Hướng dẫn giải chi tiết đề thi tuyển sinh đại học, cao đẳng môn vật lí phần 2 tờ số (27)

Ta c6: cO|.co, = o>o LC Giai = Zci = ZL2 C0,t02 T - U.T Suy r a : R ' = UV2 U„ U + (ZLI - Zci)' V (©i - = (ZLI - ZLS)' = 0)2)' Suy r a : R = L ( { O i - © ) = — 200JI = 160(Q) 5;i Vay chgn dap an C Cdu 28: D a t d i e n ap u = Uocoscot vao h a i dau doan mach gom dien t r d t h u a n R, cuon c a m t h u a n c6 tif c^m L va t u dien c6 dien dung C mac n o i t i e p Goi i l a CLTorng dong dien tufc thcfi t r o n g doan mach; u i , U v a U I a n Ixiqt l a d i e n ap tufc thori giufa h a i dau dien tror, giffa hai dau cuo a c a m v a giufa h a i dau t u dien; Z l a tong tror cua doan mach He thufc diing l a A i = U3CoC B i = - ^ C i = - ^ R D i = - coL Z Giai V i pha cua U R c h i n h l a pha cua i n e n chia di/cfc Vay chon dap an B Cdu 29: D a t d i e n ap u = 400cosl007it (u t i n h bang V , t t i n h bang s) vao h a i dau doan mach A B gom dien tror t h u a n 50 Q mac n o i tiep v d i doan mach X Cifcfng dong dien hieu dung qua doan mach l a A B i e t of thofi d i e m t , d i e n ap tufc t h d i giufa h a i dau A B c6 gia t r i 400 V; d thcfi d i e m t + — ^ (s), cUcfng dong d i e n tufc thcfi qua d o a n m a c h bSng 400 k h o n g v a dang g i a m Cong suat t i e u t h u dien cua doan mach X l a A 400 W B 200 W C 160 W D 100 W Giai T a c : U = 0 V V ; I = 2A + Of thofi d i e m t , u = 400V ^ + Of thcfi d i e m t + I (p„ = Ikn ^ n ^ = ^' ^ang g i a m => cp', = — + 2kn + t a i thc;i d i e m t : (D: = — - — + 2kn ^ ' 162 ' Giai Chi t i e t d i t h i T S D H , CBMon Vat li + goc lech pha giiJa u va i : Acp = cp - cp = - — + Cong suat: P = U.I.cosAcp = 400W Vay chgn dap an A Cau 30: Mot chat diem dao dong dieu hoa tren true Ox Vector gia toe cua chat diem c6 A I6n cUc dai or vi t r i bien, chieu luon hifdrng bien B \dn cifc tieu qua vi t r i c^n bSng luon cung chieu vdri vectcf van toe C Idrn khong doi, chieu luon hifdng ve v i t r i can bang D lorn t i le vdi lom eua li do, chieu luon hiJdrng ve vi t r i can bang Giai Mot chat diem dao dong dieu hoa tren true Ox Vectcf gia toe cua chat diem c6 Idfn t i le vdri Idrn eua l i do, ehieu luon hi/drng ve v i tri can bang Vay chgn dap an D Cau 31: Hai chat diem M va N eo eCing khoi iMng, dao dong dieu h6a cung tan so doc theo hai dtfcfng thang song song ke va song song vdri true toa Ox V i t r i can bang cua M va cua N deu d tren mot difcfng thang qua goc toa va vuong goe vdri Ox Bien cua M la cm, cua N la cm Trong qua trinh dao dong, khoang each Idrn nhat giufa M va N theo phtforng Ox la 10 cm Moc the n^ng t a i v i t r i can bkng O thdi diem ma M c6 dong nang bang the' nang, t i so dong nang cua M va dong nang cua N la A.I B.I C.^ 16 D.li Giai Taco: MN^ax= ^ + ^ « 10cm Chat diem M c6 dong nang bang the nang t h i chat d'^em N cung eo dong nang bang the nang: 1,.2 Taco- ^ ^ ( M ) _ - ^ ^ V _ • W,(N) l l j ^ 64 16 2'2 ^ Vay chgn dap an C Cau 32: Tai Ha Noi, mot may dang phat song dien tii Xet mot phifang truyen c6 phiforng thang dufng hiTdrng len Vao thcfi diem t, tai Giai Chi tiet de thi T S D H , C D iVISn Vat li 63 diem M t r e n phirofng t r u y e n , vector cam ufng tCf dang c6 I6n cifc dai va hLfdrng ve p h i a N a m K h i vectof ctfcfng dien trifdng c6 A I d n C L f c d a i va hifdng ve phia Tay B Idfn c\Sc d a i va hiidfng ve phia Dong C I6n bang k h o n g D I d n C L f c d a i va hiTdng ve phia Bac GiSi Bac Nam Chon dap an A Cdu 33: Chieu x i e n tCr k h o n g k h i vao ntfdc m o t chum sang song song r a t hep (coi nhiT m o t t i a sang) gom ba t h a n h p h a n dcfn sSc: do, l a m va t i m Goi r^, , rt Ian li/dt l a goc khuc xa ufng v d i t i a mau do, t i a m a u l a m va t i a m a u t i m He A = rt = rd B rt < thufc dung l a < rd C rd < < rt D rt < rd < Giai Neu chiet suat be t h i goc khuc xa I d n : sini = n.sinr Cung goc t d i i , m a nd < < nt t h i rt < < rd Vdy chqn dap an B • Cdu 34: Cac h a t n h a n ddteri ^H, t r i t i |H, h e h He c6 nSng li/dng lien k e t Ian liiOt la 2,22 MeV; 8,49 M e V va 28,16 MeV Cac h a t nhan tren diTdc sap xep theo A thuf ttr g i a m d a n ve ben vOfng eua h a t n h a n la B ; H , ; H , ^He lUc, D ] H , ^He, i H C ^He, ^ H , ^H Giai N a n g l i i d n g l i e n k e t r i e n g cua cac h a t n h a n dcfteri ^ H , t r i t i ] H , h e l i ^He I a n lUdt Ik 1,11 MeV; 2,83 MeV; 7,04 MeV N a n g liidng l i e n k e t r i e n g c^ng I d n t h i h a t cang ben vQ'ng Vdy chgn dap an C 64 GiSi Chi tiet de thi TS DH, CB Mon VSt li ... bien, chieu luon hifdrng bien B dn cifc tieu qua vi t r i c^n bSng luon cung chieu vdri vectcf van toe C Idrn khong doi, chieu luon hifdng ve v i t r i can bang D lorn t i le vdi lom eua li do, chieu... t h i chat d'^em N cung eo dong nang bang the nang: 1, .2 Taco- ^ ^ ( M ) _ - ^ ^ V _ • W,(N) l l j ^ 64 16 2' 2 ^ Vay chgn dap an C Cau 32: Tai Ha Noi, mot may dang phat song dien tii Xet mot... t n h a n ddteri ^H, t r i t i |H, h e h He c6 nSng li/dng lien k e t Ian liiOt la 2, 22 MeV; 8,49 M e V va 28 ,16 MeV Cac h a t nhan tren diTdc sap xep theo A thuf ttr g i a m d a n ve ben vOfng