You may have noticed that certain forces can act on objects even when they are not touching. Take gravity for instance. The Earth and the moon do not touch each other (thank goodness!) but the force of gravity keeps the moon in orbit. The electrostatic force acts in this way also. The are around any charged object is known as that object's electric field.
We can quantitatively determine the strength of a electric field. We begin by imagining a large charged object.
Now bring an object with a charge of the same polarity, but smaller magnitude, close to the first charge.
The strength of the electric field at the location of the particle is the force
that is acting on the second charge divided by that charge. So if we have a third charge, identical to the
second, and we bring it closer to the large object, then the force on that particle will be greater, and
we know that the electric field in that region is greater. We represent this with the equations:
E is in newtons per coulomb, F is in newtons, q is in coulombs.
We can also substitute Coulomb's Law into this equation to obtain:
E = k (a special constant) * charge / the square of the distance between the charges
k = 8.9875*109 N*M2/C2
The principle of superposition holds for electric fields. The electric field of a group of charges is equal to the vector sum of their electric fields.
We often want to visualize the shape of an electric field. To do this, we use electric field lines.
These lines tell us two things about the electric field: