To depict electric field in space, surrounding the battery, you can use the vectors of tension (rice. 15.3). This method of images is time consuming and not always convenient. Faraday has offered to draw the field lines of force, in the future we will call lines of tension. One of these lines is drawn through the point As well, that the vector E is directed along. Having in this way a number of direct from the charge q, get a picture of the field lines of tension (rice. 15.4).

To distinguish between the images of fields of positive and negative charges, line tension is considered aimed in the wrong direction, where indicates the vector of intensity E. Then the fields of positive and negative charges will be different in the direction of the lines of tension (rice. 15.4).

More difficult to draw the line tension, when the field created by several charges, for example, two. To draw a line so, to the intensity vectors, shown at each point, entirely lay on it, in most cases, cannot. But it is always possible to draw a curved line so, vectors of tension were everywhere tangent to it. One such line drawn through a point M in figure. 15.5, showing the field strength vectors of the two equal opposite charges. (Think, why through each point of the field in this way can only be placed on one line.)

So, the line of tension called a line, at each point where the electric field vector is directed along the tangent. In figure. 15.6 and 15.7 lines of tension shows the fields are equal in magnitude with opposite and like charges.

Graphically depicting the field, remember, the lines of electric field intensity:

1. never intersect each other;
2. have start on the positive charge (or in infinity) and end on negative (or in infinity), t. e. lines are open;
3. between charges anywhere are not interrupted.

The field pattern, the drawn lines of tension, will be better, if you agree to draw these lines thicker there, where the field strength is more.

So, the density of the lines of intensity should be proportional to E. In the calculations conventionally considered, through unit area of the surface, perpendicular to lines of tension, passes the number of lines, which is numerically equal to E in the place, where is this surface. (Think, where on the rice. 15.6 and 15.7 tensions and more directed as the intensity vector in three randomly selected fields on each of the drawings.)