DIRECT CURRENT
Current intensity is made
up of quantity of charge
divided by unit of time:
Where:
I is current intensity, measured
in Ampère(A);
ΔQ is quantity of charge, whose
unit of measurement is
Coulomb(C);
Δt is the unit of time, measured
in seconds (s).
In electronics we call direct current (or
DC) a current that is stable in direction
and intensity in the unit of time
Electronic circuits
An electronic circuit is composed by
conductors and a generator (a device
capable of mantaining the same
potencial difference in time). It can be:


A series circuit, in which we find the
same current into the conductors;
A parallel circuit, in which we find the
same potencial difference.
Some simple circuits
First Ohm's law
The first Ohm's law states that current is directly
proportional to potencial difference and inversely
proportional to the resistance:
The unit of measurement of resistance is Ohm (Ω, V/A)
RESISTORS
They are devices which hold by the first Ohm's
law and they can be bond in:


Series, in which the equivalent resistance is
equal to the sum of all the resistances;
Parallel, in which the inverted equivalent
resistance is equal to the sum of the inverted
resistances.
Kirchhoff's laws
Propieties of an ohmic circuit are expressed in
Kirchhoff's laws. The first law can be applied to
junctions (points in which three or more
conductors join). The second law can be
applied to loops(pieces of circuits composed by
branches, which connect two junctions).


Kirchhoff's junction rule: the sum of current
intensities entering a junction equals the
sum of the leaving ones;
Kirchhoff's mesh rule: the sum of potencial
differences in the mesh equal to zero.
Electromotive Force

It's the ratio between work (W) he does to move a
charge q inside of it and the charge itself.
While an ideal generator creates an
electromotive force that equals the
potencial difference to the ends, a
real one generates less potencial
difference, that equals the formula:
Second Ohm's law

The second Ohm's law states that
resistance of a conductor is directly
proportional to his lenght and inversely
proportional to his area
In which:
ρ is resistivity (it depends on the materials of the
conductors);
l is the lenght of the conductor;
S is the surface