ABSTRACT
The key to understanding and solving a.c. circuits, whether they are series circuits, parallel circuits or even three-phase circuits, is your ability to sketch a phasor diagram which represents that circuit and, then, use this phasor diagram to generate all the equations you need, simply by treating it as a simple exercise in geometry or trigonometry. 'Real' a.c. circuits, then, are relatively complicated because they contain a combination of resistance, inductance and capacitance. So, in order to understand the behaviour of an a.c. circuit, it is necessary to start by considering how an 'ideal' circuit would behave. So if, at resonance, the vector sum of a circuit's inductive reactance and capacitive reactance is zero, leaving only its resistance to oppose current, then it follows that the circuit's current will reach its maximum value at resonance.
