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Coulomb’s Law

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Coulomb's Law

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Coulomb’s Law


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Learners explain and apply Coulomb’s law in given cases

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Describe electrostatic force.
  • Explain the effects of the magnitude and sign of charged particles on electrostatic force.
  • Explain the effects of the distance between charged particles on electrostatic force.
  • State Coulomb\'s law.
  • Give real-life examples of how Coulomb\'s law is applied.

Everything You'll Have Covered

Coulomb's law is one of the most fundamental concepts in electrostatics. In the late 18th century, Charles Coulomb showed that when two charged particles interact, each particle will exert a force on the other. Coulomb demonstrated that the electrostatic force between two charged particles is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. This means that the magnitude of the electrostatic force decreases very rapidly as the distance between the charges increases. For example, if the distance between two charged particles is increased by a factor of 2, the force would be only of its original value (i.e. divided by 4). The force may be either attractive or repulsive depending on the sign of the charges.

Two particles with different signs will attract, while those with the same sign will repel. When first studying the electric force, the charges are usually considered to be point charges, meaning they have zero mass. A point charge may be thought of as a tiny sphere with charge distributed over its surface. This is a good first order approximation for protons, electrons, and neutrons.

Electrostatic force is a vector quantity; so it has both a magnitude and a direction. The magnitude of the force may be found using the following equation where k is known as the electrostatic force constant and is related to the dielectric constant of the medium in which the particles are present. For simplicity, the medium may be considered a vacuum, where k is then given by where is thepermittivity of free space (a vacuum) given by The absolute value signs indicate that the sign of each charge is dropped prior to carrying out the computation. The direction of the force depends on the sign of the charges and the geometry of the problem.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Define the electrical charges, Explain interaction between the electrical charges
Course Physics
Type of Tutorial Concept Development
Key Vocabulary Coulomb, Coulomb’s law, dielectric constant