13.3. The Coulomb Force Law http://www.ck12.org
13.3 The Coulomb Force Law
The Coulomb Force Law states that any two charged particles(q 1 ,q 2 )— with charge measured in units of Coulombs
— at a distancerfrom each other will experience a force of repulsion or attraction along the line joining them equal
to:
~Fe=kq^1 q^2
r^2The Coulomb Force [1]Where
k= 8. 987 × 109 N·m^2 ·C−^2. The Electric ConstantThis looks a lot like the Law of Universal Gravitation, which deals with attraction between objects with mass. The
big difference is that while any two masses experience mutualattraction, two charges can either attract or repel each
other, depending on whether the signs of their charges are alike:
Like gravitational (and all other) forces, Coulomb forces add as vectors. Thus to find the force on a charge from an
arrangement of charges, one needs to find the vector sum of the force from each charge in the arrangement.
Example 1
Question: Two negatively charged spheres (one with− 12 μC; the other with− 3 μC) are 3m apart. Where could you
place an electron so that it will be suspended in space between them with a net force of zero (for this problem we
will ignore the force of repulsion between the two charges because they are held in place)?