﻿ Electric field

# Electric field

When we answered the question of where the electric forces of two charged particles would be balanced, we introduced a tiny positive test charge to find the answer. After all, the electric force needs two charges by definition. Here, we will use that same concept to introduce a new quantity, the electric field.

We can define the electric force of charge q on charge q' and let q' be a positive tiny test charge. The direction of the force is away from the test charge.

If we divide through by the charge q' we can define a new quantity, the electric field. This force per charge can be defined anywhere whether there is actually a charged particle present or not. A field is constructed of a quantity that can be defined at any point. The electric field is a vector field. At every point in space, the magnitude and direction of the field can be determined.

The electric field of a positive point charge is shown here. We can measure the force per charge at each point in space that would exist if there was a tiny test charge there. We assume the test charge is tiny so it does not affect the field we are measuring. By convention, we use a positive test charge. The direction of the field is away from the positive test charge.

Sometimes we connect the force vector arrows to depict the field in another way, as electric field lines. The direction of the field lines has the same convention as the electric field vectors. The denser the field lines, the stronger the magnitude of the electric field.

The electric field is the force per charge. For a group of point charges, the E field vectors add, just like the electric force vectors.