Types of current
Direct current
Between the terminals of a battery, there is a continuos, stable flow of energy. If we use a voltmeter to measure the current in a car battery, the result will always be 12 volt. This is called direct current.--

Alterneting current
 Alternating current occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement.
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 analternating signal because it alternates between positive and negative values. Its waveform is alsosinusoidal, with a smooth, regular shape.--


The efficiency of alterning 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 average power would be as follow: Vef = Vmax /√2 
 

Transformers
Transformers consist of two 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

EFFECTS OF ELECTRIC CURRENT

The movements of electrons though conductive
materials produces effects that have useful
application.

HEAT:The energy that an electric current 
produces as heat is called the Joule Effect.
Formula: E=|x|xRxt


LIGH:
There are various ways that electricity
can be used to produce ligh.


Incandescent bulbs: When an electric current
passes through the metallic filament of a 
light bulbs, it produces light.


Fluorescent tubes: There is a metallic 
filament, normally made of tungsten.
An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow.


Light-emitting diode(LED):is a semiconductor device that emits visible light when an electric current passes through it. The light is not particularly bright, but in most LEDs it is monochromatic, occurring at a single wavelength.