Let any point in space is a point electric charge q (rice. 15.1). Then at each point of the environment on the test charge will operate electric power. Therefore, the field around the charge is sometimes called force field.

Power, acting on the same test charge at various points in an electric field, vary in size and direction (rice. 15.1). Therefore, it is advisable to type the special power characteristics of any point of the field, created by electric charge. As you can see from Coulomb's law, force F that can be developed, as for the same point of the field this force is directly proportional to the magnitude of the test charge q_PR;

F=Eq_PR (15.1)

The proportionality factor E in the formula (15.1) remains constant for each point of the field and can serve as a power characteristic that point. Power characteristics of the point of the electric field E is called a field. It is measured by, with which the field acts on a unit positive charge, included in the set point field.

The field strength is the vector, the direction of which coincides with the direction of the force F, acting on the positive charge q_PR at a given point of the field, and the module of this vector is determined by the ratio

E= F/ q_PR. (15.2)

From (15.2) you can display the unit of the strength of E in C:

E= 1N/1Кл=1H/C=1 kg*m/ (And*³).

The SI unit of electric field intensity take tension in such point of the electric field, in which the charge, equal 1Кл, a force of 1N).

The electric field is determined by the size and location of those charges, which create this field, and for each point can be calculated theoretically. Show, how can this be done to a secluded field of point charge q. For the force of interaction of point charges (q and q_PR) have:

From (15.3) you can only find the numeric value of the vector E, he aimed along the line, connecting the selected point of the field from a point charge q, and coincides with the direction of the force, acting on a positive test charge. If the field created by several charges, the intensity E at any point of the field is as a geometric sum of intensities, created at this point by each charge separately (rice. 15.2).