i(t)=C I leads v by 90 f 2y cos(at +9) ,(-90 COS (-900)+jsi(-90)= i=√2Icos(or+p) I cos( at leads by-90° -C√2sin(or+9) j一-- impedance(2) oC =C√2cos(at+9+90° I∠q=joCV∠9 capacitor reac tance (容抗) 1=jack JoC： C i + − C • I + − • V dt d i t C  ( ) = I = jCV • • I = jCV • • • = = − I C I j j C V   1 1  I leadsV by 90 • • ( ) 1 − − −impedance  C j  • I • V capacitor reac tance C − − −  1 （容抗） 2 cos( ) 2 cos( )      = + = + i I t i f V t e j j j = − + − = − − cos( 90 ) sin( 90 ) ( 90 )     − 90 • • V leads I by 2 sin( ) 2 cos( )      = − + + C V t I t =  C 2V cos(t + + 90)