

§ 3 The electrostatic field. Intensity of Electrostatic field
and characterizes the electric field at the point where the test charge. This value is called the intensity and is a power characteristic of the electrostatic field. The field intensity is a vector quantity which is numerically equal to the force acting on a unit positive point charge is placed at a given point of the field
The direction of the intensity vector coincides with the direction of the force.
§ 4 The principle of superposition of fields. The lines of force vector Determine the value and direction of the field produced by a system of fixed charges q_{1}, q_{2}, …q_{n}. Net force , exerted by the field on the test charge q, is the vector sum of the forces , applied to it by each of the charges q_{i}
Dividing by q, we obtain
Principle of superposition (overlay) fields: Intensity of resulting field created by a system of charges, equal to the geometric (vector) sum of the field intensities produced at this point each of the charges separately.Electrostatic field can be represented very clearly with lines of Intensity or power lines of vector . Field line intensity vector is a curve whose tangent at every point in space coincides with the direction of the vector . The principle of construction of power lines :
3. For a quantitative description of the vector Å field lines carried out with a certain density. The number of lines of intensity running through the unit area perpendicular to the lines of intensity must be equal to the modulus of a vector .
Homogeneous is a field that has a vector in any point in space is constant in magnitude and direction, ie vector parallel to the field lines and their density is constant at all points
Inhomogeneous field Homogeneous field
Painting lines isolated point charges
§ 4 'Dipole. Dipole moment. Dipole field Electric dipole is a system of two pointof opposite charges (+ and ) at a distance ℓ. Vector along the dipole axis (the line passing through the two charges) from the negative to the positive charge and is equal to the distance between them, called the ARM dipole. . vector
coinciding with the direction of the dipole arm and the product of the charge q on the arm is called an electric dipole moment or dipole moments .
By the principle of superposition the field intensity Å of dipole at any point
 field generated by a positive charge,  the field of negative charge.
because
Triangle A'B'C 'similar to the triangle ABC, as equilateral and three angles are equal, so
The picture of the dipole field lines:
