vật lí dc 3

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Vt l c 3 thy Trn Thin c

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  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    HNG DN GII BI TP NH HNG TUN 1 - 2

    CC DNG TON KHE YOUNG C BN

    DNG 1: NGUN S DCH CHUYN

    Hnh 1.1. H khe Young ngun S dch chuyn

    - Hiu quang l (hiu ng i) t ngun S:

    o Ti vn sng:

    o Ti vn ti:

    Xt vn sng trung tm: {

    - Nhn xt:

    o H vn dch chuyn ngc hng vi chiu dch chuyn ca ngun S

    o Mi quan h gia dch chuyn l:

    DNG 2: H KHE YOUNG BN MT SONG SONG

    Hnh 1.2. H khe Young bn mt song song

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    - Khong vn:

    - V tr vn sng bc k:

    - V tr vn ti: (

    ) (

    )

    - Hiu quang l (hiu ng i):

    o Ti vn sng:

    o Ti vn ti:

    - Bn mng chiu dy e, chit sut n:

    o Vai tr ca bn mng:

    lm chm qu trnh truyn nh sng (chit sut lm vn tc

    truyn nh sng b gim i)

    ko di ng i ca tia sng mt on: (n 1)e hiu quang

    l thay i

    Xt vn sng trung tm:

    h

    vn s dch chuyn v pha khe c t bn mng

    o Lin h gia n, c, v trong bn mng:

    BI 1.2: Khong cch gia hai khe trong my giao thoa Young a = 1mm. Khong cch t mn quan st ti mt phng cha hai khe D = 3m. Khi ton b h thng t trong khng kh, ngi ta o c khong cch gia hai vn sng lin tip l i = 1.5mm.

    a. Xc nh bc sng ca nh sng ti b. Xc nh v tr ca vn sng th 3 v vn ti th 4 c. t trc mt trong hai khe sng mt bn mng phng c hai mt song song,

    chit sut n = 1.5, b dy e = 10m. Xc nh dch chuyn ca h thng vn giao thoa trn mn quan st.

    d. Trong cu hi c nu y nc (chit sut n = 1.33) vo khong cch gia hai bn quan st v mt phng cha cc khe th h thng vn giao thoa c g thay i? Hy tnh khong cch gia hai vn sng lin tip trong trng hp ny.

    Tm tt: a = 1mm

    D = 3m

    i = 1.5mm

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    n = 1.5

    e = 10m

    Xc nh: ; ; x0; i' Nhn xt: Cu a v b lin quan ti bi ton khe Young c bn. Ta ch cn s dng

    cc cng thc tnh bc sng v xc nh v tr vn sng, vn ti trong h khe

    Young. Cu c l bi ton khe Young bn mt song song. i vi bi ton bn mt

    song song ta cn ch l khi c bn mt t trc khe no th h vn s dch

    chuyn v pha khe vi dch chuyn x0. Trong cu d, phn tch ta thy khi h

    thng c y nc th bc sng s b thay i do khong vn cng s

    thay i theo.

    - Bc sng ca nh sng ti:

    - V tr vn sng bc 3 (ng vi k = 3):

    - V tr vn ti th 4 (ng vi k = 3):

    (

    )

    - dch chuyn ca h vn khi c bn mt:

    - Bn mng ch ng vai tr lm dch chuyn h vn ch khng lm thay i

    khong vn. Khi nc vo h khe Young th bc sng

    khong

    vn s gim i n ln

    h vn st li mt khong l

    0.375mm

    BI 1.3. o b dy ca mt bn mng trong sut, ngi ta t bn trc mt trong hai khe ca my giao thoa Young. nh sng chiu so h thng c bc sng

    = 0.6m. Chit sut ca bn mng n = 1.5. Ngi ta quan st thy vn sng chnh gia b dch chuyn v v tr ca vn sng th nm (ng vi lc cha t bn). Xc nh b dy ca bn. Tm tt:

    = 0.6m n = 1.5

    x0 = xS5

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    Xc nh e Nhn xt: y l bi ton khe Young - bn mt. T cng thc tnh dch chuyn

    ca bn mt ta thy nu bit trc chit sut n, D, a, x0 ta c th xc nh c b

    dy ca bn mt.

    - T d kin bi ta c:

    Bi ton tng qut: vn sng chnh gia b dch chuyn v v tr vn sng th k hoc

    vn ti th k p dng cng thc cho tng trng hp ta d dng thu c cng

    thc tng qut.

    BI 1.4. o chit sut ca kh clo ngi ta lm th nghim sau: Trn ng i ca chm tia sng do mt trong hai khe ca my giao thoa Young pht ra, ngi ta t mt ng thy tinh di e = 2cm c y phng v song song vi nhau. Lc u trong ng cha khng kh, sau thay khng kh bng kh clo, ngi ta quan st thy h thng vn dch chuyn i mt on bng 20 ln khong cch gia hai vn sng lin tip (tc 20 ln khong vn). Ton b th nghim c thc hin trong bung yn tnh v c gi mt nhit khng i. My giao

    thoa c chiu bng nh sng vng natri c bc sng = 0.589m. Chit sut ca khng kh n = 1.000276. Tm chit sut n ca kh clo. Tm tt: e = 2cm

    = 0.589m n = 1.000276

    x0 = 20i

    Xc nh n

    Nhn xt: y l bi ton Young bn mt, trong h Young bn mt c ng

    dng xc nh chit sut ca kh Clo. Quan st cng thc xc nh dch

    chuyn ta thy xc dnh c chit sut n ca Clo ta cn bit D, a, e, x0

    - T d kin bi ta c:

    ( )

    (

    )

    n' = 1.000865

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    Ch : i vi bi ton ny ta cn bit chit sut trong cng thc tnh dch

    chuyn ca h vn l chit sut t i ca cht lm bn mng so vi chn khng (

    trong bi ta coi nh l so vi khng kh v chit sut khng kh v chn khng l

    gn nh nhau).

    BI 1.5. Hai khe sng trong my giao thoa Young cch nhau a = 1mm c chiu sng bi mt chm tia sng n sc. Mn quan st giao thoa c t cch mt phng ca hai khe mt khong D = 2m. B rng ca 6 vn sng lin tip o c l 7.2mm.

    a. Tnh bc sng ca nh sng ti b. Tnh sai s c th mc phi khi o bc sng, bit rng sau sai s ca php

    o, khong cch gia hai khe v b rng ca 6 vn sng u bng 1/20mm c. Xc nh dch chuyn ca h thng vn, nu trc mt trong hai khe sng

    c t mt bn mt mng trong sut, mt song song, dy 0.02mm chit sut n = 1.5.

    Tm tt: a = 1mm

    D = 2m

    6 vn sng rng 7.2mm 5i = 7.2mm L = 1/20mm e = 0.02mm

    n = 1.5

    Xc nh , , x0

    Nhn xt: Cu a l mt cu kh n gin v ch vic ng dng cng thc c bn

    tnh ra bc sng, ch y chnh l i lng khong vn i c cho gin tip

    qua d kin b rng ca 6 vn sng lin tip o c l 7.2mm. Xt mt cch

    tng qut, N vn sng lin tip tng ng vi N 1 khong vn. Cu b l mt

    cu lin quan ti kin thc v sai s. T cng thc tnh bc sng ta c th xy

    dng c cng thc tnh sai s tng i ca bc sng

    Cu c l bi ton Young bn mt d dng x l cu ny (qu d)

    - Khong vn:

    - Bc sng ca nh sng ti:

    - Sai s tng i ca bc sng l:

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    (5i = 7.2 mm nn sai s i = (1/20)/5, sai s ca php o D c th ly l

    1mm v bnh thng chng ai o kch thc c m m li dng thc o c

    sai s l 1/20 mm)

    - Sai s tuyt i ca bc sng l:

    - dch chuyn ca h vn khi c bn mt:

    BI 1.14. Chiu mt chm nh sng trng xin mt gc 450 ln mt mng nc x phng. Tm b dy nh nht ca mn nhng tia phn chiu c mu vng. Cho

    bit bc sng ca nh sng vng l 0.6m. Chit sut ca bn l n = 1.33. Tm tt:

    = 450 = 0.6m n = 1.33

    Xc nh dmin

    Nhn xt: y l bi ton giao thoa bn mng cc bc chnh gii bi ton

    ny l:

    B1: Xt hiu quang l gia hai tia phn x trn b mt ca bn mng:

    B2: Xt iu kin vn sng vn ti:

    - Vn sng:

    - Vn ti: (

    )

    T d kin ca bi ta thy tia phn chiu l mu vng th hiu quang l phi

    bng k (trong l bc sng ca nh sng mu vng).

    Bi ton yu cu ta xc nh b dy nh nht. T cng thc trn ta thy b dy nh

    nht khi k = 0 ta c:

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    BI 1.19. Chiu mt chm tia sng song song = 0.6m ln mt mng x phng (chit sut bng 1.3) di gc ti 300. Hi b dy nh nht ca mng phi bng bao nhiu chm tia phn x c:

    - Cng sng cc tiu - Cng sng cc i

    Tm tt:

    = 0.6m n = 1.3

    = 300 Cng sng cc i:

    Cng sng cc tiu: (

    )

    Xc nh dmin

    Nhn xt: y l bi ton giao thoa bn mng s dng cng thc xc nh hiu

    quang l.

    - Xt hiu quang l gia hai tia phn x trn hai mt ca bn mng:

    - TH1: Cng sng cc i: , dmin k = 0

    - TH2: Cng sng cc tiu: (

    ) , dmin k = 0

    (

    )

    BI 1.21. Mt chm tia sng n sc bc sng = 0.6m c ri vung gc vi mt mt nm thy tinh (chit sut n = 1.5). Xc nh gc nghing ca nm. Bit rng s vn giao thoa cha trong khong l = 1cm l N = 10. Tm tt:

    = 0.6m n = 1.5

    l = 1cm

    N = 10

    Xc nh

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    Nhn xt: y l bi ton giao thoa trong nm c chit sut n. Ty theo b dy ca

    nm m cc vn ti c th l vn sng hoc vn ti.

    - V tr ca vn ti:

    (k = 0, 1, 2,.)

    - V tr ca vn sng:

    (k = 1, 2, 3, )

    Ta xt v tr vn ti th k v vn ti th k + 9 gy bi nm c chit sut n (v khi

    nh sng truyn qua mi trng c chit sut n bc sng s gim i n ln)

    -

    -

    T hnh v ta thy:

    v rt nh nn

    BI 1.22. Mt mng nc x phng chit sut n = 1.33, c t thng ng, v nc x phng dn xung di nn mng c dng hnh nm. Quan st nhng vn

    giao thoa ca nh sng phn chiu mu xanh (bc sng = 0.5461m), ngi ta thy, khong cch gia 6 vn bng 2cm. Xc nh:

    a. Gc nghing ca nm b. V tr ca ba vn ti u tin (coi vn ti s 1 l vn nm giao tuyn gia

    ca hai mt nm). Bit rng hng quan st vung gc vi mt nm. Tm tt: n = 1.33

    = 0.5461m N = 6 vn

    l = 2cm

    Xc nh , xt1, xt2, xt3

    Nhn xt: Bi ton ny tng t nh bi ton 1.21 ch khc ch bi ny l nm

    x phng c chit sut n = 1.33. Khi xt quang l ca mt tia sng ta cn ch nu

    tia sng phn x trn b mt c chit sut ln hn chit sut mi trng ang

    truyn th quang l ca tia sng s di thm

    . Nu tia sng truyn trong mi trng

    c chit sut n v c chiu di d th quang l ca tia sng s l nd (iu ny c th

    d hnh dung bng v d sau: nu chng ta i t A n B m khng c vt cn

    (chit sut n = 0) th qung ng chng ta i c l AB nhng nu trn ng i

  • GV: Trn Thin c - http://ductt111.wordpress.com V2012

    c vt cn (chit sut n khc 0) th chng ta phi i lng vng th mi n c B

    v do qung ng thc t chng ta i c s di hn qung ng AB)

    - Hiu quang l ca cc tia phn x trn mt nm s l:

    - Gi s ti M l vn ti ta c:

    - Xc nh v tr vn ti th k:

    o Do rt nh nn ta c gn ng:

    o T y ta c v tr vn ti th k l:

    - Khong vn giao thoa s l:

    - Gc nghing ca nm l:

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