Electric fields and field lines

​​In a nutshell

An electric field is created around any electrically charged object. Electric field lines are used to illustrate the electric field surrounding a charged object.

Electric fields and field lines

The closer to a charged object you get, the stronger the field. The further away you are from a charged object, the weaker the field. Field lines are used to illustrate the electric field around an object.

For an isolated, charged sphere, the radial field lines have the following properties:

• Electric field lines go from positive to negative, as indicated by the arrows.
  
• Electric field lines are always perpendicular to the surface of the sphere.
• The closer together the lines are, the stronger the field is.
• As you go further away from the charged sphere, the field lines are further apart, which indicates the field is getting weaker.

Forces due to electric fields

When a charged object is placed within the electric field of another object, it experiences a force. This force can either be attractive or repulsive. The force arises because the electric fields of each object are interacting with each other, based on both the strength of the fields and the distance between the objects.

Uniform fields

The field between two parallel plates, one positive and the other negative, would be a uniform field. The field lines of a uniform field are straight, parallel, and point from positive to negative.

Sparking

Sparks are generated when there is a large enough potential difference between a charged object and the earth. A large potential difference creates a strong electric field between the charged object and the earthed object.

The strong electric field causes electrons in the air particles to be removed, which is known as ionisation. Air is usually an insulator, however when it is ionised it is much more conductive, so current is able to flow through it. This is how a spark is generated.