Solutions Quantum Physics - R. Eisberg & R. 2nd Resnick

209
S olut ions S up plem ent t o Accompany QUANTUM PHYSICS OF A TO MS, MOLECULES, SOLIDS, NUCLEI, AND P ARTICLES Second Edition Robert Eisberg Robert Resnick P repar ed by E dw ar d Derr ing h

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Solutions Quantum Physics - R. Eisberg & R. 2nd Resnick

Transcript of Solutions Quantum Physics - R. Eisberg & R. 2nd Resnick

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    Solutions Supplement to Accompany

    QUANTUM PHYSICSOF ATOMS, MOLECULES, SOLIDS,NUCLEI, AND PARTICLES

    Second Edition

    Robert Eisberg

    Robert Resnick

    Prepared by Edward Derringh

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    Thi s suppl ement contai ns sol ut i ons t o mast of themore- i nvol ved probl ems i n the CUANI UMPHYSI CS text ;wi t h one except i on, sol ut i ons t o probl ems i n theAppendi ces are not i ncl uded.

    The suppl ement i s di rected toward i nstructors, andthi s has i nf l uenced the presentat i on. Mot every

    al gebrai c st ep i s exhi bi ted. The uni t s have not beendi spl ayed expl i ci t y i n every equat i on. (SI uni t s areadopt ed i n the suppl ement , mai nl y because t hey arebr i ef er than the text notat i on. ) Rul es wi t h regardto si gni f i cant f i gures have not been str i ctl yobserved, al t hough there shoul d be no out l andi shvi ol at i ons. Use of symbol s and choi ce of notat i oni s general l y obvi ous and theref ore r ot exhaust i vel ydef i ned f or each probl em.

    I t I s a pl easure t o thank Prof . Ri char d Shurt l ef f(Wentworth I nst i tut e of Technol ogy) f or prepar i ngt he sol ut i ons t o t he probl ems i n Chapt er 18.

    Preparat i on of t he suppl ement , i ncl udi ng choi ce ofprobl ems, was l ef t t o the undersi gned, whs was al sohi s own typi st and i l l ustrator. He woul d appreci atea note, of up t o moderat e asper i ty, f romt hose whodet ect an er ror and/ or mi stake.

    Decenfcer 24, 1984 Edward Derr i ngh

    41 Montgomery Dr i vePl ymouth, MA 02360

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    Chapt er O n e . . . . . . . . . . . . . . . . . . . . . . . . . 1

    Chapt er TMd . . . . . . . . . . . . . . . . . . . . . . . . . 7

    Chapt er Thr ee . . . . . . . . . . . . . . . . . . . . . . . . . 13

    Chapt er Four . . . . . . . . . . . . . . . . . . . . . . . . . 18

    Chapt er F i v e . . . . . . . . . . . . . . . . . . . . . . . . . 27

    Chapter S i x . . . . . . . . . . . . . . . . . . . . . . . . . 41

    Chapter Seven . . . . . . . . . . . . . . . . . . . . . . . . . 59

    Chapt er Ei ght . . . . . . . . . . . . . . . . . . . . . . . . . 72

    Chapt er Ni n e . . . . . . . . . . . . . . . . . . . . . . . . . 85

    Chapt er T e n . . . . . . . . . . . . . . . . . . . . . . . . . 98

    Chapt er El even . . . . . . . . . . . . . . . . . . . . . . 112

    Chapt er T we l v e . . . . . . . . . . . . . . . . . . . . . . 126

    Chapt er Thi r t een. . . . . . . . . . . . . . . . . . . . . . 136

    Chapter Four teen . . . . . . . . . . . . . . . . . . . . . . 152

    Chapter Fi f teen . . . . . . . . . . . . . . . . . . . . . . 160

    Chapt er S i x t e e n. . . . . . . . . . . . . . . . . . . . . . 169

    Chapt er Seventeen . . . . . . . 183

    Chapter Ei ghteen . . . . . . . . . . . . . . . . . . . . . . 194

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    CHAPTER ONE

    The radi ant enerqy cont ai ned i nvol ume dv t hat i s i rovi nq towardA at any t i me, i n t he f requencyi nterval v, v+dv i s

    dEp( v)dv = ppl vl dv ^ dV,

    where fi i s t he sol i d anql esubtended at dv by A. Wi t h

    = Acose/ r2

    dv = r2si n6drd0d.

    the enerqy beccroes

    dE , (v)dv = pT (v)dv Asi n0cos6drd0d4i .

    The energy i n thi s f requency i nterval that crosses A i n t i me tf rcmthe ent i re upper hemi sphere i s

    rv/2 r2 T\ i-ct

    E , (\>)dv = Apf vl dv ^ I I I si necosSdedi j i dr

    J 0=ol

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    i d

    P=ABT

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    (a) L = 4 t iP2oT 4 = 41,(7 X 108 ) 2 (5 .6 7 x 10~8) (570 0)4 ,

    L = 3 .6 8 5 x 1026 W.

    r _

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    (b) 338 = oT4 = (5. 67 X 10_8)T4,

    T = 280 K.

    1-19

    c . 2*k5T5 x5v x > W x> T t r X

    h e e - 1

    wi t h x = he/XkT. At X = max, x = 4. 965, by Probl em

    VNnax' = 42 403,1 ( W) 5/ h4c3.

    Now f i nd x such t hat ( X) = 0-2RT (Xmax>!

    2nk5T5 x5 k5T^", i -rr-- - (0 . 2)42. 40371 7 ,h e ex - 1 h V

    If

    4. 2403,

    xx = 1. 882, x2 = 10. 136.

    Numer i cal l y,

    1 = he 1 (6. 626 x 10~34) (2. 998 x 108) 1

    x (1- 38 x 10- 23) (3) x'

    X = 4. 798 x 10' 3/ x ,

    so that

    Xx = 4. 798 x 10- 3/ 1. 882 - 2. 55 mn,

    X2 = 4. 798 x 10- 3/ 10. 136 =0. 473 nm.

    1-20

    I f x = hc/XmaxkT, then, by Probl em18,

    . Thus,

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    s

    5 - x

    Hence,

    t (wmax

    But,

    x = 4.965;\nax

    Upon subst i tut i on, these gi ve

    x = 4.965; -f-= (4.965 j^) 4.

    r W = 170"(he)

    1 - 2 1

    By Probl an 20,

    pT = 170"T mBX (he)4

    so that the wavel engt hs sought must sat i sf y

    ^ hcTxkT - - 170, - 4 .Xs e ' - 1 (he)4

    Agai n l etx = hc/ XkT.

    I n t erms of x, t he precedi ng equat i on beoanee

    x5 _ 170

    ex - l " 16 '

    Sol ut i ons are

    Xx = 2. 736; = 8. 090.

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    Si nce, f or X ^,

    these sol ut i ons gi ve

    X1 - 1-B15W -

    X2 = *614W

    1-24

    Let X' = 200 nm, X" = 400 nm; then.

    1 ______1_____ ,, 1 _______1x, 5 ehc/ X' kT _ ~ (3-82) x5 ehc/ x"kT _ ^

    hc/ X- kT _ .

    ehc/ XkT _ 382

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    CHAPTEK TOO

    The photoel ect r i c equat i on i s

    he = eVQX + wQX.

    Wi th VQ = 1. 85 V f or X = 300 nm, and VQ = 0. 82 \

    he = 8. 891 x K f 26 + 3 x 10' 7wQ,

    he = 5. 255 x 10- 26 + 4 x 10_7wQ.

    Hence,

    8. 891 x 10"26 + 3 x 10~7w0 = 5. 255 x 10- 26 +

    (b) wQ = 3. 636 x 10_19 J = 2. 27 eV.

    Theref ore,

    he = 8. 891 X 10- 26 + (3 X 10- 7) (3. 636 X ]

    he = 19. 799 x 10- 26 J - m,

    (fl) h . 19 ,?9 9_x. . 101 6 = 6-6Q4 x 10-34 ,2.998 X 10

    (c) wQ = hc/ X0,

    3. 636 X 10-19 = 19. 799 x 10_26/ X0,

    Xq = 5. 445 x 10 7 m= 544. 5 nm.

    2-8

    I n a magnet i c f i el d

    r = mv/ eB.

    4 x 10

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    p = mv = erB = (1. 602 x 10- 19) (1. 88 x 10- 4),

    p = 3. 012 x 10- 23 k - m/ s,

    (3. 012 x 10~23) (2. 998 x 108) _ 0. 05637 MeV

    Al so,

    Hence,

    (a)

    c (1.602 x 10- 13)

    E2 =P 2C2 + E2,

    E2 = (0. 05637)2 + (0. 511)2,

    E = 0. 5141 MeV.

    K = E - E 0. 5141 - 0. 5110 = 0. 0031 M6V.

    (b) The pbDt cmenergy i s

    1240Eph(eV>= S = 0 7 1 = -0175 M6V!

    wo - Eph - K - 17-5 - 3. 1 = 14. 4 keV.

    2- 9

    (a) Assumi ng t he process canoperate, appl y conservat i on ofmass- energy and of momentum:

    hv +E0

    K + Eq hv Ks

    *1!

    These equat i ons t aken t oget her i npl y that

    P = K/ c.

    But , t or an el ectron,

    E2 = P2c 2 + E ,

    (K + Eq)2 - p2c2 + E*

    (*)

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    p = / ( K2 + 2EQK) / c. (**)

    (*) and (**) can be sat i sf i ed together onl y i f Ep ^ 0, whi ch i snot t rue f or an el ectron.

    (b) I n the Compton ef f ect , a photon i s present af ter thecol l i si on; thi s al l ows t he conservat i on l aws t o hol d wi thoutcontradi cti on.

    2-14

    Let n = number of phot ons per uni t vol ume. I n t i me t, al l

    photons i ni t i al l y a di stance < ct wi l l cross area A normal t othe beamdi rect i on. Thus,

    = Energy = n(hv)A(ct}_ = nhcv = nh_At At X

    For two beams of wavel engths X and X2 wi t h 1 =

    f i =, = ni A i + Hi ,I 2 n2/ X2 n2 X2'

    and theref ore

    n / At X

    n2/ At ~ X2

    The energy densi t y i s p = nhv = nhc/ X. Si nce thi s di f f ers f rom

    onl y by the factor c (whi ch i s the same f or bot h beams) , then :Px = p2, t he equat i on above hol ds agai n.

    2-26

    Set = 20 keV, Kf = 0; K1 = el ect ron ki net i c energy af t er the

    f i rst decel erat i on; then

    l J = Ki - Ki : r2 = K1 - Kf - Kr *2 = xi + fi x'

    wi t h AX = 0. 13 nm. Si nce

    he = 1. 2400 keV-nm,

    hh

    W

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    these equat i ons beccme

    1. 240020 - K, ;

    Sol vi ng yi el ds,

    (a) Kx - 5. 720 keV;

    ( W 0. 0868 rm; X2 - 0. 2168 i m.

    2- 28

    Appl y the l aws of conservat i on of total energy and of i ranentam.Cent er of Mass Frame

    r-VUVUUU-*

    Theref ore,

    i t r o t

    E1 + me2 - i i c2,

    - mv = 0.

    mv + me 3mgC,

    m( l + B) 3n ,

    ^ 2 I "

    8 - 4/ 5.

    Hence, m - 5m/ 3 and E' - mc2B - 4UC2/ 3. By the Docpl er shi f t ,wi t h B = 4/ 5, ~

    E' = E{( 1 - B) / ( 1 + B)}%= E/ 3,

    E - 3E' = Sl OgC2) - 4b1qC2.

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    Laboratory Frame

    ' VWl Ar

    - -

    -

    X

    %

    Theref ore,

    bo that

    2-29

    (a)

    (b)

    E + m c2 = 3 0 + 3K,

    E/ c = 3(K2 + 2mQc2K) Vc .

    2it1qC2 + 3K = 3( K2 + 2mQc2K)

    K - |V 2'

    E = 2mQc2 + 3K = 4mQc2.

    E + Mqc 2 = Mqc2 + 2mQc2 + K,

    E - 2(0. 511) + 1 = 2. 022 MeV.

    p = E/ c = 2. 022 MeV/ c; p+ = 0;

    p_ - i (K2 + 2m()c2K) %= i {l 2 + 2(0. 511) (1)}%= J

    P = (2. 022 - 1. 422) = 0. 600 MeV/ c;

    %transf erred =

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    Use t he Doppl er shi f t t o conver t t he gi ven wavel engths t o

    wavel engths as seen i n the rest f rame of the pai r:

    2XJ = \'2,

    4 1 - P , 1 +1 + B 1 - B'

    3B2 - 10B + 3 = 0,

    B =i ; v = f .

    2-33

    The ramber of par t i cl es st opped/ scattered between di st ances xand x-tdx i s dl (x) = oI (x)pdx. Hence, f or a ver y thi ck sl ab thatul t i mat el y stops/ scat ters al l t he i nci dent part i cl es, t heaverage di st ance a par t i cl e travel s i s

    . . f l SS . gp/ xl dx _ x e ^_ dx

    av / dl op/ I dx fe~xdx ap

    t he l i mi t s on al l x i ntegral s bei ng x = 0 to x = .

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    CHAPTE2? THREE

    f c iX h/ m .

    x _ e e* x h/mxv - m - v -

    Xe mx vx'

    1. 813 x l O- ^- 9- 9- ^10-"31^ ),mx 3

    mx = 1. 675 x l ( f 27 kg;

    vl dentl y, the par t i cl e i s a neutron.

    3-7

    (a) E2 =p 2c2 + E ; (K + Eq)2 = p2c2 + E ,

    Ri t K = eV and Eg = m c2, so that

    . 2KE- , 2(eV) ( mc2) ,

    C (2KEq) = ( )* = {- - - - - 2^-- ) = / ( 2meV) ,c c

    and

    K/ 2EQ = eV/ 2m0c2.

    Theref ore,

    X =$ = 77 47r ( l + - ^ r ^ .p = 7( i v r l i + c2

    (b) Nonrel at i vi st l c l i mi t : eVmgC2; set 1 + eV/2rruc2get J

    X =h/ ( 2m0eV)' ! = h/ ( 2m0K)' s =

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    Numeri cal l y,

    hence.

    bj. = (6. 626 x 1Q- 34 J s) (2. 998 x 108 m/s)

    (1. 602 x 10- 13 J / MeV) ( 10- 9 m/ m)

    he = 1. 2400 x 10"3 MeV- nm;

    . . . . 1. 2400 x 10~3 MeV- r mj l - f,2)'5*' ' Eq (MeV) B

    3-19

    (a)

    p = h _ 6. 626 x 10~34 J - s (2. 998 x 108 m/ s) = 0. 12400 MeVX (10- 11 n0 c (1. 602 x 10- 13 J / MeV) c

    E2 = (0. 1240)2 + (0. 511)2 E = 0. 5258 MeVs

    K * E - E0 0. 5258 - 0. 5110 - 0. 0148 MeV - 14. 8 keV.

    ( t>) _

    P - V 124kev-These are qartma-rays, or hard x- rays.

    (c) The el ect ron mi croscope i s pref erabl e: t he gamna- rays aredi f f i cul t t o focus, and shi el di ng wcul d be requi red.

    3-28

    (a) Set Ax = 10- 10 m.

    _ h _ _ 6. 626 x 10~34 J - s

    P_4P **

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    = 5. 2728 x 10~25 kg- m/ s 2. 998 x 10R m/ s = 0. 9868 keV_

    c 1. 602 x 10- 16 J / keV c

    E = Ax, f or the anal l est E use px = Apx

    and x = Ax to obt ai n

    E =

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    E = to(4ik >2 +!>C(to>2 =-~ A ,2 +32n m(Ax)

    (b) Set t he der i vat i ve equal t o zero:

    = _ +C( f i x) =0 *

    Subst i t ut i ng thi s i nto t he expressi on f or E above gi ves

    Emi n * " "

    3-34

    (a) Let the crack be of zero wi dt h and Ax * hor i zontal ai mi nger ror (i . e. , drop poi nt not exact l y above crack) . I bi s i npl i esan i ni t i al hor i zontal speed v^ gi ven by

    v = Avx x mAx

    As a resul t of thi s, t he bal l l ands a hor i zontal di stance x f rant he rel ease poi nt , gi ven by

    Hence, t he total hor i zontal di st ance X f ran crack t o i i rpactpoi nt i s

    X = AX + x - A X +

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    Put an el ect ron behi nd each

    sl i t and observe any recoi ldue t o i ts col l i si on wi t h aphoton emergi ng f ran thesl i t , l b det ermi ne whi chel ectron recoi l ed, i t s observeddi spl acement ay must sati sf y

    Ay W,

    at l east, or even

    W

    X

    Ay 4J .

    Due t o the col l i si on, t he ptoton' s manent umchanges. I n ordernot t o dest roy the i nter f erence pat tern,

    mX _ mh _ j nh.px 6 - d - pd - pxd-

    Py T d'

    m the order of the f r i nge. By conservat i on of manentun, thi s i sal so the uncer t ai nt y i n t he el ect ron' s rranentum. Hence, f or theel ect ron, i t i s r equi red that , i n order not t o dest roy thepattern,

    (Ay) = W.

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    CHAPTER FtXI R

    4=1

    Consi der an el ect ron osci l l at i ng al ong a di aneter . When at adi stance r f ran t he cent er of t he atom, t he f or ce on t he el ectroni s

    F =

    where p = e/ ( 4nR3/3) > 0 si nce the net charge on atai t-el ectroni s +e. Theref ore,

    - - - r.4tte0

    Thi s f orce i s at t ract i ve: i . e. , di rect ed t cward t he cent er of theatcm. Hence,

    F - ma.

    I f t he el ect ron revol ves i n a ci r cul ar orbi t of radi us R,

    F ma.

    The t wo f requenci es are seen t o be equal . The equal i t y appl i esal so to osci l l at i ons of arpl i t ude l ess t han R and ci r cul arorbi t s of radi us l ess t han R, si nce t he charge ext er i or t o theanpl i t ude or radi us exer t s zero f orce on t he el ectron f orspher i cal l y symmet r i c charge di st r i but i ons.

    4-4

    (a) Manent amconservat i on:

    Mv = MucosS + mwcos*,

    Musi nS = i twsi n*.

    I B

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    Ki net i c energy conservat i on:

    IjMv 2 = Mu2 + !smw2-

    The r rcmentumequat i ons gi ve:

    mwcosi j ) = M( v - ucos8)mwsini ti = Musi n8.

    Hence, 2 2 2 2 2mw = tr(v - 2uvcos6 + u ).

    The energy equat i on yi el ds

    m2w2 = Mn( v2 - u2) .

    Equati ng the t wo expressi ons f or m2w2:

    M2 (v2 - 2uvcos6 + u2) = Mn( v2 - u2),

    cos0 = &U-B> + +

    (Si nce m 0, a mi ni numf or cos0, a maxi i mmf or 0.

    Subst i t ute thi s val ue of u i nto the equat i on f or cos0 to get

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    The maxi nun f orce f el t by the al pha- par t i cl e i n passage throughthe at omoccurs at t he aton' s surf ace:

    p = _ 1 _ (Ze]. L2eIit. 4ne0 r 2

    For maxi mumdef l ect i on, suppose thi s f orce i i rparts trcmentun Apperpendi cul ar t o t he or i gi nal di rect i on of mot i on:

    Ap = J Tdt = Fm(At) .

    _ 1 4Ze2^ " 4ne0 Rv -

    Then, ant i ci pat i ng a smal l def l ect i on 8,

    Aj>= 1 2Ze2 _ Usurf

    rav 4e0 R( %Mv2) Ka

    For gol d, Z = 79; suppose Kq = 5 MeV; then

    6 = (8 .9 88 X 109)

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    . 1 . 2 ,zZe2,2. 1dN = (-7 ) (-- ?) I n-- j - - - -

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    The per i ods of revol ut i on of el ect ron and prot cn are equal :

    2 n e2nrp

    v_ = v ve P

    v = (-Ej v .p e e

    The not i on i s abcut t he cent er of mass of t he el ect ron- proton

    syst em, so thatr_ m

    V pr = m r -E = .ee re

    Theref ore,m

    v.

    4- 22

    (a) Frequency of t he f i rst l i ne: = c/ X1 = cH{- - - - -m (nr+1)

    Frequency of t he ser i es l i mi t : = c/\a = - 0).m

    Theref ore, ^

    Av " v - v. - - - - - - r.1 (m+1)

    (b) 2Avl v < y ( ^ > 2

    i vPf cKj j / f S+X)2

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    (l>)

    t - i 2

    K = 26. 6 - 10. 2 = 16. 4 eV.

    Eph, l = 13- 6 + 16- 4 = 30- eV-

    (n) By nonentumconservat i on,

    i!H = Mv.c

    (' i i rbi ni ng t hi s wi t h energy conservat i on gi ves

    fiE = hvn = hv + >jMv2 = hv + lsM( ) 2 = hv + - r - .0 ^ 2Mc

    0 2Mc 2Mc

    v0 = v , l + ^ , ,

    (b) Si nce \) = c/ X, vQ = c/ XQ,

    &E = (13. 6) - A) = 12. 089 ev.1 3

    Negl ect i ng recoi l s

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    Wi t h recoi l :

    f _ J S , . --------(1 2.0 89 ) (1 .6 02 . x. 1 0 -191 _ _ 6 . 440 x lt f 9 ,

    A0 2Mc^ (2) (1. 673 x 10 ) (2. 998 x l o V

    AX = 661 am.

    4- 34

    Hi e ki net i c enerqy of t he el ectron i s

    K = (0. 511 MeV) (/ i -" p 11

    g = 0.0400,2. 998 x 10

    t hi s gi ves K = 409. 3 eV. For hel i i m, t he second i oni zat i onpotent i al f r an the gr ound state i s

    , a 4 , W.ftffl.2. . 54.4eV.i on n2 x2

    Hence,

    4-38

    E ^ = 54. 4 + 409. 3 = 463. 7 eV,

    , _ 1240463. 7

    2. 674 nm.

    (a) Hydrogen Hq : Xj j1 =

    Hel i um, Z = 2: X^1 = 4 1 ^ - ^> =

    I f XH = XHe' 2 = nf / 2 - nf = 4,

    3 = nj / 2 -* n = 6.

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    (Ii) Nowt ake i nto account t he reduced mass y:

    _ i _ 2 = (_ L , 2 = hf e 4ne0 4*K3c 4"0 4n3c h ^

    mm m m (4m) m

    ^ ~me-Hnp =rae(1 " nip1' pHe ~ ( 4 ^) ^ =me (1 ~ Ini 1'

    Theref ore,

    He V

    no that

    X = >4rh4 - t|}-

    l l once, compared to the hydrogen Ha l i ne, the hel i um&4 l i newavel ength i s a l i t t l e shorter.

    (b) Si nce X ji * ( the f actor Z2 i s combi ned wi t h 1/ n? - 1/ n?

    to gi ve equal val ues f or H and He) , 1

    XH ~ He _ He ~ h . _ _H_

    *H He He*

    M _1 - me/mp _ 3 ^ _ 1 0, 511 = -4

    xH 1 - ^ 7 % 4 p 4 938-3 '

    AX = (4. 084 x 10- 4) (656. 3 nm) = 0. 268 nm.

    4-42

    Hi e i ranentun associ at ed wi t h t he angl e 8 i s L = I u. The totalenergy E i s

    E = K = %Ioi2 = jr.

    L i s i ndependent of 6 f or a f reel y rot at i ng obj ect. Hence, by

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    t he Wi 1 son- Scnmer f el d rul e,

    i Ld0 = nh,

    LSI de = L(2t i) = / (2IE) (2n) = nh,

    A/ ( 2I E) = nj i ,

    E =

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    CHAPTER FI VE

    'J J

    In) The t i me- dependent part of t he wavef unct i on i s

    e- l j i t/ (C/m) = e- i Et / K = e-i2irv)t_

    'l1Tef ore,

    ft'1 * 2 *

    (l>) Si nce E = hv = 2u)lv,

    E =

    (-) The l i mi t i ng x can be f ound f ran

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    Hence, the desi red probabi l i t y i s gi ven by

    Prob. = L V l O n l x 2^ .(nH) ln

    I f u = - ^ x .

    "fc

    Prob. *=2l 7 ^ - e"2/ 2du = 2(0. 42) = 0. 84.

    The l ast i ntegral i s t he normal probabi l i t y i ntegral .

    5-7

    (a) Si nce

    V =

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    Put t i ng these i nto Schrodi nger ' s equat i on qi ves

    i , thi sI wxmes

    1 = 2A2| si n2(2i Tx/a)dx = - A2 I sJ o " J o

    si n2udu = A2 ?,

    A = / 0 .a

    (b) Thi s equal s the val ue of A f or the ground st at e wavef unct i onnd, i n f act , t he normal i zat i on const ant of al l t he exci t ed

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    states equal s t hi s al so. Si nce al l of t he space wave f unct i onsare si npl e si nes or cosi nes, t hi s equal i t y i s understandabl e.

    5-11

    The wavef unct i on i s

    = (f | lisi n(27i x/ a)e"i Et/ >i ,a

    and theref orer+a/2

    x = ~l x si n2(2ti x/a)dx = 0.

    J-a/ 2

    As f or x2: r+a/2 2

    x2 = - l x2 si n2(2nx/ a)dx = - -=\u2si n2udu = -t(-|-- >)a2,

    J -a/2 24 >

    x2 = 0. 07067a2.

    5-12

    The l i near moment umoperat or i s -i tf and theref ore

    r+a/ 2 r

    = - \ s i r 3^ {- i H ( s i n ~) }dx = - - As i nu cosu du = 0.

    J - a/ 28 J oP " a\elrrT = a

    Si mi l ar l y, f +a/ 2 2

    3x2

    _ r+p2 = Ms i n f i 2*2 ( s i n ^J d x ,

    a] a rw* aJ' a/2

    r712 = - 8ni 2 ( ) 2i si n2udu = 4it2 $ 2 = 2 .

    J o

    P ---------- . . .

    5-13

    Let Ax = (x2)1*; tsp = (p2) 1.

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    Hence,

    Ax4p = (na) (|) = 4mi (*) = ( | n2 - 2) 1* | = 3. 34 | .

    (b) I n the ground state,

    AxAp = (0. 18a) ( ) = 1. 13

    I n t he f i r st exci t ed stat e t he uncer tai nt i es i n posi t i on andnement umboth i ncrease over t he ground st at e val ues, due to thel i i gher energy of t he part i cl e.

    5-14

    Hi e normal i zed wavef unct i on i s

    _ (On)1/ 8 V( Cm) x2/ 2K - i Et / KT /A K e

    (irW 7

    wi t h E =

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    5 . i a 4 ^V ^^d x ,

    Jo

    0 = & * 4 =* - w -(b) Thi s same rel at i on, U = T = *jE, i s obeyed by the cl assi calosci l l at or al so.

    5-15

    Use t he notat i on

    dx.( xp>i = - i ^ x f dx, , xp) 2 = - i n j f ^

    Cl ear l ypH

    (xp) 2= - i nW*( x + V) dx = ( xp^ - 1#,

    i mpl yi ng that (i gi ^ and (xp>2 cannot bot h be real . Al so, byi ntegrat i ng by

    f +CD+ r f

    (xp) 2 = - i H{xy*y| - \ x-f ^d x } = my

    Thus,(xp)2 = (xp)*.

    I f (xp)1 i s real , thi s l ast rel at i on says t hat (xp)2 i s real

    al so, whi ch cont radi cts the f i r st f i ndi ng above. Hence (xp)^ i s

    carpl ex and t heref ore so i s (xp)2- I fowt ry

    x) V dx;

    xp = fc{(xp>1 + (xp)2) = >s{(xp)1 + (xp) *>,

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    xp = Re(xp) 1#

    so that thi s new xp i s real , as desi red.

    5-21

    Wi t h V = 0, t he energy of t he phot on i s

    E = pc.

    Repl aci ng t he energy E and moment ump by t hei r operators gi ves

    i t * = - i *cf *.

    Now set (x, t ) = i |i (x)T(t) and di vi de the equat i on by T to get

    --afeii =K'where K i s i ndependent of x and t. Wr i t e K = k>tc and the t woequat i ons di rect l y above become

    = - i kcT + T e_i kct ,

    | * =i k* - * = ei kx.

    Hence, f or t he photon,

    y a ei k( x- ct ) _

    5-22

    (a), (b) The curvature of ip i s proport i onal t o | v - E| : where|v - E| i s l arge the f unct i on osci l l ates rapi dl y i n x, andwhere | V - E| i s smal l i t osci l l at es l ess rapi dl y (hence, nodesare cl ose t oget her i n the f ormer case, f ar t her apar t i n thel at ter) . I n t he f i r st state, | v - E| i s j ust l arge enough toturn over: no nodes. The 10t h st at e wi l l have 10- 1 = 9 nodes,l eadi ng t o an odd f unct i on si nce V i s synmet r i cal about theori gi n. The wavef unct i on decays exponent i al l y wherever V>E, the

    cl assi cal l y f orbi dden regi on. For f ur t her di scussi on, seeExampl e 5- 12, whi ch t reat s the si mi l ar si mpl e harmoni coaci l l at or potent i al .

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    'E/C

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    (c) Cl assi cal l y, the probabi l i t y densi t y f unct i on P i s gi ven by

    P = B2/v

    ,B2 the normal i zat i on constant . Energy conservat i on gi ves v:

    E = %mv2 Cx,

    the upper si gn f or x>0. Usi ng thi s,

    P = B2(| ),s(E + Cx)"*.

    Tto determi ne B, use the normal i zat i on condi t i onf C f + E / C

    9 v

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    5- 25

    Wi t h no bump, t he wavef unct i on wi l l be si nusoi dal i nsi de thecl assi cal regi on of not i on and a decayi ng exponent i al outsi de.The l owest energy wavef unct i on wi l l contai n no nodes.I n t he present si tuat i on, i n t he regi on of the turrp thecurvat ure of the wavef unct i on wi l l be l ess t han cut si de thebump, si nce t he cur vat ur ei s propor t i onal t o E - V. Thi s wi l l

    upset t he good behavi or of the wavef unct i on at l arge xassoci at ed wi t h the val ue E, cor respondi ng t o t he f i r st boundstate wi t hDUt the bump. Tto compensate f or t hi s reducedcurvature i n t he regi on of t he bump, a l arger curvature (ascanpared wi t h t he no- bump case) i s needed out si de t he bump.Here V = 0 so t hat the curvat ure i s propor t i onal t o E. Hence,a l arger E i s requi red: t hat i s, the f i r st ei genval ue wi t h t umpi s great er than t he f i r st ei genval ue wi t hout t he bunp.

    5- 25

    By assumpti on.Eh = E1 + / V*VbVdx,

    Vb = bump potent i al energy, - wavefunct i on wi t h no t xnp i n thi

    potent i al . The i ntegral i s t he area under a curve of Y*Vb vs x

    Now vb = 0 except where i t i s equal t o VQ/ 10. Cl ear l y t he area

    wi l l be l arger i f t he bump i s l ocated wher e * i s rel at i vel yl arge (i . e. , i n the cent er f or f j ) t han i f t he I xmp i s pl aced

    wher e * i s smal l , i . e. , at t he edge i n thi s case. Evi dent l ythen. Eh i s l arger f or t he cent ered bunp.

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    Schrodi nger ' s equat i on i s

    + % E - V)4. = 0.dx K

    I n the regi on i n quest i on, V = VQ = constant , E > o-y2 0

    Hence,

    >(i = Ae~qx+ BeqX,

    i s t he general sol ut i on. I fcwever, i l i(x=) = 0, requi r i ng B = 0,l eavi ng

    * = Aeqx,

    as t he wavef unct i on.

    5-28

    Si nce * i s real , the probabi l i t y densi t y P i s

    P = = i 2 = A2e- 2qX.

    Recal l i ng t hat x i s measured f ran the cent er of the bi ndi ngregi on, the suggested cr i t er i on f or D gi ves

    A2e- 2q(%a) _ e- l A2e- 2q( W(

    e- qa - 2qD = p- aq - 1

    D 1 - - - - - - - ts- - - - -

    ** 2{2m(V0 - E)}*

    w iUse t he scheme suggest ed i n Probl em5-26:

    E = Ex + ' / Wydx,

    i n whi ch E. and are ei genval ue and ei genf unct i on of the l owestenergy state of the i nf i ni te, f l at , square wel l potent i al . Fran

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    \

    Exampl e 5- 9, 10 the t i me- i ndependent part of i s

    Hence,

    ^ = (-) cos (i tx/a).a

    /i *Vi|ax = jc o s 2(irx/a ) VQcos (irx/a ) dx = - ^jc o s 3 (nx/a)dx.

    3 %/ Wpf l x = - Mcos udu = -j j -.

    E _ 2 2 a**

    5- 32

    The wavef unct i ons i n quest i on are

    Vx = (| )%oos(i rx/a)e- i E, t/ >1s *2 = (|)' ssl n( 2/ a) e_1E!t/ >',

    wi t h E2 = 4E1> The l i near combi nat i on i s

    V =

    Normal i zi ng thi s l ast gi ves

    v = o1v1 + c2y2.

    1 = / *dx,

    c J / TJ dx + c2c*/ Y*Y2dx + c ' c ^^d x + cc 1/ | 1

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    (a) The total energy i s E = p2/ 2m+ V. But V = 0 i n t he regi onof not i on, so that

    Hence,

    * = - + C2y2 , ' ^ (Ci y 1 + C2Y2 ,d x -

    a ^/ a x 2 = - ( f ) \ ; a2v2 /a x2 = -< ? f ) 2vr

    Al so, by Probl em5-32, / Y*Y2dx = / Y^dx = 0 and theref ore

    E = ( ( f ) 2c1c*/*' )' i dx + ( ) 2/ *V2dx},

    E - c c , L t c c * ^' H 9__2 + 2 2 2 2ma ma

    I = c1c*E1 + c2c *2E2.

    But

    (b) Si nce Cj C* + c2c* = 1,

    E = (1 - c2c*) El + c2c*E2 = Ex + c2c*(E2 - E1) .

    Wi th 0 < c2c* < 1, thi s means that

    E l < E < E2.

    Hence, i f the part i cl e can be f ound ei t her i n l evel 1 or 2,maki ng t ransi t i ons between than, i t s average energy, as woul d beexpected, l i es between the energi es of t he t o l evel s.

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    (a)' Hi e probabi l i t y densi t y V*Y has a t i me dependence of

    e - i ( E2 - E, ) t / H

    and theref ore the f requency i s

    v = (E2 - E / h.

    E = L td = J jL , ____________(6. 626 x 10~3V

    But,

    1 2ma2 8ma2 8(1. 67 x 10~27) (10_1V (1. 602 x 10- 13) '

    Ex = 2. 051 MeV; E2 = 4E;L= 8. 204 MeV.

    Hence,

    V C 8 J 04 - 2. 051 = 1 4 8 8 X i 021

    4. 136 x 10 X

    (b) The f requency of the phot on i s the same as i n ( a) . Hi e

    photon' s energy i s

    hv = 8. 204 - 2. 051 = 6. 153 MeV.

    (c) Photons wi t h thi s energy l i e i n the ganma- ray regi on of t hespect rum.

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    CHAFTED SI X

    Amnme that

    : Ce- l k , x

    bA*

    -----------

    *2 =Ae' 1* 2* + Bei J

    wtmre A = ampl i t ude of i nci dent - - - - - - - - -ynw, B = ampl i t ude of ref l ected J

    wnvr, C = anpl i t ude of theI i nnmi t t ed wave. There i s no wave movi ng i n t he +x- di rect i onI n reqi on I . Al so, i

    k .(M il k - i ^ v rki - >i * 2 - - - - - - - if

    nmt i nui t y of wavef unct i on and der i vat i ve at x = 0 i mpl y

    A + B = C, - k ^ + k2B = - kj C.

    ' Hi ene equat i ons may be sol ved t o gi ve the ref l ect i on and theI rnnsni ssi on ampl i t udes i n terms of t he i nci dent ampl i tude, thesui ts bei ng:

    k2 ~ kl

    k2 + kl

    2kA, C

    k2 +k lA.

    ref l ect i on coef f i ci ent F and t ransmi ssi on coef f i ci ent T nowl cane

    R . S I . S * - . ( ?LB2. ,k l k2. 2A*A

    'kl + k2

    vxC*C

    V A*A

    Hk 2k ,f__k\ I- - - - \ *

    W kl + k2

    4kl k2_

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    6- 5r a t r B B

    *r egi on 1 r r gi no 2 r cgi ns 3

    - - - - - - - - - - - - - - - - - - -

    (a) Assumi ng a wave i nci dent f r an the l ef t:

    regi on I s * Ae1* 1* + Be' i kx, = (2mE)

    regi on 2: * = Fe- kj X + Ge*2*, k2 = {2m(VQ - E) }V#;

    regi on 3: i(i = Ce*k, x + De ^ l X, t ut D = 0 si nce there exi st sonl y a wave movi ng t o ther i qht i n thi s regi on.

    Cont i nui t y of t he wavef unct i on at x = 0 and x = a requi re that:

    A + B = F + G, (i )

    Fe k2a + cek2a - ce* ' 3, (i i )

    Cont i nui t y of d i /dx at t hese same poi nt s yi el ds

    i kj A - i kj B = - kj F + k2G, (i i i )

    - k2Fe"k?a + k2Gek2a = i k1Cei k, a. (i v)

    (b) Frcm (i ) , A + B - G = F;

    Fran ( i i ) , (A + B - G) e_kza + Gekza = Ce ^3,

    Ae' k2a + Bek2a + G( ek2a - e' k2a) = Ce1*5'3. (i i *)

    Fr om (i i i ), Ai kx - Bi kj = - k2(A + B - G) + kj G,

    A( i k^+ k2) + B( k2 - i k^ - 2(3c2. (i l i a)

    - k2e' k2a(A + B - G) + Gk2ek2a = i kJCei ki a,

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    -Rk2e~kia - k2Be~k,a+ Gk2

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    Hence, the t ransni ssi on coef f i ci ent i s

    Vj C*C - 4i ( k1A 2)ei ki a 4i (k]/ k2)el k, a

    T = = q* V ksa - q2ekj a - q*2ekj a + q2*** '

    T = 16(k1A 2)2( q V 2(ek2a - e k2a)2 - (q2 - q*2)2}"1,

    T = 16(k1A 2) 2{( l + k2/ k2)2 (ek2a - e"k2a)2 + 16 ( k ^) 2}"1.

    T = {1 + - - - - - i V ( e k2a - e k2a)2} 1.

    Fi nal l y,

    so t hat

    16 (k1/ k2)

    ,kl ) 2 E . 2 2 V0(k2 " VQ - E' 1 + 1 2 " VQ - E'

    V?/ ( V - E) 2 . . , ,

    T = (I + -2___P ____ (p 2a - e 2 1 1T U + 16E/ (VQ - E) , e e > '

    (pk;a _ p_k2ai 2 _iT = {1 + E e ' >

    16 f-a - f-)vo vo

    6-6

    I f k2a 1, then ekza e k2a and the t ransmi ssi on coef f i ci entbeccmes, under t hese ci rcumst ances,

    T {1 +------jT - } _ 1 .

    16

    Now 0 < EA' o < 1 and theref ore

    16 | - 4,

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    Si nce, i n f act, i t i s assumed t hat kj a 1,

    2k2a

    16%11- f 1,

    and theref ore, under these condi t i ons,

    T = 16 #- ( 1 - r f j e"2*3.

    6-7

    Regi on 1:

    regi on 2:

    regi on 3:

    tatrgB-f-

    * = Ae1* 1* + Be- i k>x,

    * = Fei k>x + Ge- l k, x,ik ,x

    * = Ce

    I n these equat i ons,

    kx = (2mE) '>/)(, k3 = {2m( E - VQ) }*/ #.

    (a) Cont i nui t y of t he wavef unct i on at x = 0 and x = a gi ves

    A + B = F + G,

    Fe',1k, . + gg- i kj a Ce'l k , a

    Cont i nui t y of di(i /dx at x = 0 and x = a gi ves

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    l k A - l k B = l kj F - I Xj G,

    Fi k3ei ksa - i k3Ge"i l Csa = U Ce1* 13.

    (b) These are t he same as t he correspondi ng expressi ons I nProbl em6- 5, i f i n t he l at t er k2 i s r epl aced wi t h - i kj . Maki ngthi s al t erat i on i n t he expressi on f or T i n Probl em6- 5 yi el dsf or t he new t ransmi ssi on coef f i ci ent ,

    T ={1- - e- Vr1.i 6

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    (a)vo = 4i r 0 ? = ( 9 x 1q9) ' 6 J -U M 1 - 6 x 102 x 10- 15

    . ...6, 912 X 10~]3 J . 4 32

    1. 6 x 10 J / MeV

    (b) E = l OkT = (10)(1. 38 x 10~23)(107) = 1. 38 X 10' 15 J =

    8. 625 X 10~3 MeV = 0. 002VQ.

    (c) Numeri cal l y, a = 2r' - r* = 2 x 10- 15 m; al so,

    P E / {2m( V- E) }

    16 ^ (1 " = -032' k23 = - - - - > ^ ~a = 0. 91.

    T = {1 + &i 84..- ..0- 40.3?2}- 1 . 0 . 0 0 7 3 .

    (d) Hi e actual bar r i er can be

    consi dered as a ser i es of

    barri ers, each of const ant

    hei qht t ut the hei qht s decreasi ng

    wi th r; hence V - E di mi ni shes

    wi th r and t he probabi l i t y of

    penet rat i on i s areater than f oran equal wi dt h bar r i er of

    const ant hei ght V,O'

    fc l5/K

    1-l

    rtj ' o* 3

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    (a) Assumi ng a wave i nci dent f r an t he l ef t , t he wavef unct i on i nthe i ndi cat ed regi ons wi l l be

    regi on I s \|>= Ael kx + Be- l kl X,

    regi on 2 s * = Fe~i kj X + Ge1* 2*,

    regi cn 3 s ip= Cei kl X.

    The expressi ons f or t he k' s are

    / {2m( E - V0)}/)4, k2 = / (2mE)/7i .

    The equat i ons f or the wavef unct i on are i dent i cal wi t h t hose i nProbl em6- 5 i f i n t he l at t er k2 i s r epl aced wi t h i kj (note t he

    di f f erent expressi ons f or t he k' s i n t he tvro probl ems, hcwever)Usi ng Tl k kj ) f ran Probl em6- 5 and maki ng t he change gi ves

    T . {1 . . (. ** . e- 1* 3)2) ' 1.16( kj / k2>

    But,

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    These are f our equat i ons f or t he f i ve ampl i t udes A, B, F, G, C.Sol vi ng rel at i ve t o C gi ves

    k kA/ C = ei k!a{cosk2a - %i + ) s i nk2a},

    kO 1 I V aB/ C Wf c * - r-=) e 1 si nk. a,

    kl 2 l

    F/ C = >sei ( k>+k ) a,2

    G/ C = lsei ( ki_l c2) a(l + i ) .2

    The t ransmi ssi on coef f i ci ent i s T = C*C/ A*A. Subst i t ut i on ofthe appropr i ate ampl i t udes gi ven yi el ds the same expressi on for

    T cis obt ai ned above. ,

    (b) I n or der that T = 1 i t i s requi red t hat si n k a = 0 whi chI n turn requi res

    k2a = nn, n = 1, 2, 3, . . . .

    I n terms of t he par t i cl e energy E, thi s i s

    a = nn.

    2 2,.:- n * *E = ^ 2.

    2ma

    (c) I n the regi on of t he wel l , t hat i s, i n regi on 2, theprobabi l i t y densi t y i s

    = (F*ei ksX + G- e' * 2*) (Fe- i k!X + Gei kj X) ,

    k k*il/2 = C*C{~| + (1 - - | ) cos2k2(a - x)},

    k 2 k 2

    eval uated by usi ng t he F, G ampl i t udes f ound i n (a) . Theosci l l atory par t of t hi s probabi l i t y densi t y has a maxi mi mat

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    x = a. I f kj a = nir, i t al so has a maxi i mmat x = 0. I hi s

    i mpl i es t hat an i ntegral number of hal f rwavel engths f i t abovet he wel l ; i . e. , that

    a = n X2/ 2;

    but thi s i s equi val ent t o

    k-,a = nn,

    as obt ai ned i n (b).(d) One exampl e of an opt i cal anal ogue i s t hi n f i l mi nter f erenceas i n the opt i cal coat i ng of l enses.

    6- 17

    Numeri cal l y a = 2( 4 x 10- 10 m) and K = 0. 7 eV. E = K + VQ where

    nf l n2___________(6. 626 x 10~3V ___________#

    8ma2 8( 9. 11 x 10- 31) (8 X 10~10) 2(1. 6 x 10- 19)'

    E = n2 (0. 588 eV) .

    Set n = 1; then

    Ex = 0. 588 ev < K,

    whi ch i s not possi bl e. Usi ng n = 2 gi ves

    E2 = 22E1 = 2. 352 ev, |

    VQ = E - K = 1. 65 eV.

    The el ect ron i s too energet i c f or onl y hal f i t s wavel engt h t of i t i nt o the wel l ; t hi s may be ver i f i ed by cal cul at i ng thedeBrogl i e wavel engt h of an el ect ron wi t h a ki net i c ener gy overthe wel l of 2. 35 eV.

    6- 18

    tfkx = (2rr(V0)%, Xk2 = {2m(9V0)}%; J i kj = {2m(4V())}!l;

    These rel at i ons can be summari zed as

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    regi on 1 r r gi nn 3

    - - - - - - - -oc.

    Theref ore,

    kx = k, k2 = 3k, k3 = 2k.

    = Aei kx + Be_i kx,

    *2 = Fe- 3i kx + Ge3i kx,

    = Ce'2i kx

    Matchi ng ^ and d*/ dx at x = 0 gi ves

    A + B = F + G,

    A - B = 3( G - F) .

    At x = a t he same ccti di t i ons yi el d

    Fe- 31te + Ge3i ka = Ce2i ka,

    Wr i t i ng

    - 3Fe- 3i t e + 3Ge3i ka = 2Ce2i ka.

    i ka

    these l ast equat i ons bcccme

    - 1 1 ?Fz + Gz = Cz ,

    - 3Fz- 3 + 3Gz3 = 2Cz2.

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    I n terms of C, the transni t t ed wave ampl i tude, the sol ut i ons are

    . _ 10 - z6 cA 6z C'

    B - 2g6 ~ 5 CB 6z C'

    F = I Z5C,

    The desi red t ransmi ssi on probabi l i t y i s

    V A*A (Kk1)A*A A*A"

    C*C = ( ~ A * ) ( SS- g. A) - - - - - - - - 2 ^2 - - - - ^ A*A.10 - z* 10 - z (10 - z*6) (10 - z )

    ^ z*z = e - ^ = I ;

    (10 - z*6) (10 - z6) = 100 - 10(e_6i ka + e6i ka) + 1,

    (10 - z*6) (10 - z6) = 101 - 20cos6ka.

    Hence,

    72T = 101 - 20cos6ka

    6-20

    (a) I n t he l owest energy st ate n = 1, >|i has no nodes. Hence

    must cor respond t o n = 2, ^ t o n = 3. Si nce Efi n2 and Ej =

    4 ev,

    Ej j / Ej = 32/ 22; EI I = 9 eV.

    (b) By the same anal ysi s,

    Eo/Kj = l 2/22, Eq - 1 ev.

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    (a) The energy i n quest i on i s

    n2 * ^.2'

    2maEn = n

    and theref ore t he energy of t he adj acent l evel i s

    bo that

    n _ En+1 ~ En _ (n + l )2 - n2 _ 2n + 1

    En " En n2 n2 *

    (b) I n t he cl assi cal l i mi t n * ; t ut

    Ur n ^ = Li m * 1 = 0,rt* n n

    meani ng that the energy l evel s get so cl ose toget her as to bei ndi st i ngui shabl e. Hence, quant umef f ect s ar e not apparent .

    6-24

    The ei genf unct i ons f or odd n are

    i|in = Bncos( nnx/ a).

    For normal i zat i on,

    r%a j -nn/2

    1 = J>2dx = B2 \c o s 2 (nnx/a)dx = 2B2 (a/ ntt )lcos 2u du,

    J - %a J O

    1 = 2B2(a/ nn)(nn/ 4) = B2,

    Bn = 4

    f or al l odd n and, theref ore, f or n = 3.

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    By vi r t ue of Probl em6-24, t he normal i zed ei genf unct i ons are

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    2 2Thi s i ncreases sharpl y wi t h n si nce E 5-ija

    t he i nt egrand bei ng an even f unct i on of u.

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    The Schrodi nger equat i on i n t hree rect angul ar coordi nates i s

    -2. . 2. .2.

    ax 3y 3z K

    I nsi de the cubi cal regi on where V = 0,

    a! | + + | + ^ = 0 .

    3x 3y 3z K

    Assume that

    (*yz) = X(x)Y(y)Z(z) .

    Then, i f ' denot es the der i vat i ve of a f unct i on wi t h respect t oi t s i ndependent var i abl e,

    + T + + = ' (*>

    Thi s gi ves

    = - k2; X = Asi n (kxx) + Bcos (k x),

    kx = real constant . Si mi l ar l y

    Y = Csi nl kyY) + Dcos (k y) ; Z = Esi n( kzz) + Fcos( kzz).

    Al so, f r an (*),

    kx + *y + kz = W -

    Si nce V = out si de the cubi cal regi on, >Ji = 0 at t he boundary:

    0 = X(0) = Y (0) = Z (0) + B = D = F = 0;

    0 - X(a) = Y(a) = Z(a) -* kxa - nxn, k a = i yr k^a =

    wi t h = 1, 2, 3, . . . . Hence

    ^ = (CAE) si n (nxi rx/a) si n (nyi ry/a) si n (nzi i z/a),

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    (a) Let M = mass of wi ng. Hi e zero-FOi nt energy i s

    EQ = (0 + %)Ko) = y w = h/ 2T,

    T = per i od of osci l l at i on. The actual energy of osci l l at i on i s

    E = yt A2 = Ij mA 2 = 2h2MA2/ T2.

    Thus, the val ue of M at whi ch E = EQ i s

    M = M . (6. 626 x i O- Ul I . l j 68 x 10- 33 kg.A-A-K*-

    I Ms i s l ess than the mass of an el ectron. Hence E E. and

    the observed vi brat i on i s not the zero- poi nt mot i on.(b) Cl ear l y then, n 1 and theref ore

    E = nhv - 2tt2MA2/ T2 * n = 2n2M&2/hT.

    As an exampl e, take M = 2000 kg:

    n 2, 2(2000).(.C i l l _ 6 x 1035>

    (6. 626 x 10 ) (1)

    6-30

    The zero- poi nt energy i s

    Eq = Wu = W(C/ ta)%.

    Theref ore,

    E_ = |i (l .055 x 10- 34) (--- 1C|3 o'fi) t l . 6 x 10- 19) "1,0 4. 1 x 10 1:6

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    (a) Usi ng Efl = 0. 051 eV, t he l evel spaci ng wi l l be

    AE = A(n + (rtHu = Ho = 0. 102 eV = 2EQ.

    (b) The energy 1of the photon = AE = 0. 102 eV.

    (c) For t he photon,

    1 - V

    But

    = AE = Ho,

    ph ID,

    wher e u = cl assi cal osci l l at i on f requency. Unas,

    v = 1 . .(0.-.102) .(1. 6 X 10- 19) _ 2- 5 x 1013Hz-

    (6. 626 x 10~39)

    (d) Photons of thi s f requency ar e i n t he i nf rared spect nm,X = 12, 000 nm.

    6- 32

    (a)

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    CHAPI TK SEVEN

    Tl i e t i me- dependent equat i on i s

    Let

    y(x, y, z, t ) = \ p(x, y, z)T(t ) .

    Put t i ng thi s i nt o the f i r st equat i on gi ves

    - T( t) ( | + 2! | + a! | ) + v(x, y, z)*(x, y, z)T( t ) = i # f,3x 3y 3z

    assumi ng that V does not depend on t expl i ci t l y. Di vi di ng theabove by t he wave f unct i on yi el ds

    - i * v2* + v - * t f = = E-

    TTi ere are two equat i ons:

    V2* + %( E - V)4* = 0,P

    f or t he space dependent part of t he wave f uncti on, and

    i M

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    The reduced mass i s

    mnucme m-nuc e /, e x

    si nce each nucl eus t o be consi dered i s sur rounded by oneel ect ron. The charges and masses of t he nucl ei are

    mH = mp; "b = anp; "fee = * V h m = l ! ZHe =2'

    mp = pr oton mass. The mass rel at i ons are approxi mate. Si nce

    me 11836'

    i t f ol l cws that

    *H(1)2 = V 1 - IS6>(1)2 = - " 95V -

    *D(1)2 = me{1 - 2( l i 36r}(1)2 = - 9997me;

    Ee WHe( 2)2 " 3-9995n,e-

    These gi ve t he rat i os:

    Ej j/ Ej, = 1. 0002; E / E^ = 4. 0015.

    7- 7

    (a) Si nce R21 = re~r/,2a, P( r) = 4aQ.

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    (a) The potent i al energy and the ground st ate wave f unct i on are

    V = - e2/ 4*e0r, ^ = t f ^3/ V r / a\

    Theref ore,

    rT\ f2ir

    liT *

    e- r / a o r 2si nedr ded$ ;

    V _____ - 2-- fxe~xdx ______

    4i *oao\0 4lieoao'

    (b) I n the ground state.

    E = - ue4/ (4nc0)22X2.

    Si nce aQ = 4ne0H2/ ue2,

    V = -2- - - ye' = 2E; E = IjV.

    (4nG0) 2H

    (c) As f or the ki net i c energy,

    E = K + V; E = K + V; = K +V; K = -%V.

    7- 9

    (a) For t he st ate wi t h = 0,

    *210 4 ^o 3/ 2( r / aO)e"r / 2a0cos6

    4

    so that

    v?i n - - - - - - - - - - - - - \ ( r3/ a2) e' r / aocos2esi nedrde

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    V2 1 0 - - - - - - 3g-2 - a2[x3e~xdx- (*)

    210 24a0 J o

    For t he l i mi t s on r,0,i ti see Probl em7- 8. New,

    fJ ox3e' xdx = 6,so that

    e2 1 e4- - - - - - - - - - - - - - - - - - - 2E- .210 4"E0a0 22 (4ne0) W 2

    For t he states wi t h m = t l :

    and theref ore

    V2i +i - - - - - - - f"---14e"r / asi n30dr d6d*,- 64, a3(4, Eo) J a2

    V2l l l = - 24a0We 0)]X e dx

    Thi s i s t he same as (*) above. Hence, regardl ess of t he val ue of

    VV2i = 2E2.

    (b) I n t he case of I = 0,

    *200 = 4 7 i W a- 3/ 2

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    V20 = - 8 5 ^ o i (2 - *> dx - - 8 3 ^ T (2>= 2E2-

    (c) These resul t s ar e expected si nce, wi t h V r- \ t he averaqepotent i al energy seen by t he el ect ron i s t he same f or al l n = 2states, regardl ess of I. Thus, the expect at i on val ue of anenergy wi l l be the same f or these states.

    7-10

    R(r) must sat i sf y Eq. 7- 17:

    - + + [ ( E - V) R = III + 1)- .dr M r

    I f R = r1,

    dR ___d r " " 1 ' dr 2

    Subst i t ut i ng t hese i nt o the radi al equat i on gi ves

    III + Dr 1- 2 + {Er 8, - Vr*} I III + l l r1' 2.H2

    Now E i s a const ant i ndependent of r, and V = k/ r; thus the tvo

    terms i n {} ar e proport i onal t o r*, r*- 1. As r approaches zero,

    r*- 2 r', r*- 1; hence, {} * 0, and t he equat i on i s sat i sf i ed.

    7-11

    (a) Tt avoi d i nf i ni t i es, i ntegrat e radi al l y t o a f i ni t e l i mi t R:

    rR /-6

    P =4ttR

    r ri [dv = -I I 2nr2si n0drde = Ml - cose) ,

    R-V3* 4"R J r=cJ 6=0

    P(23. 5) = 4. 147%.

    (b) For t hi s state:

    *210 = 4 7 ^ 0 5/ 2re' r / 2a0cOs6-

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    Si nce thi s i s al ready normal i zed.

    P = J >2dV = -]6Y2-T,)a~5| [r2e' r / acos20r2si n0drd8.

    ' 0J0

    P = %(1 - cos30),

    -P(23.5) = 11. 44%.

    2=12

    (a) See sketch, f ol l owi ng page.

    (b) P (3cos20- l ) 2; hence P j ^= 0 at cos0 = i l / / 3, gi vi ng

    9 = 54. 7 , 125. 3.

    (c)Pnax = 4 (6 = 0- ),

    i Pmax = ^

    (3c o s 26 - 1 ) 2 = 1 ,

    3cos26 - 1 = l l ,

    e = 35. 3", 90, 144. 7.

    7-14

    Let (3,2, -1) represent ip(n=3,11=2,m l ) ; (2, 0, 0)* represent

    (n=2 , a=0 ,ma=0 ) etc. I ti en i t i s requi red to stowthat

    = f { ( 3 , 0 , 0 ) * ( 3 , 0 , 0 ) + ( 3 , 1 , 0 ) * ( 3 , 1 , 0 ) + ( 3 , 1 , -1 ) * ( 3 , 1 , - 1 )

    + (3, 1, 1)*(3, 1, 1) + (3,2,0) * (3,2,0) + (3, 2, 1)* (3,2,1)

    + (3, 2, 1)*(3, 2, -1) + (3, 2, 2)*(3, 2, 2) + (3, 2, - 2)*(3, 2, - 2)}

    i s i ndependent of 0, $. Now

    (3, 2, -2)*(3, 2, -2) = (3, 2, 2)*(3, 2, 2),

    (3, 2, - l )*(3, 2, - l ) - (3, 2, 1)*(3, 2, 1),

    (3,1, -1) *(3, 1, -1) - (3, 1, 1) *(3, 1, 1),

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    *5*3 = | {3, 0, 0)*(3, 0, 0) + (3, 1, 0)*(3, 1, 0) + 2(3, 1>1)*(3, 1, 1)

    + (3, 2, 0)(3, 2, 0) + 2(3, 2, 1) *(3, 2, 1) + 2(3, 2, 2)*(3, 2, 2) }.

    Mow subst i t ute t he speci f i c expressi ons f or t he var i ouswavef unct i ons appear i ng i n the above.

    I = 2 t erms:

    i ndependent of e,i j>. The i = 0 terms depend on r onl y. Thus, al l

    terms i n have been account ed f or and thei r sumf ound to be

    i ndependent of di recti on, so t hat 41* ^ i s spheri cal l y

    syi met r i c si nce i t depends on r onl y.

    7- 16

    2{(3, 2, 1)*(3, 2, 1) + (3, 2, 2)*(3, 2, 2)} =

    2 (8 1) 2ira

    (3, 2, 0)*(3, 2, 0) - - - - - r4e' 2r/3a

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    Theref ore,

    Lx, opt 21- l = HR - % E - v>Rr 2}.V1

    37(r2 9r' + U* - 2

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    (a) Si nce

    Pop - - ! ? * = ei kx'

    Pop' 11= f r ~ (' i >') UWe 11" = #**.

    and thus t he ei genval ue' i s Kk.1kx

    (b) Usi ng * = e , r epl ace k i n (a) wi t h - k t o get theei genval ue ->0c.

    (c) These resul t s i ndi cate that measurement s of rrcmentun wi l lyi el d Jflc preci sel y.

    (d) \p = si nkx, coskx ar e not ei genf unct i ons si nce 3/ 3x convert ssi ne t o cosi ne and cosi ne t o si ne.

    (e) These states, not bei ng ei genf unct i ons of t he moment umoperator , wi l l not yi el d preci se val ues of t he remant un uponmeasurement .

    7-20

    (a) Wi t h R a const ant and V = 0, t he total energy E i s

    E = K + V = K.

    But t he ki net i c energy K i s si mpl y

    K = !jlu)2 - I j l (L/ I )2 - L2/ 2I ,

    where I = rotat i onal i ner t i a akcut t he z-axi s. Hence

    E = K = L2/ 2I .

    ( b ) 2

    Lop = Lz, op- - i 1l*'-

    Eop = f t

    Al so, = y (r,e,

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    Let *)T(t).

    Subst i tute thi s i nto t he energy equat i on of Probl em7- 20(b) anddi vi de by to obtai n

    l i! T * . _ l *i i df * _ i Mi _ E

    21 V * 21 * d *2 T d t

    where E i s the separat i on const ant . Thus two equati ons emerge:

    d2t

    d$2and

    (b) f = T = -fT.

    7-22

    (a) Fr an the precedi ng probl em,

    5 E - _ i E _ _ . i E dt . T _ e- i Et / Kdt H T; T " n dt, T - e

    The normal i zat i on const ant wi l l be i ncorporated i nto $.

    (b) The sol ut i on above represent s an osci l l at i on of f requencyoi gi ven by

    E - fa.

    But thi s i s the de Brogl i e- El nstei n rel at i on. Hence E i s t hetotal energy.

    7-23

    The equat i on f or i s, f ran Probl em7- 21(a) :

    d2 -

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    Thi s i s anal ogous t o the cl assi cal si npl e harmoni c osci l l at orequat i on:

    d2x 2 ~ + (i) x = 0 .dt

    The canpl ex f orms of t he sol ut i on wi l l t heref ore be

    * = ce1*1+ c*e_l m>, m = / (2I E) / H.

    7- 24

    (a) The par t i cul ar sol ut i on bei ng consi dered i s

    t =e1*1= cos (m)>) + i 8i n(m)i ).

    Si ngl e- val uedness requi res that

    4i(0) = 4(2n) 1 = cos(2i roi ) + i si n( 2nm).

    Hence,

    si n(2i tm) = 0 ; cos( 2nm) = 1 ; m = 0, 1, 2, . . .

    (b) By Probl em7-23

    * - * , . - 0 . 11 . ! ! . . . .

    (c) Sol vi ng t he probl emvi a the ol d quant umt heory gi ves

    E _ L2 _ (nH)2 n h 221 21 rT' n l * 2' 3'

    Evi dent l y t he new versi on, i n cont rast t o t he ol d theory,i nt roduces an m = 0 (E = 0) state; al so, t he exci t ed l evel s arenow t wo- f ol d degenerate.

    (d) Apparent l y there i s no roomf or zero- poi nt energy si nce Ri s assumed constant . I n actual i t y, t he masses, on a mi croscopi cscal e, wDul d be aterns whi ch osci l l at e sl i ght l y, so that I)cannot be assumed t o be f i xed.

    7- 25

    The compl ete wave f unct i on i s, f ran t he precedi ng probl ems,

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    The wavef unct i on must be normal i zed at any t i me t: thus,

    = 1,

    1 = j (N*e- i m* ) ( Ne* ) ^ = N*N(2n) ,

    N * N =i

    7- 23

    Use * = M ' V * 1; Lz = - i *

    (a)2 t t f 2 iT f 2 iT

    (b)

    f= U*( - :Jo JO

    L = m>(.

    Al so, f ran (a)

    L = mV .

    Si nce L2 = L2, measurement s of L wi l l yi el d mtf exactl y.

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    CHAPTER EI GHT

    (a) I t t he area of t he el l i pse be A; then,

    U* = i A = | A,

    T t he per i od of revol ut i on. The angul ar moment umi s L = mr 2de/ dt>

    al so, dA = >ir2de, so that

    t _ dA _ . Adt " t '

    si nce dA/ dt equal s a const ant i n cl assi cal mechani cs i f thef orce i s cent ral . Theref ore,

    _ e Ur = aL. &_ _ e_HI T 2m 2m' L 2m

    (b) Thi s r esul t i s i dent i cal to Bq. 8- 5, der i ved assumi ng a

    ci r cul ar orbi t .

    8- 4

    The f i r st apparatus produces t wo beams, one wi t h spi n paral l el(i n quant ummechani cal terms) t o t he di rect i on of t he f i el d ( +z),t he ot her wi t h spi n ant i paral l el . Thi s l at t er beami s bl ocked byt he f i r st di aphra n. Hence, a "pol ar i zed beamof at oms enterthe second apparatus, f i el d di rect i on +z . Thi s second magnet

    produces a new space quant i zat i on al ong z . I n anal ogy wi t h thepassi ng of pol ar i zed l i ght through P olaro id (except t hat theangl e f or no t ransmi ssi on i s 90 i n t he opt i cal case, 180* i nthe at omi c) , t he second magnet al l ows onl y the proj ect i on of theent er i ng spi ns al ong +z (not - z ) t o pass. Thus, i f I 1 i s t hei nt ensi t y of t he beament er i ng t he second apparatus and I t hei nt ensi t y of t he unpol ar i zed beament er i ng the f i rst ,

    I = %!(! + cosa) = W0(l + cosa) .

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    8 -5

    The def l ect i ng f orce i s

    F = uzdBz/ dz,

    where

    W s '

    si nce = 0. I f D i s the def l ect i on and F i s constant ,

    D = tet2 = !s(F/m) (L/v)2,

    L = l ength of maqnet and v = speed of t he atoms. Thus,

    D = * 5 (dBz/dz) (L/ v)2;

    gs b s

    For atoms emi t ted f romt he oven, Ijniv2 = 2kT wi t h T = 1233 K.

    Hence,

    f z _ 8KTO = 8( 1. 381 x 10~23) (1233) (0. 0005) = ^ T/ m_

    62 'LW s (0 5)2(2) (9. 27 X 10- 24) (Is)

    8 -6

    (a) The orbi t and spi n enerai es are

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    Thus t he onecay l evel di agr amappear s as f ol l ows:

    m m EX s

    - - - - - I

    ^ 0

    \ l

    - - 1

    \ l

    _- 0

    1 +% +2

    0 +%-+1 tvi o- fol d deg.

    B = 0 ^ r 0 two- f ol d deg.

    0

    * } - i-h J

    - 1 t wo- f ol d deg.0

    - 1 ~h - 2

    (c) The naxi j numseparat i on i s

    max " 4bB = 10*2 ev-

    4(9. 27 x 10- 24)B = (10. 2) (1. 6 x 10- 19),

    B = 4. 4 X 104 T.

    8-8

    Si nce I,j > 0 and s = *s t he rel at i on

    / { j t j + i d > \Aia+ d ) - /{s(s + i)> |,

    becomes

    j ( j + 1) > H I + 1) + | - / {3UI + 1)}.

    (i) I = 0. I n thi s cas^ (A) reduces t o

    j (j + 1) > 3/ 4.

    But f or *. = 0, j = % (the onl y possi bi l i t y) , so t hat t herel at i on i n quest i on i s sat i sf i ed.

    (A)

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    (i i ) *. * 0. (a) j = 8, + %. Put t i ng thi s i nt o (A) gi ves

    whi ch cl ear l y i s sat i sf i ed f or al l I > 0.

    (b) j = I - Vn, n = 1, 3, 5, . . . Put t i ng thi s i nto (a) yi el ds

    n = 1 (B) becomes

    0 < (2 - 1) ( + 1),

    whi ch i s sat i sf i ed f or I > % (i . e. , j > 0) , so the rel at i on i sobeyed here al so.

    n = 3 I n thi s event , (B) gi ves

    Evi dent l y thi s i s not sat i sf i ed f or I > V, < 0, but i s for0 0.

    Resul t s si mi l ar t o the l ast appl y t o n = 7, 9, . . . etc. Hence,si nce j > 0 the i nequal i t y i s r est r i cted t o the val ues of jgi ven i n the probl em.

    > V{3( + 1)},

    -n + k(n2 - 2n - 3) > -{3. (. + 1)}. (B)

    0 < 38. (-28, + 1)

    0 < - 222 + 3 3 1 - 9

    0 < - 22j 2 - 77j - 64,

    8-10 /

    (a) Largest j = 4 + %= 9/ 2;l argest m. = j = 9/ 2. The

    L = / {( + 1)}K = / (20)tf,

    S = / {s( s + 1) }H = /3tf/2.

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    Appl y t he l aw of cosi nes t o the L, S, J t r i angl e:

    J 2 = L2 + S2 - 2LScos( 180* - 9),

    ^ = 20 + | + 2/ {20( | )}cos6 ,

    6 = cos_1 = 58. 91*.

    (b) Si nce u. i s ant i paral l el t o L and i s ant i paral l el t o 2, +

    t he anql e between u. , y = 58. 91".X s

    (c)

    COS* = f = i 9 ; * = 25. 24*.

    8-12

    Def i ne the rel at i vi st i c energy as

    Er ei = K + V.

    Now

    K = me2 - nv.c2 = nuc2{--- L- y- - 1},v 0 / ( I - 8 )

    B = v/ c. The rel at i vi st i c i ranentump i s

    2 -*sp = mv = m0ce -

    K V 2 ( p , 2 - ^ 4) 4 ' ^

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    and theref ore 2

    1 =*W - Ecl = ( ' ^ +V) - ( + VK

    I f p =pcl * then

    r el - - P4/ 8 c 2.

    Mow usi ng cl assi cal expressi ons, i n t he spi r i t of theapproxi mati on,

    | ^ + V = E; p4 = 4m2(E - V) 2,

    so thatFT - 2EV + v

    AE- 1 ---------------t o ? '

    Wi th E = const ant and V = - e2/ 4neg, t he above yi el ds the f i nal

    quoted resul t di rectl y.

    8-15

    (a) The i ntegral s t o exami ne are

    / (erj i pj dr; / ( er i dx.

    Si nce both are si ngl e el ect ron ei genf uncti ons, each has

    the form>l'nj ln = (n. l . m) . Hence each i ntegral may be wr i t ten

    e / ( n . f c . m^J d i .

    Now the par i t y of r i s odd: P(r) = - r; t he par i t y of (n.H. m)

    i s (l )a so that the par i t y of (n. f c. mMn. H. m) i s ( - I )2* and

    theref ore i s even regardl ess of whether SL i s odd or even. Thusthe par i ty of the i ntegrand above i s odJ , and the i ntegral over

    al l space vani shes.

    (b) El ect r i c di pol e i reroents const ant i n t i me do not exi st,si nce t he governi ng i ntegral above i s zero. Onl y i ntegral s

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    preceded by e" ** Ef^ , dependi ng on t i me, may be non- zero.

    8- 16

    For n = 2: SL= 0, m = 0; S. = 1, m = 1, 0, -1. Hence the

    i ntegral s t o be consi dered are

    (i ) / ( l , 0, 0, )*(er) (2, l , l )dr; (i i ) / (1, 0, 0)*(2, l , 0)drs

    ( i i i ) / ( l , 0, 0) *(er) (2, 0, 0)dT,

    where = (n, , ma). Al so,

    r = ( rsi nBsi n*) ! + (rsi n6cosi (i )] + rcosei c.

    Subst i t ut i ng t he expl i ci t expressi ons f or the wavef unct i onsgi ves the fol l owi ng f or t he i nt egral s above.

    (i )

    e/ e- r / a (r) e_r / 2a0ei 4'r2sin6drd6d

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    p . O , ^ V ^ d r * 0; j lcos28si n0d6 = j ^ 0 .

    Thus here al so / ( l , 0, 0) *( er ) ( 2, l , 0)dx ^ 0 and a t ransi t i on i sal l owed, agai n i n accord wi t h the sel ect i on r ul e si nce here41- 1.

    (i l l ) Fi nal l y, t hi s i ntegral gi ves

    e/ e~r / a (r) (2 - r / a0)er/'2ar2si nedrded41.

    The I , ] t erms vani sh f or t he same reason as i n ( i i ) . But thi st i me the 0 i ntegral i n the k termi s

    csi necosede = 0

    Thi s t i me, then, / ( l , 0, 0) * (er) ( 2, 0, 0) dT = 0 and the t ransi t i oni s f orbi dden. TTi e sel ect i on rul e i s obeyed si nce M. = 2 between

    t he t wo st at es and the sel ect i on rul e i s Ail = 1.

    8- 17

    I t i s desi red to check t he sel ect i on rul e An = i l by eval uat i ng

    X " el **f u*ni du * H nf u*ni du,

    si nce t[>(u) i s real and u x.

    (i ) nt = 3, nf = 0. I n t hi s case,

    I f (3u - 2u3)e_l !U e_l iU udu = 2 3u2 - du.

    I = 2{3( i m%) - 2( | nS} = 0.

    But An = 3, so t he sel ect i on rul e i s not vi ol ated,

    (i i ) nt = 2, nf = 0:

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    si nce t he I ntegrand i s of cxi J par i ty) i n - 2 i n thi s i nstance,

    (i i i ) n = 1, nf = 0.

    2I l uV " du = 2 (k ) ? 0,.p

    J0

    and An = 1.Thus t he sel ect i on rul e An i l i s obeyed i n these three cases.

    8-18

    (a) Fran EQ. 8- 43, t he t ransi t i on rate R i s

    R =i ! * y

    30hc

    wi t h

    3l Uoex( 1ax|2'J -CO

    V - ( C/ m) *5.

    The i nt egral i n the expressi on f or R i s, wi t h u = (On) x / ,

    ..2 _1_.2 u r , -.2

    P = 2eA0Ai yr ' i U"xue- ' i U dx = 2eAQA1

    The normal i zat i on const ant s Ap and A1 are det ermi ned f ran:

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    Sol vi ng these l ast f or AQ, t he expressi on f or P becomes

    Put t i ng thi s and the expressi on f or v i nt o R gi ves f i nal l y, f or

    8-19

    The i nf i ni t e square wel l ei genf unct i ons, apar t f romthe not -

    needed normal i zat i on const ant , are

    * (x) = si n

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    agai n si nce the i nt egrand i s odd.

    (i i i ) Transi t i ons bet ween an odd and an even- n l evel s

    rHn> r Hmp

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    New,

    r2ir r 2n r2nr r

    le in9de = lalo 'o

    coe(n6)d6 + i | si n(n0)d0 - ( si n2mi - i cos27i n + i ) .

    Hence, i f n = 1, 2, 3,

    r2"

    le n6de = 0.Jo

    On the ot her hand, i f n = 0, then

    r2n r2n

    j ei n6d0 = 30 - 2n.

    Thus, I x ^ 0 ral l y i f ei t her (i ) tm + 1 = 0, or (i i ) t o - 1 = 0;

    that i s, onl y i f Am= i l .

    Si nce

    s i n ^i f e ^- e ' 1*),

    I y = = { I i ( te+1)* - ei (ta- 1, *>d.

    The i ntegrand i s si mi l ar t o t he one f or I x - Theref ore, the

    sel ect i on rul e i s Am= i l .

    B-21

    By Bq. 8-43, 3 2

    R12 ' J12P12

    *01 uoi poi But Pf i depends onl y on Am; si nce Am= - mf = +1 f or bot h

    t ransi t i ons, P12 - PQ1- Hence,

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    * 01

    si nce v =* ( AE/ W. But ,

    Em

    and theref ore

    bim*01 o2

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    CHAPTER NI NE

    9-3

    nie probabi l i t y densi t i es are

    , 1 11*S*S = t 4>*(l)*|(2)A)B( l)*a(2)

    A AI I I I V

    1 #*,

    *k = V

    The same resul t i s achi eved i f , i nstead, par t i cl es 1 and 2, or2 and 3 are i nterchanged.

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    The ant i syi met r i c f unct i on f or t hree part i cl es i s

    a = TJ Tt Pa(1) (2) (3) + *B(l )*Y (2)*a (3) + *Y (l )+a (2)*e (3)

    - *Y (l)H-B(2)+a - *B( l )*a(2)*Y(3) - * a(l )*Y (2)*B(3)) .

    Upon f ormi na fVppp&t t here appears t he f ol l owi ng terms:

    (i ) Si x terms, each the square of those above; f or exarpl e,

    / * U) *g (2) ** (3)*a (1) *B (2) *Y (3) dt j ai j dTj

    = {J \| (1) *a (1) dTl ) {/ ** (2) (2) dr2) {/ ** (3) (3) * 3},

    = UM1H1} = 1,

    assumi nq t hat each wave f unct i on i s normal i zed. Hence, theseterms add t o 6.

    (i i ) Cr oss terms; f or exampl e,

    /

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    ''space = 7 2 ^ 100(1) *100121 + l OO '*' l00(1)

    =M (t )3/2e'2r,/a>(t ,3/2e'2r2/a0)-\(jgpi n must be ant i symmetr i c si nce the space f unct i on was chosen

    t o be symmet r i c (el ectrons i n the same l evel ) . The coul crrbenergy i s

    v4lt0 r12'

    where r 2 f ^ - r2 i s t he di st ance between the el ectrons. Thus

    V = /*JVi|'A'3T1dT2do1do2,

    i n whi ch Oya2 are t he spi n var i abl es. J fcwV i s i ndependent of

    the spi n of t he el ectrons, so t hat i f t he spi n wave f uncti on i snormal i zed, then

    V = Space space l a-

    Put t i ng i n t he wave f unct i on gi ves

    V = - ^- f e - 4( r>+ / a^ r 2dr 1r 2dr 2si nel si ne2d81de2d*1d$2,

    * a003 12

    i n whi ch r 12 = ( r ^r ^e ^, ^, ^) .

    ttowsuppose that t he ant i synmet r i c space f unct i on had beenchosen. Wi t h bot h el ectrons i n t he ground state, thi s wi l l be

    ' space = > 100(1I W 2) * *100(2)*100(1)) "

    I t may be concl uded then that wi t h both el ect rons i n the groundstate, t he el ectron spi n must be i n t he ant i synmet r i c (si ngl et)

    state. The coul onb i nteract i on, bei ng posi t i ve, wi l l i ncreasethe ground st at e energy over t hat cal cul ated by i gnor i ng i t.

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    Consi der tD ei genf unct i ons sol ut i ons of

    u2 A- , u2 d2*,

    - h - ^ 1 ( 1 > - | ; ^ r + v * i = E i * i -

    Take the canpl ex conj ugat e of (2) t o get

    vi2

    - f e ^ r + v* I - Ei

    (i ) I f Ej j* E^ and the systemi s bound, the wavef unct i cns

    approach zero at bot h i nf i ni t i es. Thus the i ntegral vani shes and

    Uj l dx = 0.

    (11) I n the ccnt i nui mregi on (unbound syst em) , t he wave f unct i onremai ns f i ni t e at l arge posi t i ve and negat i ve x. I n pract i ce,towever, box normal i zat i on i s i nvoked and t he wavef unct i onvani shes at the sur f ace of t he box, so t hat the resul t abovei s achi eved here al so.

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    (i i i ) I f Ej = (degenerate case) , const ruct

    a = V i + V j '

    al so a sol ut i on f or t hi s potent i al . I f a a. ar e chosen proper l y

    can be made orthogonal to

    J tyj l i j dx = 0 = a*/\pj \(i jdx + a*/ i ), * dx,

    a*f >f tpj dx + a< = 0,

    and so choose

    i j = " / *J *. j dx-

    9- 13

    - MWr ) |

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    where = ground st ate energy of t he hydrogen atan. Val ues of

    Z(r) may be taken (not easi l y) f r cmFi g. 9-11.

    (b) The resul t s are shown on t he precedi ng page. The f i rstthree l evel s of argon are

    I n t he ground stat e (n = 1) of hel i i m. Fi g. 9- 6 gi ves E. o -80 eVand theref ore 1

    (b) Wi t h so f ew el ectrons, i t i s not cl ear whet her an i j i ner or

    cut er shel l i s bei ng descr i bed. I f = n = 1 an out er shel l i s

    i ndi cated; f or an i nner shel l , Z1 =Z - 2 =2 - 2 =0 .

    (c) The f act t hat Z1 equal s (or r cughl y equal s) nei t her n = 1

    (outer shel l ) nor Z - 2 = 0 ( i nner shel l ) i mpl i es that the

    Hart ree met hod i s not appl i cabl e t o hel i un. Thi s i s not ver y

    surpr i si ng si nce a stat i st i cal met hod cannot be expected t owork wel l wi t h so f ew par t i cl es (two el ect rons) .

    E1= - 3500 eV; E2 = - 220 eV; = - 16 eV.

    9- 14

    (a) Bq. 9-27 i s, wi t h E^ ref er r i ng t o hydrogen.

    - 8 - Z ^ = - Z*(13. 6),

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    (a) Fr an Fi g. 9-6, Em , = +30 eV;coul

    E = 1 coul 4np r '

    30 = (9 x i oV 1-6 X - y ,r ( 1 .6 x 10

    coul

    r = 0. 048 nm.

    (b) E__ _ = +9 ev - r = 0. 16 nm.

    9- 17

    For the el ect ron r x p and t i s perpendi cul ar to the pl aneof t he orbi t . Now v / 0 anywhere i n the orbi t and theref orep # 0. I f L ^ 0, t hen r ^ 0everywhere and the el ect ron

    avoi ds the nucl eus (r = 0) . I fL = 0 , t he el ect ron voul d moveon a st rai ght l i ne t hrough thenucl eus.

    (a)

    E = K + V = - + V,

    E = + p!> + v -

    But L = rp (si nce r x p, = 0);hence.

    2'

    (b) I n one di mensi on ^ = 0, L= 0 and E - Pj / 2m+ V1. Thi s and

    the precedi ng equat i on are f ormal l y i dent i cal i f

    V = L2/ 2mr2 + V.

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    (c) I f t he el ect ron i s bound, V( r) < 0. Cl ear l y L2/ 2nr2 > 0

    ( recal l t hat L i s a constant f or cent ral forces) . For smal l

    enough r, L2/ 2mr2 | v(r)| and V' > 0, i ndi cat i ng a repul si vecore i n the one- di mensi onal f ormal i sm. Oi l y i f V r -*1, n > 2

    wi l l t hi s core di sappear (unl ess L = 0).

    9-18

    (a) The potent i al i n quest i on i s V' i

    V' = V + L2/ 2mr2.

    Now, i n el ect ron vol ts,

    L2 = H I + 1)H2 _ J S L + 1) = (13. 6)ML +_ U.

    2mr 2 2mr2 2ma2 (r/ aQ)2 (r/ a0)2

    Cl ear l y, f or 1 = 0 , v' = V; see Pr obl em9- 13. For 1=1 ,

    v'(r) v

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    (b) E2 = - 220 eV.

    (c) The cl assi cal regi on of mot i on i s shewn on t he sketch: i t

    f al l s wi t hi n the range f or whi ch P2i *r ' Fi 9- 9- 10, i s l arge

    (1 = 1).

    (d) For !. = 0 see Fi g. 9- 13. The cl assi cal l y permi t ted regi on

    there f al l s wi thi n r = 0 . 2aQ, a bi t smal l er than f or i - 1 .Thi s resul t al so cor responds roughl y to Fi g. 9-10, where P->q i s

    l arge at r = 0. 5a . There i s gual i t at i ve agreement between

    cl assi cal and quant umresul ts.

    9-22

    (a) Fran Fi g. 9-15, the i oni zat i on energy f or the f i rst el ectron

    i s 24 eV. I n t he ground st ate the energy of t he atern, f ranFi g. 9-6, i s -78 eV. Thus t he energy af t er the f i r st el ectron i sraroved i s - 78 + 24 = - 54 eV. The energy wi t h both el ect ronsranoved i s zero; t hus t he energy needed to remove the remai ni ngel ect ron i s 54 eV.

    (b) Wi t h the f i r st el ect ron gone, t he hel i umat an resembl es ahydrogen atan wi t h Z = 2. For such an at cmthe ground stateenergy wi l l he

    and theref ore 54. 4 eV are requi red to i oni ze i t . Agreement wi th(a) i s excel l ent .

    E1 = Z2(E1h) = 22( -13. 6) = - 54. 4 eV,

    9-23B = 0mmitmt

    L

    " kiM\

    6

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    (c) I n the x- ray di agramt he l evel s are i nverted, t he groundst ate i s t aken as zero energy, and the energy i s pl ot t ed cn al ogar i thmi c scal e.

    ' *86

    eo

    *#

    nn t i f -1 T 1 T 1 T I T l H f

    (d) When the hol e i s i n an i nner shel l t he energy di f f erencesf or l i kel y t ransi t i ons are l arge; t hus the x- ray di agram,pl ot t i ng l ogE, i s easi er to handl e than the st andard di agram.

    (e) When the hal e i s i n an out er shel l , t he t ransi t i ons aremor e l i kel y to be opt i cal , and the associ at ed energy di f f erencesare smal l . Hence, the st andard di agrami s adequate.

    9- 24

    The phot on energi es are

    EheX

    E(keV)1. 2400X (rm)

    Use of t he l ast expressi on gi ves t he fol l owi ng:

    K ( M) : Xa

    Kg (M*K): X

    Ky (N*K): X

    0. 0210 rm, E = 59. 0 keV;

    0. 0184 rm, E = 67. 4 keV;

    0. 0179 nm, . E - 69. 3 keV.

    For t he absorpt i on edge, E = 1. 2400/ 0. 0178 = 69. 7 keV = energy

    needed t o i oni ze the atcmby r emovi ng an el ect ron f ran t he K

    shel l . Hence, ^ = 0 ( gnxmd state) + 69. 7 = 69. 7 keV = energyof the at cmwi t h a hol e i n the K shel l . Then E^ - 69. 7 - 59. 0

    = 10. 7 keV; si mi l ar l y, = 69. 7 - 67. 4 = 2. 3 keV and =

    69. 7 - 69. 3 = 0. 4 keV.

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    () LMN

    9- 25

    (a) Hi e I*, l i ne i s emi t t ed when a hol e j unps f ran the n = 2 toan n = 3 l evel . The energy requi red f or thi s i s approxi mat el ythe energy needed t o i oni ze the atan by rerrcvi ng an n = 2el ect ron. Usi ng the one- el ect ron f ormul a wi t h = Z - 10,

    E2 = - ( ) 2(13. 6) = - I 2'6 )2(13. 6) = - 870 eV.

    Thus t he requi red vol t age i s about 870 V.

    (b) The wavel engt h i s obt ai ned f ran

    _ F - fA VE3 - E2 " -E2 870 eV; A = 1. 4 nm.

    9- 26

    (a) TTi e empi r i cal f ormul a i s

    A- 1 = C( Z - a)2; A- ^ = C%(Z - a) ._!

    Thus a pl ot of A vs. Z i s a st rai ght l i ne wi t h a Z- i nterceptof Z = a and a sl ope of / C. Fran Fi g. 9- 18, t he Z- i ntercept = a= 1. 7. Al so

    sl ope =0 s = J t - :~17~ (105)! C = 8, 65 x l t)6 m_1-

    (b) For a: a = 1. 7; C = = 11 x 106 nf 1.

    9- 27

    (a) The K absorpt i on edge (n = 1) shoul d be gi ven by

    Eedge =

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    H t u s ,

    Cohal t : E* = (13. 6) P - f 2 -)2= 8. 5 keV,

    i ron: ^ = (13. 6) & - f - h 2 = 7. 83 keV.

    (b) For phot on energi es great er t han 7;83J W* J ^t hat i ron wi l l absorb the photon di mi ni shes shar pl y. Wi t h 8. 5greater t han 7. 83, and si nce 8. 5 keV f al l s near t he K edge f orcobal t , where t he probabi l i t y f or absorpt i on i s hi gh, a Photon

    energy near 8. 5 keV woul d be best .

    9- 28

    For the i nner el ectrons, t he wave f unct i ons are essent i al l yhydroqeni c, wi t h an appropr i ate ef f ect i ve Z. For t he Kq l i ne,

    use

    *100 = (z/ a0)3/ 2e_Zr / a,

    *210 = 47^0 ^ V 572- 2172300086'

    wi t h the sel ect i on rul e t&= i l - Hi e mat r i x el ement i s

    Pf l = l / ^ d r l - - & 2 ^ r V 3Zr ^ ^s i n e d 6 d * d r | .

    Si ncer = rsi n6cos$I + rsi n6si n*3 + rcosSk,

    t he Z- dependence fol l cws f rctn

    J o

    le- 3Zr / 2a0dr = z

    (3Z/ 2aQ)

    The l i f et i me becones

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    i 3Eoh 3 ^Pb

    T = B = 16h 3v 3Pj 1 ^ TH

    By Exarrpl e 9-8,

    hv - F* = Z*f f .

    Theref ore,

    TPb ZH. ef f ZPb. ef fT|1 ZPb, ef f ZH, ef f

    (___i___) 4 = 2 .44T 82 - 2

    H

    3 2Vf i . H

    3

    Wf i . P b

    < ^ > 4,Pb, ef f

    x 10- 8,

    Th = 10~8 s * Tj = 2. 44 x 10"16 s.

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    CHAPI TK TFH

    J f cl

    E = Ej p - E2g = - 3. 50 - (-5. 35) = 1. 85 eV.

    For photons.

    so t hat

    . . , 1240X(nm) - Ef i vT'

    X = = 670. 3 nm= 6703 A.

    (b) By Exampl e 10-1,

    ,, hcdE he dE , dEd x =- 2_ = T T x T -

    Fr an Tabl e 10-1, dE = 0. 42 x 10~4 eV, and theref ore-4

    dX = (670. 3)- 421_Xp510 = 0. 0152 r m= 0. 152 L

    10- 3

    y 7 fi i(a) The ground st at e conf i aurat i on i s I s 2s 2p 3s , t he f i rstthree shel l s bei ng cl osed; t he possi bl e exci t ed stat es wi l l be

    t hose wi t h the opt i cal el ectron i n t he 3p, 3d, 4s, 4p, 4d, 4f , 5s etc.l evel s, ai t 4d, 4f l i e above 5s and 4s l i es bel cw 3d. Al so, f orany n, the l evel wi t h maxi mumpermi t t ed 1 ( =n - 1) correspondst o the hydrogen at an l evel of t hat n. That i s, f or 3d (n = 3,1 = 2),

    E = E3H = - 1. 5 ev.

    (b) Each l evel , except s-states, i s spl i t i nto t wo l evel s, wi t ht he stat Q of smal l er j bei ng more neoat i ve i n enerqy. The encr oy

    spl i t t i ng i s snai l compared t o t he ener gy of t he degeneratestates. Thi s spi n- orbi t spl i t t i ng i s gi ven by

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    AE = 7 5 : (j + D - + X) - s( s + 1)}, c

    AE =K{j (j + X) - Ml + X) - s(s + X)}.

    Assume K = K(r=0) = constant . I n al l states s = , 2s + X = 2,j = I *s, except 1 = 0 wher e j = s. Put t i ng al l t hi s tooethergi ves t he resul t s bel ow.

    3s: 1 = 0 , j = X/2; AE = 0; S/ 2-

    3p: . = X,r 3 = 3/2; AE = +K; S / 2 .

    Ol j = X/2; AE = - 2K;

    X/ 2

    4s: = 0; j = X/2; AE = 0; S / 2

    3d: I = 2 ;r j = 5/2; AE - 2K; S / 2 -

    l j = 3/ 2; AE = - 3K; S/ 2 .

    4p: I = I ;j j = 3/2; AE = K; S/ 2 '

    O*j = 1 / 2 ; AE = -2K; S / 2

    5s: I = 0; j = 1 / 2; AE = 0; CNsH

    sel ect i on rul es are: At = i x, Aj = 0 , 1 . Uiai ves f or the permi t t ed t ransi t i ons:

    2Sj y2 2P1/2 ' S / 2 " 69011of ^ 3s, 4s, 5s l evel s can make atransi t i on t o each of t he t wD l evel s oft he 3p, 4p states.

    * 2D, , - . But not t o si nce t hen Aj = 2.111 Al so t o the S- st ate above.

    2P, /, 2D, . _, 2D, . These i n addi t i on to the S,3/ 2 / t ransi t i on. L/*

    S/ 2 ' S / 2 These are i ncl uded above.

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    Pitbnut S5pio-*>rbit Splitting

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    (a) Ij, = 1, P.2 = 2; s1 = s2 = %. Thus t he possi bl e val ues of J.'

    ar e It = 3, 2, 1; possi bl e s' = 1, 0. The snal l est 4 , s' i s thest ate of maxi i rameneray: i . e. , 4' = 1, s' = 0 . Wi t h 4' = 1 , s' =

    0, there i s onl y one possi bl e j ' : t o wi t , j * = 1 .

    (b) Si nce 5' = 0 , ' l i es al cnq 3'.

    10-5

    = 2, H2 = 3; = s2 = lj. The possi bl e 4' = 5, 4, 3, 2, 1; t he

    possi bl e s' = 1, 0. For j 1:

    j ' = V + s , V + s - 1 , . . . |SL' - s' |

    Theref ore, t he possi bl e conf i gurat i ons are:

    i l si 1 1

    5 1 6, 5, 45 0 54 1 5, 4, 34 0 43 1 4, 3, 23 0 32 1 3, 2, 12 0 2

    1 1 2, 1,01 0 1

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    For the conf i gurat i on 4s3d, ^ = 0, l2 = 2, = s2 = >s. Hence,

    V = 2 onl y, s' = 1, 0. Wi t h V = 2, s' = 1, j ' = 3, 2, 1 gi vi ng

    3D, - . l evel s. For i ' = 2, s' = 0, j ' = 2 onl y, resul t i ng i n a

    VJ , 12 state. By t he Lande i nterval rul e, the separat i on i s(3D3 - 3D2) / (3D2 - 3Dj ) = 3/ 2.

    The energy shi f t s themsel ves are

    AE = K{j 1(j 1 + 1) - t ' d' + 1) - s 1( s1 + 1)},

    gi vi ng

    *D2: AE = 0;

    3D3: AE = 4K;

    3D2: AE = - 2K;

    AE = -6K.

    The l at ter t hree shi f t s obey the Lande rul e.

    = i . r = 2

    - - r = 2 . 3 2

    Splitting cb1e 1 - 1 ^

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    The magni t udes of the vectorsare:

    J' = / 12H; L' = / 6K; S' = / 2K.Appl yi ng the cosi ne l aw:

    S' 2 = J ' 2 + L' 2 - 2J ' L' cos0,

    2 = 12 + 6 -2/ 72COS0,

    0 = 19. 47*.

    Agai n resort i ng t o the cosi nerul e:

    j ' 2 = s' 2 + L' 2 + 2S' L' cos,

    12 = 2 + 6 + 2/ l 2cos*,

    = 54. 74.

    Turni ng t o the magnet i c moments:

    ws - T 5' = 2/2V

    ' i = F l ' = / 6V

    V = v's2 + uj 2 + 2p cos * ,

    U2 = 8y + 6p + 4/ l 2ucos54. 74 u = 4. 6903 .

    Fi nal l y,

    Mg2 = U 2 + U2 2Pj J ucosa,

    P = 6 21. 999 - 2/ 6(4. 6903)cosa * a - 29. 50,

    so that Mu, - 3 > = 29. 50" - 19. 47 = 10. 03*.

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    10-9

    (a) On Fi g. 9- 13, t he col umns reveal t he l ast shel l bei nq f i l l ed,the row the numbers of el ect rons i n that shel l . Theref ore,

    12Mq: I s2, 2s2, 2p6, 3s2;

    13A1: I s 2, 2s 2, 2p6, 3s2, 3pX,

    14Si : I s2, 2s2, 2p6, 3s2, 3p2.

    (b) 12Mg; t he conf i gurat i on represents a f i l l ed shel l , and thusal l t he angul ar mcment a are zero, l eadi ng t o i Sg.

    Al t there i s a si ngl e val ence el ect ron (s = s' = %); thus2s' + 1 = 2; ' = 1 gi vi ng a P- state; j ' = 3/ 2, 1/ 2 wi t h thesmal l er j * l yi ng l ower, l eadi ng to 2p .

    14Si : here there are tw> 1 =1 el ectrons; s' = 1, 0 and 8.' = 2, 1,0. For t he l ower energy pi ck the l arger s' . Thi s gi ves aspossi bi l i ti es:

    V = 2; j ' = 3, 2, 1;

    * =1; j * . 2, 1. 0, \ 1>0

    V = 0; j ' = 1; 3Sr

    The 3d , and 3S1 st ates are, however , prohi bi t ed by theExcl usi on pr i nci pl e. Of the 3p2 x q states, t he snal l est j ' l i esl owest ; hence t he ground st at e conf i gurat i on shoul d be 3pQ.

    1 0 - 1 1

    For a si ngl e nul t i pl et s' and I ' have t he same val ue f or eachl evel . By t he i nterval rul e.

    *4 = *4

    r .s

    *3 = 2Kj 4,

    S2 = 2Kj 3, - - - - - 3

    E! = *12- 7

    " ' l

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    V * 3 = 3 = j 5/ j 4 = (j 4 + 1) / j 4; j 4 = 3-

    Si nce j = 1, j 5 = 4, j 4 = 3, j 3 = 2, j 2 = 1, j x = 0. But

    j ' = i ' +s' , t ' +s' - l , . . . U - s' l ,

    so that

    + s' = 4, I' - s' = 0; S.' = s' = 2,

    and hence the resul t s are

    r = s' = 2; j ' = 4, 3, 2, 1, 0.

    10- 14

    (a) The g- f actor i s

    j d' +l ) + s Ms +l ) - t ' ( t ' +l )9 - 1 2j " (j ' +l )

    (i ) For q > 2,

    j ' ( j ' +l ) < s' (s' +l ) - I ' t t ' +l ) . (*)

    I f j ' =8. ' + s' , t hi s becomes

    0 < -(V2 + V + H' s' ) ,

    whi ch i s i mpossi bl e. But i f j ' =V

    - s' t he rel at i on gi vess > I,

    so that j ' = s' - V, a cont radi ct i on. So t r y j ' = s' - I ' i n(*), whi ch wi l l now reduce to

    I' 2, as requi red.(i i ) For the case g < 1, t he f ormul a f or g requi res t hat

    j ' ( j ' +l ) + s' (s' +l ) < t ' t t ' +l ) . (**>

    I f j ' = V + s' , (**) becomes

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    0 > s 2 + s' + 4' s' ,

    whi ch i s i mpossi bl e. But i f j ' = 4' - s' , (**) reduces t o

    4' > s' .

    For exampl e, 4' = 2, s' = 1, j ' = 2 - 1 = 1, g = %< 1.

    (b) Consi der t hi s second case: 4' = 2, s' = 1, j ' = 1, q = %Then,

    L' = / 6X, S' = /2tf, J ' = / 2H, *( t ' , 2' ) = 150*.

    Si nce g = 1, os = 2, dr aw egual i n l ength to ' , twi ceas l ong as S' ; i t i s seen that i s about hal f as l ong as J ' ,i ndi cat i ng t hat g = %.

    10- 17

    (a) The yi el ds three l evel s, t he 3P2 f i ve, ^ three, andt he j Pq gi ves one; thus t he total ni tnber i s 12.

    (b) For t he 3s el ect ron 1=0; 2(24+1) = 2;For t he 3p el ect ron 4 =1; 2(24+1) = 6.

    Cl ear l y, wi t h (6)(2) = 12, the f i el d has removed t he deoeneracycompl etel y.

    10-Ift

    For a si ngl et s = 0, so there i s onl y orbi t al angul ar mcment umt o consi der . The pot ent i al energy of or i ent at i on i s

    AE = - J -fc.

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    f or or bi t al ancj ui ar moment um g = 1 so that

    U_ . e

    L 2m' 11 " HI f $ i s i n t he z- di rect i on,

    AE = - . 5 = - LzB = -

    gi vi ng r i se t o 2S.+1 l evel s. Si nce s = 0, I = j ; maki ng thi ssubsti tut i on, and i nser t i ng a f actor g = 1 , l eads to

    AE = - i gai y

    whi ch agrees wi t h Eq. 10- 22 i n t he case g = 1.

    10-19

    I n the cl assi cal model , pi cture t he magnet i c f i el d bui l di ng upto a val ue B f romzero i n ti ne T. Faraday' s l aw requi res ani nduced el ectr i c f i el d E,

    r, i _ BK = dt = *r T'

    Thi s i mparts an addi t i onal vel oci t y Av t o the el ectrons, whi chci rcul ate ei t her cl ockwi se or countercl ockwi se. Hence,

    Av = aT = T = T = | ( | S) T =m m m 2 T 2m

    The new speeds are

    yi el di ng f requenci es v gi ven by

    v j . gBv 2nr v0 " 4nm'

    E = hu = hv0 1 B'

    AE = \ilB,

    correspondi ng t o Eq. 10- 22 wi t h g = 1, Arnj = 1.

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    10-20

    (a) For 1P1, j ' = 1 so there ar e t hree l evel s; t he h>2 has j ' =

    2 gi vi ng r i se to f i ve l evel s wi t h t he f i el d. For bot h these

    st at es s' = 0 so that g = 1 and AE = j . Hence, t he l evel

    spaci ngs are the same f or each state.

    (b) The sel ect i on rul es are Amj = 0, l l , al l owi ng zero to zero

    si nce Aj ' ^ 0 between t hese states. Tti e group I of t ransi t i ons

    gi ve t he same wavel engt h as when B = 0; f or I I , AE < A E ^ so

    that Xj j > XQ; i n I I I , AE > A E ^ and theref ore Xm < XQ. Al so,

    wi t h al l the l evel spaci ngs the same, al l wavel engt hs i n I I are

    equal , as are al l i n I I I . Group I has wavel engt hs equal t o t hose

    wi t h B = 0 and so are al l equal . Hence, three l i nes appear.

    (c) The wavel engt h of a l i ne i s gi ven by

    X = *.A AE'

    Consi der i ng two t ransi t i ons whose energi es di f f er by A E, thewavel engt hs of these l i nes di f f er by

    AX = I W a (AE) = - ^A ^.(AE)2

    New cl ear l y.

    XI I X0 ~ X0 XI I I '

    and consequent l y AXI X = = AX XXI - XQ. The energy AE,

    cor respondi ng t o 0, gi ves wavel engt h XQ, whi ch i s

    i dent i cal t o that f or ^ when B = 0. Fran Fi g. 10-8, thi s

    i s

    AE ~ 10 - 3. 6 = 6. 4 ev = 10. 24 x 10- 19 J .

    Si nce Am! = 1, A*E = Bf Arn ) =1^6= (9. 27 x XO- 24) (0.1) =

    9. 27 x 10- 25 J . Theref ore

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    n - n b* a

    \

    /

    33: : 3

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    J! = D

    (*)iir-orht *plittinBignnrtA)

    /

    /

    s j

    n

    -- +5 +1

    ---------------- ------

    . +% 0

    +1, - 1 tmd- f ni a"-ij +1 dr gcmmcB

    --l i -1

    - +% 0

    So litti hue tljs raif manf-

    lcngtl) * B = II lint. .

    X3 X33 *333

    (!) s' =%, * ; = f t . *' = ) i -i = Usi ng the

    rel at i on f or fiE, these gi ve:

    1j L

    AE (uni ts

    1 +% +2

    1 ->} 0

    0 +% +1

    0 -*s - 1

    - 1 +>J 0

    - 1 ->s -