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# Introduction

Electrical charges can be positive or negative. Charges of the same type repel each other, and charges of different types attract each other. For example, static electricity can cause hair to stand on end as similarly charged strands of hair all try to avoid each other, while in lightning a build up of negatively charged electrons moves rapidly to a region of positive charge.

Electrically charged particles exert forces on each other at a distance, that is they don’t need to be touching each other. When these charged particles are stationary the force is referred to as electrostatic, and is described by Coulomb’s law. Coulomb’s law was established experimentally in the late eighteenth century, and is one of the building blocks of the theory of classical electromagnetism.

This course has four parts: a brief introduction to Coulomb’s law in vector form, a video demonstration of an experiment, an exercise and a video solution. This gives you a practical demonstration of electrostatic forces and the opportunity to practise using the vector form of Coulomb’s law. You will also be encouraged to think about the assumptions you make in your calculations and possible sources of experimental uncertainty.

Learning outcomes

After studying this course, you should be able to:

- describe the properties of Coulomb’s law and electrostatic force
- determine the force exerted on one stationary charge by another using Coulomb’s law
- explain some of the uncertainties and errors that can occur in experimental measurements of electrostatic properties.

This OpenLearn course is an adapted extract from the Open University course SM381 Electromagnetism.

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OpenLearn - Electromagnetism: testing Coulomb’s law
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