Tài liệu Luyện thi cấp tốc các dạng bài tập từ các đề thi quốc gia môn vật lý (nxb đại học sư phạm 2011) - phạm đức cường

pHAM DLfC CLfdNG (Chu bien) E TAN Rl - BUI IRAN DLfC ANH THAI, THAN THANH SANG 530.076 L527TH CAC DANG BAI TAP TQ CAC D E THI QUOC GIA (TOT NGHIE P - T U Y E N kINH) VAT^Y / ^ C a c de c h i n h thiic v a de l u y ^ n t a p p a n va thang diem ciia B Q Giao due va Dao tao (Tai b a n , svfa chvTa v a bo sung) Cho mach dien xoay chieu nhif h i n h ve. Bi^t cuon day c6 dien t r d khong ~ dang ke. K h i khoa k dong dong dien qua mach cham pha hofn dien ap hai _ d^u mach la —. K h i khoa k md dong dien qua mach nhanh pha .i....:4„:..,,_4_.i. horn dien ap hai dau mach la —. 4 Moi lien he giOfa cam dung khang Zc cua ma -|i4 A. Z L = (V3 + DZc D V L 0 1 C. Z:. = ^ D. ZL = M 1 1 7 0 (73- DZC NHA XUAT BAN DAI HOC Si/ PHAM PHAM DLfC CLfdNG (Chu bien) LE TAN Ri - BUr TRAN DISC ANH THAI - THAN THANH SANG LUYEN THI CAP TOC • CAC DANG BAI TAP TlT CAC OE THI QUOC GIA (^at nqklift - ^tufln dnh) VAT L Y Cac de chinh thCfc va de luyen tap Dap an va thang diem cua Bg Giao due va Dao tqo (Tdi ban, sura chufa va bd sung) THt; V i a ; TNVH BiNH VHUAW NHA XUAT BAN DAI HQC Si/ PHAM MUC L U C Phan 1: Tom tat giao khoa 49 53 53 54 56 B. Phan rieng cho chirong trinh nang cao Dpng lyre HQC vat ran Con lac v§t K Hi?u img Dop-ple Thuyet tuong doi h^p Thuyet Big bang 3 6 13 17 25 31 37 43 A. Phan chung cho cce ban va nang cao Dao dpng ca Song ca Dao dpng di^n tir - song difn tir Dong di?n xoay chieu Song anh sang Lugng tir anh sang H^t nhan nguyen tir Tir vi mo den vT mo Phan 2: Kien thirc can nhor 77 80 80 80 82 B. Phan rieng cho chirong trinh nang cao Ca hpc v^t ran Con lac v§t li Hi?u irng Dop-ple Quang di$n Tia X (Ronghen) 58 64 66 69 70 73 74 A. Phan chung cho co ban va nang cao Dao dpng CO Song ca Dong di?n xoay chieu Dao dpng di^n tu Song anh sang Quang di^n Vat li h^t nhan Phan 3: Dap an va huoTig dan giai cac de on luyfn Tu Tai Phan 4: Dap an va hv&ng dan giai cac de on luyf n Dai h9c - Cao dang 83 190 ^han t: Phan TdM T A T G I A O K H O A chujif cho ban of ban ad ndn^ eao DAO DONG CQ I. Dao d9ng dien hoa : * Dao dpng tuan hoan la dao dpng ma trang thai chuyen dpng cua vat dupe l$p lai nhu cij sau nhung khoang thai gian bSng nhau. * Chu ky la khoang thai gian ngan nhat de tr^ng thai dao dpng cua v^t l^p l^i nhu cu hay thai gian thvrc hi?n 1 dao dpng toan phan. * Dao dpng dieu hoa la dao dpng dupe mo ta bang djnh lu^t dang cos hoae sin: X = Acos(cot+ (p) Vai: + X la li dp ciia dao dpng (khoang each dgi sS tir vat den v/ tri can bdng) + A la bien dp cua dao dpng, don vj : m; em (A = + /x„a.x/) CO la tan so goc ciia dao dpng, don vj : rad/s (co cho biit dao dpng nhanh hay chants co Id toe dp bien doi ciia goc phaj + (cot + cp) la pha dao dpng t^i thai diem t, pha chinh la doi s6 cua ham cosin va la mpt goc. (Pha dao d0ng cho ta biet v/ tri vat dao d^ng, gid tri vd each bien thien cua vgn toe va gia toe vat dao dgng. Pha dao dgng xde dfnh trgng thai vat dao dqng). + (p la pha ban dau ciia dao dpng (Pha ban ddu xde dinh trgng thai ban ddu ciia vgt dao d(>ng, ph^i thuQc each chgn goc tog dp vd goc thai gian). + Vgn toe va gia toe v|it dao dpng dieu hoa bien thien cung tan so vai tan so v^t dao dpng. + V$n toe nhanh pha ^ so vai li dp x + Gia toe ngupc pha so vai li dp x * Lye tac diing lam vat dao dQng dieu hoa: + C6d9ngF = - k x + Lvrc nay luon huang ve VTCB nen dupe gpi la \\fc keo ve (hay lye hoi phye). * Dao dpng eiia con lac 16 xo la mpt dao dpng dieu hoa co chu ky: 3 * Voi goc l^ch nho, dao dgng ciia con lac don la mpt dao dgng dieu hoa c6 chu ky: T= 2 n Vg * H f dao dQDg: + thvrc hi^n dao dpng t\ do dupe gpi la hf dao dpng. + Dao dpng t\ do la dao dpng xay ra duoi tac d\ing ciia npi l\rc (Noi each khdc dao dgng tir do c6 chu ky chi phu thuQC cac dgc tinh ciia h^, khong phu thuQC cdc yeu to ben ngoai). + Chu ky cua dao dpng t\ do con gpi la chu ky rieng. Vidu: + Con lac Id xo la rnqt h^ dao dgng (c6 chu ki chiphy thuQC vao m va k), l\cc dan hoi tac dung vac vgt la ngi l\rc. + Con lac dcm va Trdi ddt (hay con lac vgt It vd Trdi ddt) Id h? dao n. Cor nSng: Do v^t n^ng trong con iSc 16 xo chju tac dyng ciia l\rc dan hoi va trong con iSc don la trpng lyc nen ca nang ciia v$t dupe bao toan vi l^rc dan hoi va trpng Ivrc la nhung \\fc the. * Co' nang trong dao d$ng dieu hoa: + The nang: E, = ^ kx^ = ^ kA^cos^(cot + cp) + Dpng nang: Ea = ^ mv^ = ^ kA^sin^((ot + 9) + Ca nSng toan phan: E = E, + E^ = — kA^ =—mco^ = const V$y trong suot qua trinh dao dpng dieu hoa c6 s\f chuyen hoa nSng lupng gi&a the nSng va dpng nSng nhung ca nSng khong doi va ti I9 vai binh phuang bien dp dao dpng. III. Dao dgng t^t dan: Dao dpng tat dan la dao dpng c6 bien dp giam dan theo thai gian do tac dyng ctia ma sat nhot. * D^c diem: + Dao dpng tat dan noi chung khong c6 tinh dieu h6a nhung khi xet trong thai gian ngin ta c6 the coi la dao dpng dieu hoa vai chu ki rieng va tan so rieng. + L\rc can moi truang cang Ian (hay moi triwng cdng nhot) dao dpng tat dan cang nhanh. + Dp nhot cua moi truong tang theo thu t\r: khong khi, nuac, dau, dau rat nhot. 4 T I V . Dao d^ng duy tri: Dao dpng dupe cung cap nSng lupng de bu l^i phan nSng lupng mat di do ma sat ma khong lam thay d6i chu ki rieng cua no gpi la dao dpng duy tri. * Dao dpng duy tri eo ngo^i l^rc tac dyng, ngo^i l^rc nay dupe dieu khiSn + de C O t i n so goe bSng tan so goc dao dpng t\ do cua h?. + boi chinh dao dpng ky qua mpt ca cau nao do. * Tan so va bien dp dao dpng duy tri v i n bSng nhu khi h$ dao dpng t\ do. V. Dao d^ng cir&ng birc: la dao dpng dupe duy tri do tac dyng cua mpt ngo^ii l^rc bien doi dieu hoa: F = FoCosQt + Dao dpng cu&ng buc la dao dpng dieu hoa. + Tan so dao dpng eixong buc bSng tan so ngo^i Ivrc. + Bien dp dao dpng cuong buc ti I9 vai bien dp Fo cua ngo^i lyre va phy thupc tan so cuong buc D. cua ngoai l\rc ( AQQ e | Q - CO| ) . VI. S y C9ng hirong: + Hi?n tupng bien dp dao dpng cu&ng buc tang nhanh den mpt gia trj eye d^i khi tan so f cua lyc cir&ng buc bang tan so rieng cua v^t dao d9ng gpi la hi$n tupng cpng huong. + Bien dp dao dpng d^t den gia trj khong doi va eye khi toe dp tieu hao nSng lupng do ma sat bSng toe dp cung cap nSng lupng cho h^. + Bien dp eye d^i ciia dao dpng khi cpng huong phy thupc ma sat moi truong: ma sat giam thi gia trj eye d^i bien dp ting. * Phan bi?t dao dpng cv&ng birc vol dao d9ng duy tri: + Dao dpng cu&ng buc la dao dpng xay ra dudi tac dyng ciia ngo^i lyc tuan hoan C O tan s6 goc Q bat ki. Khi on djnh dao dpng cuong buc c6 tan so biing tan so ngo^i lyc. + Dao dpng duy tri cung xay ra dudi tac dyng ngo^i lyc nhung ngo^i lyc dupe dieu khien (boi ehinh dao dpng ay) de c6 tan so goc bang tan so goc ciia dao dpng ty do ciia h?. VII. Tong h(fp dao d^ng: * Xet hai dao dpng dieu hoa cung phuong, cung ikn so: X ] = Aicos(cot + cpi); X2 = A2cos(cot + 92) Tong hpp hai dao dpng dieu hoa cung phuong, cung t i n so la mpt dao dpng dieu hoa cung phucmg, cung tan so voi hai dao dpng thanh phan. + Bien dp hai dao dpng tong hpp: A = ^Aj + Aj + Pha ban dau hai dao dpng tong hpp la 9, voi: t a i K p ^ Aisincpi + A^sincp; AiCOSCpi + A2C0S(P2 +2AiA2COs(92 + Neu hai dao dOng thanh phan cung pha: 92 - (Pi = 2kn => A = A , + A2 ; (() = (pi = 92 + Neu hai dao dgng thanh phan ngirgrc pha: 92 - (Pi = (2k + 1 )7t A = Noi chung : A | - A2 ; cp = (pi neu Ai > Aj A, - A 2 < A < A , + A 2 SONG c a I. Song ca: + Song CO hpc la nhCrng dao dpng co Ian truyen trong mOt moi truong. + Song CO du(?c t ^ thanh nha lyc lien ket dan hoi giira cac phan tir ciia moi tmong truyen dao dpng di. Cac phan tir cang a xa tam dao dpng cang tre pha hon. + Khi song truyen chi c6 trang thai dao dpng (pha dao dgng) truyen di con ban than cac phan tOr vat chat chi dao dpng t^i cho. * Song ngang: + Co phuong dao dpng vuong goc vai phuong truyen song. + Truyen trong moi truong c6 l^rc dan hoi xuat hi?n khi bj bien dang l?ch (Vd: Song truyen tren mat nuac, spi day dan hoi, tam kim lo^i mong..). + Song tren m§t chat long la do hpp lyc c5ng mat ngoai va trpng lyc c6 tac dyng giong nhu lyc dan hoi. * Song d9c: + Co phuong dao dpng trung vai phuong truyen song. + Truyen trong moi truong c6 lyc dan hoi xuat hi^n khi bj bien dang nen, dan (Vd: Song truyen tren 16 xo khi 16 xo nen va dan...) II. Cac dai lirQiig dac trirng ciia song : * Chu ky, tan so ciia song: la chu ky, tan so dao dpng chung ciia cac phan tii v^t chat CO song truyen qua va bang chu ky, tan so ciia nguon song =:> Chu ki va tan so khong doi khi song truyen. * Toe d9 truyen song: la toe dp truyen pha dao dpng. Trongrnqtmoi tru&ng toe dQ truyen song khong doi) * Buoc song X: Buac song la khoang each giua hai diem gan nhau nhat tren Cling mpt phuang truyen song va dao dpng ciing pha voi nhau. Buoc song cung la quang duong ma song truyen dupe trong mpt chu ky song. X = vT = ^ f 6 * Bien d9 song: Bien dp song t^ii mpt diem la bien dp dao dpng cua phan t i i vat chat tai diem do khi c6 song truyen qua. * Nang liTQTig cua song: Qua trinh truyen song la qua trinh truyen nang lugng. Nang lugng song tai moi diem t i I9 v a i binh phuomg bien dp song tai diem do. M p t phan tir v$t chat dang dumg yen khi c6 song truyen den se dao dpng, nghia la phan tur do da nh$n dupe nang lugng tir song. Vay qua trinh truyen song cung la qua trinh truyen nang lupng. I I I . PhiroTig t r i n h song : Xet song truyen tir nguon O den diem M each O mpt doan O M = x. Gia sOr phuorng trinh dao dpng t ^ i nguon O la : UQ = Acoscot Song truyen tir O den M mat thai gian to = — Phuong trinh dao dpng tai M each O doan d la: Uyj = UMCO = Uo(t - to) Acos(©t-^) hay U M = A c o s c o t - Y ' ' ) (*) ( • ) cho ta xac djnh l i dp ciia phan tur song t ^ i diem M bat k i tren ducmg truyen song, gpi la la phuong trinh song. * Neu song truyen nguQc chieu vai chieu dircmg true Ox thi phmxng trinh song CO dgng: = A c o s ( — t + — x) Tir (*) ta thay song c6 hai tinh chat: + Tinh tuan hoan theo thoi gian: K h i xet mpt diem P tren song c6 toa dp x = d. Ta thay l i dp u cua P bien thien theo ham cos => chuyen dpng cua diem P la mpt dao dpng tuan hoan vai chu k i T = — . (0 + Tinh tuan hoan theo khong gian: K h i xet tat ca cac diem tren song vao thai diem to, (*) " M = Acos( Y to - Y x) Ta thay l i dp u cua cac diem tren song bien thien tuan hoan theo l i dp x => hinh dang song (hinh sin) tai thai diem to : cu sau mpt buac song thi song lai C O hinh dang nhu truac. 7 D^c bift: + NhiJng diem tren phuong truyen song dao dgng cung pha v a i nguon k h i — x = 2k7i=> x = kX v a i Ikl =0,1,2,... + N h u n g diem tren phuang truyen song dao dpng ngugc pha v a i nguon khi — x = ( 2 k + 1)71=^ x = (k + - ) X A. 2 I V . P h a n x a song: Song dang truyen trong mpt moi truong ma g^p v§t can thi bj phan x^. Song phan X 9 c6 ciing tan so va buac song ciia song t a i . Neu v^t can tyr do thi song phan x? luon luon ciing pha v a i song t a i a d i l m phan x^. + Neu v$t can c6 djnh thi song phan x^ luon luon ngugc pha v a i song tai a diem phan x^. + V . Song d i r n g : Song dCmg la song c6 nhCrng diem dung yen (nut song) va nhOng diem dao dgng v a i bien dp c^rc d^i (byng song) trong khong gian. Dac d i l m : V j tri cac nut va cac byng la c6 djnh. + Song diing la svr giao thoa giua song t a i va song phan x^ tren cdng phuang. + V j t r i cac byng luon each dau c6 djnh nhung khoang bSng mpt so le l4n mpt phan t u buac song. - V j t r i cac nut luon each d i u c6 djnh nhirng khoang bSng mpt so nguyen Ian nua buac song. - 3l + Khoang each giua hai nut (ho$c hai byng) ke nhau dfiu bSng —. Dieu kif n c6 song dirng: - K h i hai dau day c6 djnh: De c6 song dung, chieu dai spi day b^ng so nguyen \kn nua buac song ^ = k | (vai k = 1,2, 3 ; => tren day c6 so byng bang so bo bang k, con so nut lak+ - 1. K h i mpt dau day t y do va mpt dau day c6 djnh: De c6 song dung, chieu dai spi day bang so nguyen le Ian mpt phan t u buac song l = m— 4 (vai m = 1, 3, 5....) => tren day c6 so bung bang so nut bangn = ~~~ -^on so bo Ian -1 ifng dyng cua song dirng: Do v$n toe truyen song. 8 VI. Giao thoa song: * Hai nguon dao dpng cung tin s6 va c6 dp i?ch pha khong doi gpi la hai ngu6n ket hgrp. Song ma chiing t^o ra dugc gpi la song ket hgrp. * Giao thoa la s\c t6ng hgp cua hai song ket hgrp trong khong gian, trong do c6 nhixng cho c6 djnh ma bien dp song dugc tang cucmg ho^c bj giam bat. * Dieu kif n c6 giao thoa: Hai song la hai song ket hgrp va dao dpng cung phuong. * Ly thuyet ve giao thoa: Gia sir A va B la hai ngu6n ket hgrp c6 cung phuorng trinh dao dpng la: U A = U B = Acoscot Xet diSm M bat ky trong moi truong each A mpt doan di va each B mpt doan d2. Phuorng trinh dao dpng t^i M do song tCr A den: ui = Acos(cot - ) Phuorng trinh dao dpng t^i M do song tir B den: U 2 = Acos(cot - ) K Dao dpng t^i M la tong hpp cua hai dao dpng tren. 2nd,, , , - ) + Acos(cot u = u, + U2 = Acos(cot o 7t(d2-d,) u = 2Acos—^^^^ *^cos c o t - 7t(d2 2nd,, -) +d,) V$y dao dpng t^i M la dao dpng dieu hoa voi bien dp : A ^2 A cosTa thay A phy thupc vj tri cua diem M Nhir vay: * T^ii M CO bien dp c\rc d^i - 2A (hai dao dpng thanh phdn ciingpha : = 2kK) khi : cos 7 t ( d 2 - d i ) = 1 o Vay: Tai nhirng diem M c6 hi^u dircmg di b§ng so nguyen Ian birffc song thi bien dao d9ng tong h9rp c^c dai va hpp thanh mpt hp cac duong hyperbol nh?in A va B lam tieu diem (ke ca duong trung tr\rc cua AB). dj - d, = kA, voi k = 0, ±1, ±2,... k = l k =0 k = -l k = -2 k =2 k'=-2 k-=o k'=-l * Tai M CO bien dp c\rc tieu A(p = (2k + l)7t) khi : cos d2 - d , = (k + = 0 (hai dao dgng thanh phan ngu^c pha : 7t(d2-d,) =0 vai k = 0, ±1, ±2,... Vay: Tai nhirng diem M c6 hi|u ducmg di bing mpt so ban nguyen Ian birofc song thi bien dp dao dpng tong hpp cue tieu va hpp thanh mpt hp cac dircmg hyperbol nh^n A va B lam tieu diem. Chuy: DQ l^ch pha cua hai dao d(mg thanh phan la: 27r(d2-di) 2nd A© = = X X Dung dg l^ch pha ta cung c6 the tim ra ditQC cac kit qua nhu tren * Y nghia cua hif n tuyng giao thoa song: Khi c6 hi^n tugng giao thoa xay ra thi CO the ket lu^n doi tugng dang nghien cuu c6 ban chat song. V I L Nhieu xa song: + La hi^n tupng song khi gap vat can se di l^ch khoi phuong truyen thang cua song va di vong qua vat can do. + Hi?n tupng nhieu thoa song. la mpt d§c tinh c6 hiru cua song, giong hi?n tupng giao V I I I . Song am: Khi mgt vgt dao dgng se lam khong khi a ben bj nen roi bi dan, xudt hi^n luc dan hoi trong khong khi vd lam dao dgng nay truyen din cac phan tir khi a xa horn. Dao dgng truyen di trong khong khi tgo thanh song dm. Nhu v$y: + Song am la nhung dao dpng phat ra tir nguon am, dupe truyen qua khong khi vao tai ta lam mang nhT dao dpng gay ra cam giac am. + Song am la nhung song co truyen trong moi truong vat chat (khi, long, An). - Trong chat khi vd chat long song dm la song dgc vi trong cac chdt nay l\K dan hoi chi xudt hi^n khi co bien dgng nen, dan. Song ha am la nhirng song co hpc co tan s6 f < 16 Hz - Song sieu am la nhirng song ca hpc co t^n s6 f > 20 000 Hz - Song am ma tai nguai CO the cam thy dupe CO tan so tir 16 den Hz, con gpi la am thanh. - Trong chdt ran gom cd song ngang vd song dgc vi trong chdt rdn l\rc dan hoi xudt hi^n khi c6 bien dgng l^ch hogc nen, dan. - 20 000 + Sy phan bift song am, ha am va sieu am la do s^r cam thy am cua tai con nguai. Cac song nay co ban chat v^t li giong nhau va giong vai cac song ca hpc khac. 10 * Song am t r u y e n dugc trong tSt ca cac moi truong k h i , long, ran nhimg khong truyen dugc trong chan khong. + Song am truyen di rat kem trong chat xop ; nhung ; bong ; val .... + Trong moi moi truong am dugc truyen d i v a i toe dg xac djnh. * Toe d9 t r u y e n am phu t h u g c : - Tinh dan h6i va khdi lugng rieng cua moi truong. - Nhi$t dg ciia moi truong. Noi C h u n g Vri„ > vi6„g > vwhi Chiiy: Trong chdt rdn song am c6 the Id song ngang hade song dqc. * Nhac am: la nhung song am c6 tan so xac djnh (va thuang keo ddi), c6 do thj dao dgng la nhung duong cong tuan hoan. Vidu : tieng hat, tieng dan... * T a p am: la nhung song am khong c6 tan so xac djnh, c6 do t h j dao dgng la nhung duong cong khong tuan hoan. Vi du: tieng may no IX: Cac dac trimg sinh ly cua nhac i m : * D9 cao cua am: La mgt dac tinh sinh ly cua am, gSn lien v o i tan so am. Am cd tdn so l&n gpi la dm cao hogc dm bong. Am c6 tdn so nhd gpi la dm thdp hodc trdm. A m cang cao khi tan so cang Ion, nhung dg cao ciia am khong t i I9 vai t i n so. * A m sac : Khi mQt ngudn dm phdt ra niQt dm cd tdn sof (dm ca ban) thi cUng dong thai phdt ra cdc hga dm cd tdn so la bQi s6 ciia f. TUy theo cdu trite cua ngudn dm ma cdc hpa dm c6 so li/tpig. bien dp, thai gian ton tgi khdc nhau. Am phdt ra la tong hQp ciia dm ca ban vd cdc hga dm, no cd tdn sd fnhwig duong bieu dien cua nd khdng con la duong sin md tra thdnh mgt duong tudn hoan phirc tap cd chu ki. Moi dgng cua duong bieu dien img vdi niQt dm sdc nhdt djnh. Do dd cdc ngudn dm khdc nhau se tgo ra nhirng dm sac khdc nhau. Vay: + A m sac la mgt d$c tinh sinh l i ciia am giup ta phan bi?t dugc cac am cung dg cao nhung phat ra t u nhiJng nguon khac nhau. + + A m sic dugc hinh thanh dyra tren tan so va bien dg am. A m sac gan lien v a i d6 thi dao dgng am. A m sac khac nhau k h i dang do thj dao dgng am khac nhau. + Cdc nhac cu khdc nhau khi phdt ra dm cd cimg dp cao se cd dgng do thj dao dgng dm vdi tdn so giong nhau nhung cd li dd bien ddi khdc nhau => dd thi dao dgng dm khdc nhau. * Dg to cua am: Nang lu-gng am: Nang lugng am t i 1^ v o i binh phuong bien dg song am. 11 Cirong d9 am I : la nSng lugng ma song am truyen trong mpt don vj thai gian qua mpt don vj difn tich d$t vuong goc vai phuong truyen am. S + Dan vj cua cuong dp am I la W/m^. + Cirang dp am la mpt d$c tinh vat li cua am. Mire cirong dp am L : i + Am thanh nghe cang to khi cuong dp am cang Ian. + Dp to cua am khong ti 1? vai cuong dp am. + Cam giac am tang theo loga ciia cuong dp am. + De so sanh cuong dp ciia mpt am voi cuong dp am tieu chuan nguai ta dung muc cuong dp am L : L = 10lgi(I la cif&ng dm gay ra a tai nguai; I„ la cirang dm tieu chudn) + Don vj mure cuong dp am la Ben (B) hay dexiben (dB) + Muc cuong dp am la mpt d§c tinh v^t li ciia am. Chuy: Am md tai nguai nghe duQC c6 cuong dQ nhd nhdt Id lo Oo gQi Id ctrnng dQ dm chudn). Nguai ta chgn k = 10 ''^ W/m^ Id cuong dp dm chudn cua dm. - Tai nguai phdn bi?t dugc hai dm c6 mice cuong dQ chenh l^ch nhau it nhdt la I dB. - - Am md tai ngitai nghe duQfc c6 ctrong dQ Ion nhdt bdng 10 W/m^. - Muc cuong dQ dm tieu chudn bdng 0 vd muc cuong dQ dm manh nhdt bdng 130 dB (L„ax = lOlg-^ I. = 130 dB) D9 to cua am : la mpt d^c tinh sinh ly cua am, ph\ thupc cuong dp am va tan so am. Dp to cua dm gdn lien v&i muc circmg dp am. \ * Nguon nh^c am : Co hai lo^ii nguon nh^c am chinh : + Day dan hai dau c6 djnh: - Tren day dan se c6 song dung khi chieu dai day la: ^ = k | ( v o i k = l,2,3...)hay ^ - k ^ . - Nhu v^y voi day dan c6 chieu dai £ va c6 dp cang day khong d6i thi ^ ' V song dung xay ra khi tan so f = k — 12 T - Khi kich thich cho day dan dao dgng thl tren day c6 song dCmg va phat ra am CO ban (hay ho^ am b^c 1) umg vai k = 1, ciing cac ho? am b^c 2 ; bac 3 ... ung vai k = 2 ; 3 .. Am tong hgrp la mpt dao dpng tukn hoan phuc t^p CO cung tan so am ca ban (nen moi logi dan c6 dm sac khdc nhau). + 6ng sao (hay ken): - Cau t^o ong sao (hay ken) c6 bp ph^n chinh la mpt ong c6 mpt dSu kin, mpt dau ha. Khi th6i mpt lu6ng khi vao ong thi khong khi trong ong dao dpng va trong 6ng c6 song dung khi chieu dai ong thoa dieu ki^n : l = m- ( v a i m = 1 , 3 , 5 ...)hay ^ - m — . 4 4f - Noi each khac vai ong c6 chieu dai £ thi song dung xay ra khi tan so f=m-:^. - Khi thoi sao thi trong ong sao c6 song dimg va phat ra am ca ban (hay ho9 am b^c 1) umg vai m = 1, cung cac ho? am b?c 3 ; b?c 5 . . . irng vai m = 3 ; 5 .. Am tong hgrp la mpt dao dpng tuan hoan phurc t?p c6 cung tan so am ca ban (nen moi logi sao hogc ken c6 dm sac khdc nhau). - Chieu dai ong cang Ian thi tan so f cua am phat ra cang nho. * Hpp C9ng hirong : la mpt v^t rong c6 kha nang cpng huang vai nhieu tan so am khac nhau d l tSng cuang nhung am do. DAO DONG OIEN TU' SONG DIEN TLF I. M^ch dao d9ng: La mpt m?ch kin gom mpt ty difn c6 di^n dung C m4c noi tiep vai mpt cupn cam L (difn tra ho?t dpng R = 0). M?ch dao dpng ho?t dpng d\ra tren hi?n tupng t\ cam. I I . Syr bien thien cua di^n tich trong m^ch dao dQng : Di^n tich cua t\ dif n trong m?ch dao dpng bien thien dieu hoa vai tan so goc 1 VLC • + Chuki dao dpng rieng: T = 27tVLC + Phuang trinh dao dpng cua di^n tich : q = Qo cos(cot + (p) + Cuang dp dong di^n trong m^ch: i = q' = -coQo sin(a)t + cp) = coQo cos((at +

tir truong va di?n tnrcmg trong m^ch dao dpng tuan hoan. V^y: S\ bien thien tuan hoan theo quy lu^t ham sin ciia i, q va u (ho$c syr bien thien tuan hoan theo quy lu^t ham sin ciia di?n truong va tir truong) trong m^ch dao dpng dugc gpi la dao dpng tg do. III. Dao dpng di^n tir trong mach dao dQng : 1 . Nang lupng di?n truong t^p trung o ty di?n : W m^ch nay gpi la h? t\ dao dpng. 14 VI. Dao dQng dif n tir circrag bu-c - Sir CQng hirong: + MJc mach dao dpng LC c6 tin s6 dao dpng rieng la fo vai mpt nguon di$n ngoai CO di?n ap bien thien dieu hoa: u = Uocos27ift => dong di^n trong mach se bien thien theo tan so f cua di?n ap u chu khong bien thien theo tan so fo nOa. Luc nay dao dpng^ong m^ch la dao dpng cuong buc. + Khi tan so f = fo thi bien dp dao dpng di?n trong m^ch d^t gia trj c\rc dai => trong m^ch c6 cpng huong dif n. Vai di?n tra R cua m^ch cang nho thi bien dp khi cpng huong rat Ian. + Hifn tupng cpng huong di$n dugc umg dyng trong mach Ipc; mach chpn song ; m^ch khuech d^i * Sir tirong tu- gifra dao dyng di?n tir va dao dyng co": GiCra dao dpng di?n tu va dao dpng co c6 syr dong nhat ve hinh thuc (cac phuang trinh va cong thuc c6 cung mpt dang) ma con la syr dong nhat ve quy luat bien doi theo thai gian. VII. Di^n tir trirong: * Hai gia thuyet cua Macxoen (Maxwell): + Trong vung khong gian c6 tir truong bien thien theo thoi gian se xuat hifn trong khong gian do mpt dif n truong xoay. Dgc diem cua di^n truong xoay: Cac dic&ng sire la cac durang cong khep kin baa quanh cac dmmg cam vmg tir. No khac han cac du&ng siec cua tru&ng tinh di^n di ra tic di^n tich duang va di vao di^n tich dm. + Trong vung khong gian c6 di?n truong bien thien theo thai gian se xuat hi?n trong khong gian do mpt tu truong. Ban chat ciia tir truong la cac duomg cam img tir ludn xoay. * Difn tir trucmg : Theo Macxoen: Trong vung khong gian c6 tir truong bien thien theo thoi gian se xuat hifn mpt difn trirong xoay, va c6 difn truong bien thien theo thai gian thi xuat hif n mpt tir truong trong vung do. + Di?n truong hoac tu truong khong the ton tai dpc lap voi nhau. Dif n truong va tir truong la hai mjt the hifn khac nhau cua mpt lo^i truong duy nhat gpi la dif n tir truong. + Truong difn tu la mpt d^ng v^t chat, dong vai tro truyen tuong tac giOa cac difn tich. Tuong tac difn tir Ian truyen trong khong gian voi v^n toe bang v^n toe anh sang . Di4n truong tinh va tir truong tinh la trirong h(/p rieng cua di?n tir truong. VIII. Song di?n tir : Song difn tir la qua trinh truyen di trong khong gian ciia mpt difn tir truong bien thien tuan hoan theo thoi gian. 15 * Song dif n tir + CO v^n toe truyen song difn tir trong chan khong bang v$n toe anh sang c»3.10Ws. + la song ngang. T^i mpt diem bat ky tren phuomg truyen, vecta cuong dp di?n trirong E va vecto cam ung tir B vuong goc nhau va cung vuong goc vai phuang truyen song. Dao dpng ciia di^n truang va cua tu truang luon cung pha vai nhau. XI CO buac song trong chan khong la (vai c la vgn toe dnh sang ;fla tan so cua song di^n tir). + truyen trong moi trirong v$t chat (cac difn moi), va ca tiong chan khong. + CO the cho cac hi^n tupng : phan x^, khiic xa, giao thoa ... va tuan theo cac quy lu^t nay. + CO mang nang lugng. Nha c6 nSng lirpng ma khi song di?n tir truyen den mpt anten, no se lam cho cac electron ty do trong anten dao dpng. Nguon phat song di?n tir la nhijng nguon t^o ra di^n truang ho|ic tir truang bien thien ban dau nhu : tia lira di?n, cau dao ngSt di^n ... Nhung song di^n tu c6 buac song tir vai met den vai kilomet dupe diing trong thong tin lien l^c v6 tuyen nen gpi la cac song v6 tuyen. I X . Mach dao dQng hit - Angten : Trong m?ich dao dpng kin: hau het di^n tu truang biSn thien t$p trung trong ty difn va cupn cam. M^ch khong buc x^ song di?n tu. Trong m^ch dao dpng ha: di$n tir truang vupt ra ngoai mgch t^o ra song di?n tir. Khi cae ban eiia ty di^n l^ch nhau 180° thi kha nang phat song ciia m^ch la Ian nhat. Trong thyc te, nguai ta chi diing mpt day dan dai c6 cupn cam a giira, dau tren de ha va dau duai tiep dat. Day nay gpi la Sngten. Angten la bp ph^n nim a loi vao ciia may thu va a loi ra ciia may phat. Angten la m^ch dao dpng ha. + Nguyen tSe phat song di^n tir dya vao sy birc x^ song di^n tir. + Nguyen tSc thu song di$n tir dya vao sy cpng hirang dif n tir. X . Nguyen tSc truyen thong bSng song di^n tir: Quy trinh chung: + Bien cac am (ho$c hinh anh) thanh cac dao dpng di?n tan so thap, gpi la am tan (ho^c thj tan). + "Trpn" cac dao dpng tren vao song di?n tu eao tan, ta dupe dao dpng di^n duy trl vai tan so cao nhung bien dp thi bien thien theo dao dpng di?n am tan (qua trinh nay con gqi la bien di^u bien dq ) . Song di^n tir da bien dif u (gpi la song mang) sg mang cae tin hif u am tan di xa thong qua anten phat. 16 + Dung anten de thu song di?n tir cao tan. + M^ch chpn song mic vai anten tren se chpn Ipc de thu song di?n tir muon thu (m^ich nay la khung dao dgng LC va ho^t dgng d^ra tren s\f cpng huomg difn). + Dung m^ch tach song cao tan va am tan. + M^ch khuech d^i dao dpng am tan nh^n dugc va loa phat am nh^n dugc. XI. Song di^n tir va thong tin v6 tuyen: + Song dai (buac song A> 1 km): it bj nuoc hap thu nen dugc dCing de thong tin duai nuoc. + Song trung (bir&c song X tir 100 m den 1000 m) : ban ngay bj tang di^n l i hap thy m^nh nen khong truyen di xa dugc ; ban dem bj tang di?n li phan x?i nen truyen di xa dugc. + Song ngan (biroc song A tir 10 m den 100 m): co nang lugng Ion va it bj khong khi hap thy, bj phan x^ lien tiSp nhieu l£in giua tang di?n li va m§t d4t. Cac dai phat song ngan cong suat Ion co thk truyen song nay di mgi noi tren mjt dat. ! + Song cu-c ngan (btr&c song X tir 0,01 m den 10 m) : co nSng lugng 1cm nhat, khong bj tang di^n li hap thy hoSc phan x?, co kha nang truyen di rat xa theo duong thing va dugc dung trong thong tin vu try. Dai truyen hinh dung cac song eye ngin. Song nay khong truyen dugc xa tren m^t dat, phai diing cac dai tiep song trung gian ho$c cac v^ tinh nhan t^io de thu song cua dai phat roi phat tra ve trai dat. Cac dai phat thanh thuong dung song trung, song ng4n va ca song eye ng§n (dai FM). DONG DIEN XOAY CHII^U I. Cach tao dong dif n xoay chieu (Dif n ap dao d^ng dieu hoa): . Dya vao hi?n tugng cam ung di?n tir Cho mgt khung day dan di^n tich S va co N vong day, quay deu quanh mgt tryc I doi xung xx' ciia no trong mgt tir truong deu B ( B vuong goc voi xx') vai v ^ toe goc CO. Theo djnh lu^it cam ung d i | n tir, trong khung xult h i | n mgt suat dif n dpng cam ung: e = EoCOs(CL)t + cpo) V | y : Suat difn dgng trong khung biln thien dieu hoa vai tan so goc co va gay ra a hai dau khung mgt difn ap xoay chieu: u = UoCOS (cot + cpu) + Khi noi m^ch tieu thy vao di^n ap xoay chieu u = UoCOs(cot + cpu) thi trong m^ch CO dong di^n xoaygbicu i , ~ IoCO3((0t i khi i = lQCOs(a>t + 9;) thi U R = UoRCOs((Ot + 9 j ) voi UQR = I Q R * Gian do vecto O I I I . Doan mach xoay chieu chi c6 di^n : * Dung kbang: Z(- = —^ voi C la di?n dung cua ty toC 18 * Lien hf Uc va i : Di^n ap giua hai dau doan mach chi c6 ty di^n bien thien di^u hoa cung tan so nhung tre pha hon dong di?n ^ => khi i = Iocos(cat + (Pj) t h i = Uoccos(tot + tpj - •^) v a i U o c ~ ^o^c * Gian do vecta O Uoc IV. Doan mach xoay chieu chi c6 cu9n thuan cam : * C a m khang: * Lien = Leo v a i L la dp t y cam cupn day. u va i : Difn ap giua hai dau do^n m^ch chi c6 cupn cam bien thien dieu hoa cung tan so nhung som pha hon dong di^n => khi i = Iocos(cot + 9 ) ) thi . = UoLCOs(cot + 9 1 + ^ ) ^^ri U Q L = IQ^^L Gian do v e c t a : UOL o V. Doan mach xoay chieu R L C : Gia sir dong di?n xoay chieu qua do^n m^ch la: i = lo coscot => UR = UoR coscot v a i UOR = loR UL = U o L C O s ( c o t + ^ ) vai UOL = I O Z L Uc = U o c C O s ( o ) t - ^ ) v a i Uoc = IoZc Di?n ap giira hai dau doan m^ch A B la: u = UR + U L + U c => * Uo = UOR + UoL + Uoc Quan giira dif n ap va dong dif n: Tir gian do vec ta, ta c6 : Ug = ^ U O = IO7R-+(ZL-ZC)' yj^l^ +(UOL ~^OC)^ (1) 19