Here are some of the necessary equations, values, and laws that one must memorize or quickly derive in order to achieve success on the AP-Physics C E & M exam:
E=(K/r^2)(integral from v to infinity of dq)
Gauss's Law: Net flux= integral over the closed surface of EdA = Q/(epsilon not)
The force exerted by one point charge on another acts along the line between the charges. It varies inversely as the square of the distance separating the charges and is proportional to the product of the charges. The force is repulsive if the charges have the same sign and attractive if the charges have opposite signs.
Rules for Electric Fields:
1. Electric field lines begin on positive charges (or at infinity) and end on negative charges (or at infinity).
2. The lines are drawn uniformly spaced entering or leaving an isolated point charge.
3. The number of lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge.
4. The density of the lines (the number of lines per unit area perpendicular to the lines) at any point is proportional to the magnitude of the field at that point.
5. At large distances from a system of charges with a net charge, the field lines are equally spaced and radial, as if they came from a single point charge equal to the net charge of the system.
6. Field lines do not cross. (If two field lines crossed, that would indicate two directions for E at the point of intersection.)
Depending on the conductor, if it is a shell, solid or hollow, different values of E will be obtained by the properties of the conductor and the radius given in the problem.
That is the condensed version of the necessary things to know for electrostatics.