The direction of the force on one point charge due to another is either directly toward the other charge (if the charges have opposite signs) or directly away (if the charges have the same sign).
The electric field(symbol E) is the electrical force per unit charge. It is a vector quantity.
If a point charge q is located where the electric field due to all other charges is E, then the electric force on the point charge is
Fe = qE
(16-3b)
The SI units of the electric field are N/C.
Electric field lines are useful to represent an electric field.
The direction of the electric field at any point is tangent to the field line passing through that point and in the direction indicated by the arrows on the field line.
The electric field is strong where field lines are close together and weak where they are far apart.
Field lines never cross.
Lines start on positive charges and end on negative charges.
The number of lines starting on a positive charge (or ending on a negative charge) is proportional to the magnitude of the charge.
The principle of superposition says that the electric field due to a collection of charges at any point is the vector sum of the electric fields caused by each charge separately.
