18.1.1—An electric field is an example of a field of force and define electric

An electric field is a region in which a charge experiences a force; field strength E is force per unit positive charge.

Use a small positive test charge to define direction, then calculate force on any charge with its sign included.

Between parallel charged plates, a positive charge feels force in the field direction and a negative charge opposite it.

The field exists without placing a test charge, and field direction is not always the same as force on a negative charge.