# A bit of theory...

An electric charge creates an electric field in the space surrounding it. When a second charged particle approaches the first, it reacts with it, indirectly, through the fields created by both particles.

The accepted unit of charge, from the SI (International System), is the Coulomb (C) which, compared to the charge of an electron (-1.60219E-19 C), is fairly high.

We can obtain the configuration of an electric field created by a charged particle by calculating the force at several points on a unit charge (or test charge) Q.

```                     F
E =  ---    (newton/coulomb)
q
```

The electric field is in the same direction as that of the force acting upon a positive test charge or in the opposite direction as the force acting on a negative test charge. In this manner the field lines (or lines of force) are directed from positive charges to negative charges. The electric field produced by a charge Q is:

```                         Q
E = --------------  iR
4*(pi)*E0*R²
```

where

Q = value of the static charge creating the field.
R = distance from the charge
E0 = is a constant approximatly 8.854E-12 C²/Nm²
iR= The unit vector uniting the two points under consideration.

We can apply the principle of superpositon to the electric field. In this manner, to calculate the electric field of a system of charges at a given point, we first calculate the field of each charge in that point and do the summation:

```         Q1                       Q2                              Qn
E = --------------  iR1  +  ---------------  iR2  +  ...  +  --------------  iRn
4*(pi)*E0*R1²            4*(pi)*E0*R2²                    4*(pi)*E0*Rn²
```

A way of visualizing an electric field is to spread grass seeds over a liquid, like oil, and a place two electrodes (a positive and negative) into the oil. You will see the seeds align with the electric field.

As a note, in the experience described above as in this computer simulation, we obtain a transversal view of the field which is in reality three-dimensional.