5. Strength of electric field

Electric field

Coulomb’s Law describes forces acting at a distance between two charges. We can reformulate the problem by breaking it into two distinct steps, using the concept of an electric field.

  • Think of one charge as producing an electric field everywhere in space.
  • The force on another charge introduced into the electric field of the first, is caused by the electric field at the location of the introduced charge.

If all charges are static, you get exactly the same answers with electric field as you do using Coulomb’s Law. So, is this going to be just an exercise in clever notation? No. The electric field concept comes into its own when charges are allowed to move relative to each other. Experiments show that only by considering the electric field as a property of space that propagates at a finite speed (the speed of light), can we account for the observed forces on charges in relative motion. The electric field concept is also essential for understanding a self-propagating electromagnetic wave such as light. The electric field concept gives us a way to describe how starlight travels through vast distances of empty space to reach our eyes.If the idea of force “acting at a distance” in Coulomb’s Law seems troublesome, perhaps the idea of force caused by an electric field eases your discomfort somewhat. On the other hand, you might also question if an electric field is any more “real”. The reality of an electric field is a topic for philosophers. In any case, real or not, the notion of an electric field turns out to be useful for predicting what happens to charge.We introduce electric field initially with static charges to ease into the concept and get practice with the method of analysis.

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