I. Two charge classifications - positive and negative

    A. Negative charges (electrons) are usually the charges that are mobile.

    B. Units of charge: Coulombs

    C. Magnitude of electron charge = 1.6 x 10-19 C

II. Coulomb's Law

    A. Magnitude of force exerted on one charge by another

                      F = keq1q2/r2

        where q1 and q2 are the magnitudes of two charges separated by a distance r and ke is a constant.

         (ke is approx. 9 x 109 N-m2/C2)

    B. Recall: Forces are vectors!

III. What are conductors and insulators?


1. A 3.00 microcoulomb point charge is 0.12 m away from a -1.5 microcoulomb charge. What is the force on each charge?

2. Two point charges (+1.0 microcoulomb, -3.0 microcoulomb) are 0.10 m apart. Where should a third charge be placed so that it is in electrostatic equilibrium?