In that region, the fields from each charge are in the same direction, and so their strengths add. The field is stronger between the charges. (This is because the fields from each charge exert opposing forces on any charge placed between them.) (See Figure 4 and Figure 5a.) Furthermore, at a great distance from two like charges, the field becomes identical to the field from a single, larger charge.Figure 5b shows the electric field of two unlike charges. While the electric fields from multiple charges are more complex than those of single charges, some simple features are easily noticed.įor example, the field is weaker between like charges, as shown by the lines being farther apart in that region. The field is calculated at representative points and then smooth field lines drawn following the rules outlined in the text.įigure 4 shows how the electric field from two point charges can be drawn by finding the total field at representative points and drawing electric field lines consistent with those points. Two positive point charges q 1 and q 2 produce the resultant electric field shown. This impossibly lengthy task (there are an infinite number of points in space) can be avoided by calculating the total field at representative points and using some of the unifying features noted next.įigure 4.

To find the total electric field due to these two charges over an entire region, the same technique must be repeated for each point in the region. The total electric field found in this example is the total electric field at only one point in space.

In cases where the electric field vectors to be added are not perpendicular, vector components or graphical techniques can be used. (See Figure 2.) The electric field strength is exactly proportional to the number of field lines per unit area, since the magnitude of the electric field for a point charge is E=krac\ Note that the electric field is defined for a positive test charge q, so that the field lines point away from a positive charge and toward a negative charge. A test charge placed anywhere will feel a force in the direction of the field line this force will have a strength proportional to the density of the lines (being greater near the charge, for example). The closeness of the lines is directly related to the strength of the electric field. (b) In the standard representation, the arrows are replaced by continuous field lines having the same direction at any point as the electric field. (a) Arrows representing the electric field’s magnitude and direction. Two equivalent representations of the electric field due to a positive charge Q. Field lines are essentially a map of infinitesimal force vectors.įigure 1. Figure 1b shows numerous individual arrows with each arrow representing the force on a test charge q. Figure 1b shows the standard representation using continuous lines.

(We have used arrows extensively to represent force vectors, for example.)įigure 1 shows two pictorial representations of the same electric field created by a positive point charge Q. Like all vectors, the electric field can be represented by an arrow that has length proportional to its magnitude and that points in the correct direction. Since the electric field has both magnitude and direction, it is a vector.

Draw the electric field lines between two points of the same charge between two points of opposite charge.ĭrawings using lines to represent electric fields around charged objects are very useful in visualizing field strength and direction.Describe an electric field diagram of a positive point charge of a negative point charge with twice the magnitude of positive charge.Calculate the total force (magnitude and direction) exerted on a test charge from more than one charge.By the end of this section, you will be able to:

Magnitude of electric flux formula