Coulomb's Law

Definition

Coulomb's Law states that the force between two charged objects is directly proportional to their charges and inversely proportional to the square of their distance apart.

Key Equations

$F = k \frac{{|q_1q_2|}}{{r^2}}$

• $F$ is the force between charges,
• $q_1$ and $q_2$ are the magnitudes of the charges,
• $r$ is the distance between the centers of the two charges,
• $k$ is Coulomb's constant $(8.987 \times 10^9 \, \text{Nm}^2/\text{C}^2)$.

Problem Solving Tips

• Always express charges in Coulombs and distances in meters to maintain consistency with the unit system.
• Remember that forces are vectors. When multiple charges are involved, vector addition may be needed to find the net force.
• Pay attention to the signs of the charges; like charges repel, and unlike charges attract.

Relevant Experiments

• Measuring the force between charged objects at varying distances gives empirical evidence supporting $F \propto 1/r^2$.
• Using charge sensors and force meters, one can quantify the relationship between charge magnitude, distance, and force, confirming Coulomb's Law.
• Experiments using a torsion balance are classic methods to demonstrate Coulomb’s Law, similar to how Coulomb originally explored the law.

Related terms

Electric Force:

Electric force refers to the attractive or repulsive force between charged objects.

Inverse Square Law: Inverse square law states that some physical quantity or strength is inversely proportional to the square of the distance from the source.

Electric Field Strength: Electric field strength measures the force experienced by a unit positive charge placed in an electric field.