§ 7-5 The phasor（ 相量）
A sinusoidal current or voltage at a given frequency is
characterized by only two parameters,an amplitude and a phase
angle,The complex representation of the voltage or current is
also characterized by these same two parameters.
)()c o s ( ???? ???? tjmm eItIi
the current response:
)(2)c o s (2)c o s ( ?????? ?????? tjm IetItIi
??? ???? ItIi )co s (2
??? 0co s2 ??? VtV
A time representation A frequency domain(频域 )
representation
The phasor,?? ???? ?? IIVV 0
??? s i nco s jIIII ?????
j
1?
?I
? cos I
? sin I
?
VVVtt ??? 3010 0)3040 0c os (210 0)( ?????? ?
AIt
Atti
??
?
605)603 7 7co s (25
)1 5 03 7 7s i n (25)(
?????
??
?
VttVV )45c os (2115)(45115 ?? ?? ???????
AttiAI )6/c o s (21.7)(6/1.7 ??? ??????
Example: