y2 ^2 Thay a = -cox vao bieu thufc t r e n t a c6: — + — = A^ CO CO Vdy chgn dap an B Cdu 41: M o t song a m t r u y e n t r o n g thep v6i toe 5000 m/s Neu lech pha cua song a m d h a i d i e m g a n n h a t each m t r e n cung mot phifOng t r u y e n song l a ^ t h i t a n so cua song bang: A 1000 Hz B 1250 Hz C 5000 Hz D 2500 Hz Ta eo: A® = t - = - => X = 4d = 4.1 = m T a n so cua song: f = - = X, Vdy chgn dap an B = 1250Hz 2.10 Cau 42: T L T thong qua mot vong day d i n la O = — ,-2 cos 1007rt + - (Wb) 71 4J - Bieu thufc cua suat dien dong cam ufng xuat h i e n t r o n g vong day l a : A e = 27csinl007rt (V) (V) B e = - s i n 1007rt + V C e = -2sinl007it (V) D e = 2sin 1007rt + - (V) V Giai = 2sin 1007rt + dt Vdy chgn dap an D Ta c6: e = Cdu 43: D a t dien ap u = (V) cos ^ 0 ; r t - (V) vao h a i dau n i o t t u d i e n 2.10"^ ' CO dien dung — (F) O thori diem dien ap giufa h a i dau t u d i e n la n 150 V t h i CLTcfng dong dien t r o n g raach la A Bieu thufc cua ctfdng dp dong dien t r o n g mach l a : A i = 5cos 1007rt + - (A) C i = 4V2cos 1007rt + Gi4i Chi ti^t de thi TS DH, CD M6n VSt li (A) B i = 4>/2cos D i = 5cos lOOTrt lOOTrt (A) (A) 45