An electric field can be represented by imaginary lines to indicate the direction and magnitude of the electric field. The density is a measure of the strength of the electric field at that point (the field lines are close together where the field is strong and far apart where the field is weak). The direction of an electric field line at any point is the direction in which a positive charge would move if placed at that point. Field is always directed from the positive charge toward a negative charge, as shown in Figure 1.

Figure 1

The magnitude field lines have the following properties:

1. The electric field lines indicate the direction of the electric field (the field points are at a tangent to the field line at any point).

2. Electric field lines start from a positive charge and end on a negative charge.

3. The number of lines representing the strength of the electric field.

4. The direction of the electric field lines indicating the direction of the electric field.

5. Electric field lines never cross or intersect each other.

6. In a conductor, the electric field lines are perpendicular to a surface and are located outside of the conductor's surface.

The electric flux through an area is defined as the number of electric field lines multiplied by the area (A) perpendicular to the electric field (Φ_E):

E = Φ_E / A or

Φ_E = E A …………………………. (2-2)

If the surface under consideration is not perpendicular to the electric field lines as shown in Figure 2, then the electric flux:

Φ_E = E A cos θ ………………….. (2-3)

Figure 2

Where A = small virtual area inside the electric field

E = electric field

θ = angle between E and A.