Coulomb’s Law Class Exercises
AP Physics
1. What is Coulomb’s Law?
2. Compare Coulomb’s Law to the Law of Universal Gravitation. How is the electric force like the
gravitational force? How is it different?
3. a) What is the electric force between an electron and proton separated by 0.0529 nm?
b) What is the electric force if you replace the proton with 2 protons? (What element would that be?)
4. a) What is the electric force between a +3.0 C charge and a +5.0 C charge separated by 1.0 m?
b) What is the electric force if you move the charges so that they are 0.5 m apart?
5. A positive and negative charge experience an electric force when they sit at a certain distance from
each other.
a) How will the electric force between them change if the charge on the negative object were doubled?
b) How will the electric force between them change if you were to double the distance between the two
charges?
6. Two positive charges sit a particular distance apart from each other.
a) How is the electric force between the charges affected if you triple the charge on one object and
double the distance between the two objects?
b) How is the electric force between the charges altered if you double both charges and triple the
distance between the two objects?
7. Three point charges are arranged in a line. A –5 C charge is placed in the center, a 3C charge is
placed 1 m to the left and a –2 C charge is placed 2 m to the right, as shown in the diagram.
a) What is the net force on the –2 C charge? (Ignore any forces except the electrical force)
b) What is the net force on the 3 C charge?
8. An arrangement of point charges is laid down on a table: first, a +6 mC charge is placed on; then a
–3 mC charge is placed 75 cm to the east of the first charge; finally, A +8 mC charge is placed 1 m to
the east of the second charge.
a) What is the net force on the –3 mC charge?
b) What is the net force on the 8 mC charge?
9. A +1 mC charge sits 10 m to the south of a –7 mC charge and 5 m to the west of a +3 mC charge.
a) What is the net force on the 1 mC charge?
b) What is the net force on the 3 mC charge?
10. A helium atom consists of two electrons orbiting around a nucleus consisting of two protons (which
are REALLY close together and act like a single charge). At one instant, one of electrons is 0.027 nm
above the nucleus and the other is 0.049 nm to the left of the nucleus.
a) What is the net force on the nucleus at this moment?
b) What is the net force on the upper electron at this moment?