Each electric charge surrounds an electric field. As a result of long-term studies, physicists have come to the conclusion that the interaction of charged bodies occurs due to the electric fields surrounding them. They are a special form of matter, which is inextricably linked with any electric charge.
The study of the electric field is carried out by introducing small charged bodies into it. These bodies are called "test charges." For example, a charged cork ball is often used as a test charge.
When a test charge is introduced into the electric field of a body with a positive charge, a light positively charged cork ball will deflect under its action the more, the closer we bring it to the body.
When moving a test charge in an electric field of an arbitrary charged body, one can easily find that the force acting on it will be different in different places.
So, when placing successively at the same point in the field different positive test charges q1, q2, q3, ..., qn, one can find that the forces acting on them, F1, F2, F3, ..., Fn are different, but the ratio of force to size a certain charge for such a point of the field invariably:
F1 / q1 = F2 / q2 = F3 / q3 = ... = Fn / qn.
If we study different points of the field in this way, we get the following conclusion: for each individual point in the electric field, the ratio of the magnitude of the force acting on the test charge to the magnitude of such a charge is constant and independent of the magnitude of the test charge.
It follows from this that the magnitude of this ratio characterizes the electric field at its arbitrary point. The value that is measured by the ratio of the force acting on the positive charge located at this point in the field to the size of the charge is the electric field strength:
E = F / q1.
It, as can be seen from its definition, is equal to the force that acts on a unit of positive charge placed at a certain point in the field.
The intensity of the field acting on a charge the size of one electrostatic unit with a force of one dyne is taken as a unit of electric field strength. Such a unit is called an absolute electrostatic unit of tension.
In order to determine the electric field strength of any point charge q at an arbitrary point of field A of a given charge spaced apart from it by a distance r1, it is necessary to put a test charge q1 at this arbitrary point and calculate the force Fa that acts on it (for vacuum).
According to Coulomb's law :
Fa = (q1q) / r²₁.
If we take the ratio of the magnitude of the force that affects the charge to its value q1, then we can calculate the electric field strength at point A:
Ea = q / r²₁.
In addition, one can find the tension at an arbitrary point B; it will be equal to:
Eb = q / r²₂.
Therefore, the electric field strength of a point charge at a certain point in the field (in vacuum) will be directly proportional to the size of the given charge and inversely proportional to the square of the distance between this charge and the point.
The field strength acts as its power characteristic. Knowing it at an arbitrary point on the field E, it is easy to calculate the force F acting on the charge q at a given point:
F = qE.
The electric field is a vector quantity. The direction of tension at each specific point in the field will be combined with the direction of the force acting on the positive charge placed at the point.
When the field is formed by several charges: q1 and q2, the intensity E at any point A of this field will be equal to the geometric sum of the intensities E1 and E2 created separately at this point by charges q1 and q2.
The electric field strength at an arbitrary point can be displayed graphically with the help of a directed segment, which comes from this point, similarly to the image of force and other vector quantities.