A volume in which there are forces acting on electric charges, is called an electric field. Such a field is created by the separation charges with different marks as a result of appropriate mechanical, chemical, thermal or light activities. Accumulation of homonymous electric charges between which there are electric field, is called electrodes or poles (positive or negative, depending on the mark). Direct cause of separation of positive or negative particles is called electromotive force inducing the voltage and expressed in volts. An apparatus or device in which is what it’s called a source of tension. In order to characterize the degree of influence of different fields on the point electric charge q the concept of electric field strength shall apply. It shall be marked with the letter E and measured in volts per metre (V/m). The force F acting on this charge in the electric field shall be expressed by the formula
There is an electric field strength of different value and direction at different points in the field. Lines drawn from one pole of the field to another (between points of different potential), tangentially to the direction of the field strength at subsequent points, are called force lines. Where they thicken, the field strength is greater. If there are free electric charges in an electric field, they move along the force lines, the faster the greater the field strength.
