Lines of Force

LINES OF FORCE

The electric field lines or lines of force are helpful in visualizing field patterns. They provide the following basic information:

1. The direction of the field is along the tangent to a line of force.
2. The strength or magnitude of the field is proportional to the number of lines that cross a unit area perpendicular to the line.

The electrostatic field lines have the following properties

1. They always start on positive charges and end on negative charges.
2. The number of lines that originate from or terminate on a charge is proportional to the magnitude of the charge.
3. Lines of force never cross because field cannot be in two directions at the same point.
4. Field lines always meet a conducting surface normally.

Note that the lines are crowded together where the field is strong and spread far apart where number of lines passing through a unit area are normal to the field direction.

Suppose N lines emerge from an isolated point charge. At a distance r from the charge the lines are spread over a spherical surface of area 4πr2. Thus, the density of lines is N/4πr², and decreases as 1/r².

This is exactly the way the field strength varies according to equation (1.5).