If the electric field generated by charge Q, placed another charge Q0, it will affect him with a certain force. This feature is called the electric field strength E. It is the ratio of the force F with which the field acts on positive electric charge Q0 at a certain point in space, to the value of this charge: E = F/Q0.
Depending on the specific point in space, the field strength E can change what is expressed by the formula E = E (x, y, z, t). Therefore, the electric field vector refers to the physical quantities.
Because the field strength depends on the force acting on a point charge, the electric field intensity vector E is the same vector of force F. According to Coulomb's law, the force with which the two interacting charged particles in vacuum is directed along the straight line which connects the charges.
Michael Faraday suggested that clearly depict the field strength of the electrical charge with lines of tension. These lines coincide with the intensity vector at all points on a tangent. In the drawings, they are denoted by arrows.
In that case, if the electric field is uniform and the vector of the tension constant in its module and direction, the lines of tension parallel with it. If the electric field created by positively charged body, the line tension pointing away from him, and in the case of negatively charged particles towards it.