang in l A. 1,70.10-19 J. B. 70,00.10-19 J. C. 0,70.10-19 J. D. 17,00.10-19 J.

Cu 10. Khi truyn trong chn khng, nh sng c bc sng 1 = 720 nm, nh sng tm c bc sng 2 = 400 nm. Cho hai nh sng ny truyn trong mt mi trng trong sut th chit sut tuyt i ca mi trng i vi hai nh sng ny ln lt l n1 = 1,33 v n2 = 1,34. Khi truyn trong mi trng trong sut trn, t s nng lng ca phtn c bc sng 1 so vi nng lng ca phtn c bc sng 2

A. 5

9. B.

9

5. C.

133

134. D.

134

133.

Cu 11. Chiu ln b mt catt ca mt t bo quang in chm sng n sc c bc sng 0,485 m th thy c hin tng quang in xy ra. Bit hng s Plng h = 6,625.10-34 J.s, vn tc nh sng trong chn khng c = 3.108 m/s, khi lng ngh ca lectrn (lectron) l 9,1.10-31 kg v vn tc ban u cc i ca lectrn quang in l 4.105 m/s. Cng thot lectrn ca kim loi lm catt bng A. 6,4.10-20 J. B. 6,4.10-21 J. C. 3,37.10-18 J. D. 3,37.10-19 J.

Cu 12. Ln lt chiu vo catt ca mt t bo quang in cc bc x in t gm bc x c bc sng 1 = 0,26 m v bc x c bc sng 2 = 1,21 th vn tc ban u cc i ca

cc lectrn quang in bt ra t catt ln lt l v1 v v2 vi v2 = 1

3v

4. Gii hn quang in

0 ca kim loi lm catt ny l A. 1,45 m. B. 0,90 m. C. 0,42 m. D. 1,00 m.

Cu 13. Chiu ng thi hai bc x c bc sng 0,452 m v 0,243 m vo catt ca mt t bo quang in. Kim loi lm catt c gii hn quang in l 0,5 m. Ly h = 6,625. 10-34 J.s, c = 3.108 m/s v me = 9,1.10

-31 kg. Vn tc ban u cc i ca cc lectron quang in A. 2,29.104 m/s. B. 9,24.103 m/s C. 9,61.105 m/s D. 1,34.106 m/s

Cu 14. Bit cng thot lectron ca cc kim loi: canxi, kali, bc v ng ln lt l: 2,89 eV; 2,26eV; 4,78 eV v 4,14 eV. Chiu nh sng c bc sng 0,33 vo b mt cc kim

loi trn. Hin tng quang in khng xy ra vi cc kim loi no sau y? A. Kali v ng B. Canxi v bc C. Bc v ng D. Kali v canxi

Cu 15. Mt kim loi c cng thot lectron l 7,2.10-19 J. Chiu ln lt vo kim loi ny cc bc x c bc sng 1 = 0,18 m, 2 = 0,21 m, 3 = 0,32 m v = 0,35 m. Nhng bc x c th gy ra hin tng quang in kim loi ny c bc sng l A. 1, 2 v 3. B. 1 v 2. C. 2, 3 v 4. D. 3 v 4.

m

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