User:Inconspicuum/Physics (A Level)/Electric Field

Electric field E is the force per. unit charge caused by an electric field:

$$E_{electric} = \frac{F_{electric}}{q}$$

The unit of electric field is NC-1 or Vm-1.In general, the electric field is the rate of change of electric potential (voltage) with respect to distance:

$$E_{electric} = -\frac{dV_{electric}}{dx}$$

Special Cases
There are two different types of field which you need to know about. Uniform fields occur between two plates with opposite charges. Here, the electric field is simply:

$$E_{electric} = \frac{V_{electric}}{d}$$

A charged sphere also has an electric field. To gain a formula for this, we divide the formula for force around a charged sphere by q, so:

$$E_{electric} = \frac{Q}{4\pi\epsilon_0r^2}$$,

where &epsilon;0 = 8.85 x 10-12C2N-1m-2.

The electric field around a point charge is called a radial field. The field strength is highest at the centre and decreases as the distance from the centre increases. This is reflected in the above formula, which shows that Eelectric is proportional to $$\frac{1}{r^2}$$.

Field Lines
We can represent electric field using field lines. These go from positive charge to negative charge. They are more closely packed together when the electric field is stronger. In a uniform field, they look like the following:



Around two oppositely charged spheres (known as a dipole), they look like the following: