t vi mú n v mú - · pdf filemỗi hạt sơ cấp có momen ñộng...
If you can't read please download the document
TRANSCRIPT
Bi tp 12 luyn thi i hc - Trn Th An ([email protected] 09.3556.4557) Trang 1
T VI M N V M
A. L THUYT 58. CC HT S CP
1.Ht s cp Cho n nay, ngi ta pht hin c cc ht c kch thc v khi lng rt nh, chng hn nh lectron, prtn, ntron, mzn, muyn, pin. Tt c cc ht ny c gi l ht s cp (i khi cn gi l ht c bn). Ni chung, ht s cp c kch thc v khi lng nh hn ht nhn nguyn t. 2. Cc c trng ca ht s cp Sau y l nhng c trng chnh ca cc ht s cp : a) Khi lng ngh m0 Phtn c khi lng ngh bng khng. Ngoi phtn, trong t nhin cn c cc ht khc c khi lng ngh bng 0, nh ht ntrin v, ht gravitn. Thay cho m0 ngi ta cn thng dng i lng c trng l nng lng ngh E0 tnh theo h thc Anh-xtanh E0 = m0c
2. Chng hn, lectron c m0 = 9,1.10-31kg v E0 = 0,511 MeV ; prtn c m0 =
1,6726.10-27kg v E0 = 938,3MeV. b) in tch Ht s cp c th c in tch Q = +1 ( tnh theo n v o in tch nguyn t e). Hoc Q = -1, hoc Q = 0 (ht trung ho). Q c gi l lng t in tch, biu th tnh gin on ca ln in tch cc ht. c) Spin Mi ht s cp c momen ng lng ring v momen t ring c trng cho chuyn ng ni ti v bn cht ca
ht. Momen ny c c trng bng s lng t spin, k hiu l s. Momen ng lng ring ca ht bng s2
h
( h l
hng s plng). Chng hn, prtn v ntron c spin s =1
2, nhng ptn c spin bng1, pin c spin bng 0.
d) Thi gian sng trung bnh Trong cc ht s cp, ch c bn ht khng phn r thnh cc ht khc, gi l cc ht bn (prtn, lectron , phtn, ntrin). Tt c cc ht cn li l cc ht khng bn v phn r thnh cc ht khc. Tr ntron c thi gian sng di, khong 932s, cn cc ht khng bn u c thi gian sng rt ngn, c t 10-24s n 10-6s. 3. Phn ht a) Phn ln cc ht s cp u to thnh cp, mi cp gm hai ht c khi lng ngh m0 nh nhau, cn mt s c trng khc th c tr s bng nhau nhng tri du. Chng hn, lectron v pzitron c cng khi lng ngh bng me
v spin bng1
2, nhng c in tch tng ng bng +1 v -1, to thnh mt cp.
Trong mi cp, c mt ht v mt phn ht ca ht . Chng hn, pzitron l phn ht ca lectron. Phn ht ca
prtn (gi l antiprtn, k hiu p
), c Q = -1. b) Trong qu trnh tng tc ca cc ht s cp, c th xy ra hin tng hu mt cp ht + phn ht c khi lng ngh khc 0 thnh cc phtn, hoc cng mt lc sinh ra mt cp ht + phn ht t nhng phtn. V d nh qu trnh hu cp hoc sinh cp lectron + pzitron (xem Hnh 58.1):
e e + + + e e + + + 4. Phn loi ht s cp Ngi ta thng sp xp cc ht s cp bit thnh cc ht sau, theo khi lng ngh m0 tng dn. a) Phtn (lng t nh sng ) c m0 = 0.
b)Leptn, gm cc ht nh nh lectron, muyn ( , + ), cc ht tau ( + + ), c)Mzn, gm cc ht c khi lng trung bnh trong khong ( 200900)me, gm hai nhm: Mzn v mezn K. d) Barion, gm cc ht nng c khi lng bng hoc ln hn khi lng prtn. C hai nhm barion l nucln v
hipron, cng cc phn ht ca chng. Nm 1964, ngi ta tm ra mt hipron mi l ht mga tr ( ). Tp hp cc mzn v cc barion c tn chung l cc harn. 5. Tng tc ca cc ht s cp Cc ht s cp tng tc vi nhau nh th no to nn cu trc vt cht, to nn v tr ? c bn loi tng tc c bn i vi ht s cp: a) Tng tc hp dn. l tng tc gia cc ht vt cht c khi lng. Bn knh tc dng ca lc hp dn ln v cng, nhng so vi cc tng tc khc th cng ca tng tc hp dn l rt nh. b) Tng tc in t. l tng tc gia cc ht mang in, gia cc vt tip xc gy nn ma st C ch tng tc in t l s trao i phtn gia cc ht mang in. Bn knh tc dng ca tng tc in t xem nh ln v hn. Tng tc in t mnh hn tng tc hp dn khong 1037ln.
Bi tp 12 luyn thi i hc - Trn Th An ([email protected] 09.3556.4557) Trang 2
H nh 59.1. H e Ma t tr i
....
....
....
....
....
....
....
....
....
....
....
........
....
....
........
....
....
....
....
........
....
....
....
....
....
....
........
....
....
........
....
....
........
........ ....
....
....
....
....
8
76
5
4
3
2 1
....
c) Tng tc yu. l tng tc gia cc ht trong phn r .Chng hn, phn r l do tng tc yu ca bn ht ntron, prn, lectron v phn ntrin theo phng trnh:
n p e v + +
. Tng tc yu c bn knh tc dng c 10-18 m v c cng nh hn tng tc in t khong 1012 ln. d) Tng tc mnh. l tng tc gia cc harn, nh tng tc gia cc nucln trong ht nhn, to ln lc ht nhn, cng nh tng tc dn s sinh ht har trong cc qu trnh va chm ca cc harn, tng tc gia cc ht quac. Tng tc mnh ln hn tng tc in t khong 100 ln v c bn knh tc dng c 10-15m (bng bn knh ht nhn). 6. Ht quac (quark) a) Liu cc ht s cp c c cu to bi cc ht nh hn khng ? Nm 1964, nh vt l Ghen- Man nu ra gi thuyt : Tt c cc harn u cu to t cc ht nh hn , gi l quac ( ting Anh : quark). b) C su ht quac k hiu u, d, s, c, b v t. cng vi cc quac, c su phn quac vi in tch c du ngc li.
iu k l l in tch cc ht quac v phn quac bng 3
e ,
2
3
e tri ngc vi quan nim trc y cho rng in tch
nguyn t e l in tch nh nht. Cc ht quac c quan st thy trong th nghim, nhng u trng thi lin kt ; cha quan st c ht quac t do. c) Cc barion l tng hp ca ba quac. Chng hn prtn c to nn t ba quac (u,u,d), ntron c to nn t ba quac (u,d,d) (Hnh58.2).
Hnh 58.2. C au ta o cua p roton (a ) va n tron (b )
b )a )
d) Mt trong cc thnh cng ca gi thuyt v ht quac l d on c s tn ti ca ht mga tr ( ) (s,s,s), m sau tm ra c bng thc nghim vi y c trng nh d on. Cho n nay, nhiu nh vt l th nhn s tn ti ca ht quac v nh vy, cc ht thc s l s cp (hiu theo ngha l ht khng th tch c thnh) cc phn nh hn ) ch gm cc quac, cc leptn v cc ht truyn tng tc.
59. MT TRI H MT TRI
1. Cu to v chuyn ng ca h mt tri a. H mt tri bao gm - Mt Tri trung tm H (v l thin th duy nht nng sng) ; - Tm hnh tinh ln: xung quanh a s hnh tinh ny cn c cc v tinh chuyn ng (Tri t c mt v tinh l mt trng) ; - Cc hnh tinh t hon gi l tiu hnh tinh, cc sao chi, thin thch gia qu o ho tinh v mc tinh ngi ta pht hin c hng ngn tiu hnh tinh. - Nu k t mt tri ra xa, th tm hnh tinh ln ln lt c tn gi l: Thu tinh (cn gi l sao thu), kim tinh (sao kim), Tri t, Ho tinh (sao Ho), Mc tinh (sao mc), Th tinh (sao th), Thin vng tinh (hay thin tinh), v Hi vng tinh (hay hi tinh). o khong cch t cc hnh tinh n Mt tri, ngi ta dng n v thin vn (k hiu vtv). 1vtv bng khong cc t Tri t n Mt tri, xp x bng150 triu kilmt. b) iu ng ch l tt c cc hnh tinh u chuyn ng quang Mt tri theo cng mt chiu (chiu thun), v gn nh trong cng mt mt phng. Mt tri v cc hnh tinh u quay quanh mnh n v u quay theo chiu thun (tr kim tinh). Ton b h Mt triquay quanh trung tm thin h ca chng ta (xem bi 60).
Bi tp 12 luyn thi i hc - Trn Th An ([email protected] 09.3556.4557) Trang 3
c) Bit chu k v bn trc ln ca qu o ca cc hnh tinh ( xc nh c bng phng php thin vn o lng) t nh lut III K-ple ngi ta tm thy rng khi lng ca Mt tri ln hn khi lng ca Tri t 333 000 ln, tc l bng 1,99.1030kg (!). 2. Mt tri a) Cu trc ca mt tri: Nhn tnh qut, Mt tri c cu to gm hai phn l quang cu v kh cu. * Quang cu. Nhn t Tri t ta thy Mt tri c dng mt a sng trn v bn knh gc 16 pht ( Hnh 59.5). khi cu nng sng nhn thy ny c gi l quang cu ( cn gi l quang quyn, c bn knh khong 7.105 km). Khi lng ring trung bnh ca vt cht trong quang cu l1400kg/m3. Cn c vo nh lut bc x nhit ngi ta tnh c nhit hiu dng ca quang cu vo khong 6000 K, cn nhit trong lng Mt tri vo c trn chc triu . * Kh quyn Mt tri. Bao quanh quang cu c kh quyn Mt tri. Kh quyn Mt tri c cu to ch yu bi hir, heli v c nhit rt cao nn kh quyn c c tnh rt phc tp. Kh quyn c phn ra hai lp c tnh cht vt l khc nhau l sc cu v nht hoa. Sc cu l lp kh nm st mt quang cu c dy trn 10 000 km v c nhit khong 4500k. Pha ngoi sc cu l nht hoa (Hnh 59.6). Vt cht cu to nht hoa trng thi ion ho mnh (gi l trng thi plaxma). Nhit khong 1 triu . Nht hoa c hnh dng thay i theo thi gian. b) Nng lng ca Mt tri Mt tri lin tc bc x nng lng ra xung quanh. Lng nng lng bc x ca Mt tri truyn vung gc ti mt n v in tch cc n mt n v thin vn trong mt n v thi gian c gi l hng s Mt tri H. Kt qu o H cc i vt l a cu trn th gii v trn cc trm v tr ngoi kh quyn cho thy H c tr s nh nhau v H = 1360W/m2 . T suy ra c cng sut bc x nng lng ca Mt tri l P= 3,9.1026W ! Kt qu o hng s Mt tri t nhiu nm nay cho thy tr s ca H khng thay i theo thi gian. S d Mt tri duy tr c nng lng bc x ca mnh l do trong lng Mt triang din ra phn ng nhit hch. c) S hot ng ca mt tri * Qua cc nh chp mt tri trong nhiu nm, ngi ta thy quang cu sng khng u, c cu to dng ht, gm nhng ht sng bin i trn nn ti, do s i lu t trong lng Mt tri i ln m thnh ( Hnh 59.5). tu theo tng thi k cn xut hin nhiu du vt khc : vt en, bng sng, tai la. Vt en c mu sm ti, nhit vt en vo khong 4000k (Hnh 59.7 a). Thng th t khu vc xut hin vt en c ko theo nhng bng sng. T cc bng sng ny phng mnh ra tia X v dng ht tch in (c gi l gi Mt tri). Ngoi ra cn c nhng tai la, l nhng li la phun cao trn sc cu (Hnh 59.7b). * Nm Mt tri c nhiu vt en nht xut hin c gi l nm Mt tri hot ng. Nm Mt tri c t vt en xut hin nht gi l nm Mt tri tnh. Qua theo di t u th k XIX n nay, ngi ta thy s hot ng ca mt tri din ra theo chu k v c lin quan n s vt en trn Mt tri. Chu k hot ng ca Mt tri c tr s trung bnh l 11 nm. 3. Tri t: Tri t chuyn ng quanh Mt tri theo mt qu o gn trn. Trc quay ca Tri t quanh mnh n nghing trn mt phng qu o mt gc 23027. a) Cu to ca Tri t Tri t c dng phng cu ( hi dp hai cc ), bn knh ca xch o bng 3678 km, bn knh hai cc bng 6357 km. Khi lng ring trung bnh l 5520 kg/m3 (Hnh 59.8). Da vo cc nghin cu tnh cht truyn sng a chn, ngi ta cho rng Tri t c mt ci li bn knh vo khong 300 km, c cu to ch yu l st, niken (nhit phn
ny vo khong 30004000 0C ). Bao quanh li l lp trung gian, v ngoi cng l lp v dy khong 35 km c cu to ch yu bi granit.Vt cht trong v c khi lng ring 3300 kg/m3. b) Mt Trng- v tinh ca Tri t Mt trng cch Tri t 384 000 km c bn knh 1738 km, c khi lng 7, 35.1022 kg (Hnh 59.9). Gia tc trng trng ca Mt trng l 1,63 m/s2. Mt trng chuyn ng quanh Tri t vi chu k 27,32