To understand such circuits, you must learn some additional terms.

Frequency (f): It is the number of cycles per second measured in Hertz (Hz)

Peak Value: It is the maximum value of ac voltage or current.

RMS value: Root Mean Square (RMS) value is the value of effective voltage or current and is ~70% of the peak value. The voltage value of 230 Volts quoted for domestic supply is actually a RMS value.

Power Factor: When voltage and current in an AC supply reach their maximum and zero value at the same time, they are said to be ‘in phase’. When this is not the case, some of the energy is lost thereby reducing the actual power available. Power Factor expresses the ratio between these two states.

Power Factor (PF) = (Active Power in Watts) / Apparent Power in volt-amperes.

Some useful websites and video resources, listed with self explanatory titles, cover important concepts about circuits from a basic to an advanced level.

**Non-resonant and resonant circuits **

According to Ohm’s Law, current (I) and voltage (V) in a circuit are proportional to each other. Such circuits are called linear circuits. The ratio between voltage and current is the resistance (R), the value of which does not depend upon Frequency (f).

However, the value of this ratio does depend upon frequency. Impedance (Z) is the term used to represent ratio of voltage and current when these are not ‘in phase’. Resistance can be considered as a special case of Impedance.

If the voltage and current are out of phase by 90°, the ratio of voltage to current is called the Reactance (X).

Electrical resonance can occur in an electrical circuit when the impedance between the input and output of a circuit is minimum (almost a zero). Such circuits can generate higher voltage than their input. The frequency at which resonance occurs is called the resonance frequency. Value of this frequency is determined by inductance, capacitance and impedance of the AC circuit.

Resonant circuits are widely used in wireless transmission networks.

**RLC Circuits **

An RLC circuit comprises a resistor (R), Inductor (L) and a capacitor (C) and hence the name RLC. Similarly, other combinations are RL and RC. These circuits are used as oscillators, filters and tuners.

In an RLC circuit, there is large voltage across the inductor and the capacitor while the resistance is low. However, these large voltage values almost cancel each other giving a small total voltage. In this case, it is therefore possible to produce a large voltage with a small voltage source.

Some useful websites and video resources, listed with self explanatory titles, cover important concepts about resonance in AC circuits from a basic to an advanced level. The video resources include practical construction of a RLC circuit.