Inductors in series and parallel

A coil has inductance, measured in henries. The values of inductance used in radio range from several henries (H) to parts of a microhenry (µH). The inductance of a coil depends on the number of turns and the core details.
When inductors are connected in series, the number of turns is effectively increased. So too is the inductance, and the effective inductance of the circuit is the sum of the individual inductances.
These calculations apply only to inductors which are not coupled magnetically. Where there is coupling between coils, the total inductance is also affected by the amount of coupling.
As with the resistor, for amateur radio examination purposes, you can visualise the resulting value of inductors like this:

Putting two inductors in series in effect increases the number of turns so the inductance value increases.

Putting two inductors in parallel, in effect decreases the effective inductance

Like the resistor, we can use visualised examples to easily work out what happens with two (or more) typical inductors of the same value. Put two in parallel, the value will halve. Put two in series and the effective inductance value will be double.
In a perfect inductor there is no loss of energy. The energy is stored in the magnetic field surrounding the inductor and (in an AC circuit) it changes in magnitude and sign twice in each cycle. The opposition to the flow of current is called the inductive reactance and is denoted by XL. Reactance is an opposition to current resulting from a storage of energy. The relationship is:
XL = 2p f L where f is the frequency in hertz, L is the inductance in henries, and XL is the reactance expressed in ohms.Note that as the frequency rises, the inductive reactance also rises.
In practice there is no such thing as a perfect inductor and it is usual to consider the practical component to be a circuit containing both a resistor R (the inductor's resistance) and L the inductor.

Where resistance and inductance (inductive reactance) exist in a circuit together, they are combined into a term, called impedance, representing their combined total opposition to current flow.
Reactances can be added together directly. But resistances and reactances must be added together vectorially (as vectors), to get impedance.