The effective value of any periodic current is equal to the value of the direct current which flowing through a resistance R, delivers the same power to r as periodic current does

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

We define the ratio of the phasor voltage to the phasor current as impedance

8-2 Superposition, source transformation and Thevenin's theorem Superposition:

《电路》（英文版）9-1 Instantaneous power

We assume=Im cos(t+a)i=Im cos(ot+B) The phase angle by which the voltage leads

Example 2: (p175-12) resistor, capacitor, and voltage source=100cos300n are all in series. If the average power dissipated by the resistor is 150W and the rms capacitor voltage is 10v, determine R and C

Frequency characteristics(Xi, xc,x,z, y, o vs o Z=R+A=R+(L+Xc)=R+ilo I

A current i at Li produces an open circuit voltage u,at L2s dyal

An ideal transformer is a useful approximation of a very tightly coupled transformer in which the coefficient of coupling is almost unity and both the primary and secondary inductive reactance are extremely large in comparison with the terminating impedance