Ten friends telling you their weights on Planet Zug will not help you figure out your own weight, even if you happen to know your mass. However, if they tell you the value of "g," the acceleration due to gravity, you can easily figure out how much you would weigh if you visited Zug.
Fg = mg -or- g = Fg / m This means "g" is the force per kilogram, or the force each kilogram of matter would experience while in that spot. "g" is the value of the gravitational field.
Similarly, the Electrostatic Field, E, tells you the force acting on each Coulomb of charge.
Fe = q E -or- E = Fe / q Where q is the amount of charge placed in the field.
For a spherical source, when you put Coulombís Law in place of the electrostatic force, the electric field becomes:
††††††††††††††††††††††††††††††††††† E = kQsource†††††† where Q is the source, or cause of the electric field
††††††††††††††††† ††††† r2
Some rules for electric fields:
1. Arrows showing electric fields always show the direction of the force on a positive test charge placed in that field. It also shows the direction the positive test charge would move if allowed to.
11. Field lines never cross, since they show the net force caused by the source charges on a test charge.
111. Field lines point away from positive sources and towards negative sources.
IV. Field lines which are close together show a stronger field; field lines which are spread out show a weaker force.
V. Electric fields are forces per charge; since forces are vectors, so are fields. You must add them by breaking them into components if more than one field acts on the same location.
Here are (in order left to right) the field lines radiating from a positive source, the field lines moving away from two positive sources, and field lines moving from a left-hand positive source to a right-hand negative source.