Resistors in AC Circuits

In an AC circuit, assuming the voltage across the resistor is described by a sinusoidal wave (as shown in Equation 2.37), the current through the resistor, based on Ohm s law, is 

As can be seen in Equation 2.39, both IR(t) (the current through the resistor) and VR (t) (the voltage across the resistor) have the same frequency and phase. According to Equation 2.38, we have 

Since there is no angular difference between the current in a resistor and the voltage across it, we have 

In a sinusoidal AC circuit, the current through a pure capacitor leads the voltage drop across this capacitor by 90°. The 90° phase relationship between Ic ( ) (the current through the capacitor) and Vc ( ) (the voltage across the capacitor) can be written as 

---