Gi^i Chon v i t r i can b k n g l a m goc toa T a i t = 0, v a t d v i t r i can bang PtiLfcfng t r i n h dao dong c6 dang x = A sin cot Trong m o t chu k i , c6 khoang thcfi gian ma gia toe k h o n g vi/tft qua V„,ax = lOOcm/s^ T T Goi t la thofi diem de a - lOOcm/s^, t a c6 4t = — =5> t = — 12 (2n ) 2K T 47i"f "Asia = 100 Ta c6: a — co'Asm — t = 100 T 12 «47r'f'Asin- = 100 f= 100^r' =-^.5.0.5 = « l(Hz).- Vdy chgn dap an C Can 41: T r o n g giof hoc thiTc h a n h , hoc sinh mac n o i t i e p m o t quat dien xoay chieu vdfi d i e n trof R r o i mAc hai dau doan mach vao dien ap xoay chieu c6 gia t r i hieu dung 380 V B i e t quat d i e n c6 cac gia t r i dinh mufc: 220 V - 88 W va k h i boat dong diing cong suat d i n h mufc t h i lech pha giOfa dien ap or hai dau quat va cUorng dong dien qua no la , vdfi coscp = 0,8 De quat dien chay dung cong suat d i n h mufc thi R bang: A Q B Q C Q D 180Q Giai CcTcfng dong dien dinh mufc qua quat: = P 88 U coscp 220.0,8 = 0,5(A) U Ta CO coscp = —'-^ => U , ^ = 0,8 220 = ( V ) U Vi U