TYPES OF CURRENT

DIRECT CURRENT

DC (direct current) is the unidirectional flow or movement of electric charge carriers (which are usually electrons). The intensity of the current can vary with time, but the general direction of movement stays the same at all times. As an adjective, the term DC is used in reference to voltage whose polarity never reverses.

ALTERNATING CURRENT

In electricity, alternating current (AC) occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement. Household utility current in most countries is AC with a frequency of 60 hertz (60 complete cycles per second), although in some countries it is 50 Hz. The radio-frequency (RF) current in antennas and transmission lines is another example of AC.

The variation of any electrical parameter over a period of time (in this case the electric current) is an electric signal.

The tension or voltage of domestic electricity is an alternating signal because it alternates between possitive and negative values. Its waveform is also sinusoidal, with a smooth, regular shape.




THE EFFICIENCY OF ALTERNATING CURRENT

The average power of alternating current is equal to the direct current that is needed to produce the same effect. In the case of an alternating sinusoidal current, the aveerage power would be as follows;

Vef=Vmax/√2

TRANSFORMERS

There i an important different between alternating and direct current. Alterning current  can be increased or decreased by a transformer.
Transformes consist of to windings made of copper wire. If we apply an alternating current to one of them (V1), it will produce a certain voltage in the other (V2). The value will depend on the number of times that the copper wire has been wrapped around each winding, represented as "n1" and "n2":

V1/V2=n1/n2