Electric Fields

• Electric charges create an electric field
• An electric field is created around any electrically charged object
• The closer to the object you get, the stronger the field is and vice versa
• You can show an electric field around an object using field lines. E.g. you can draw the field lines for an isolated (not interacting with anything), charged sphere:

  • Electric fields lines go from positive to negative
  • They're always at a right angle to the surface
  • The closer together the lines are, the stronger the field is

  
• Charged objects in an electric field feel a force
• When a charged object is placed in the electric field of another object, it feels a force. This force causes attraction or repulsion
• The force caused by the electric fields of each charged object interacting with each other
• The force on an object is linked to the strength of the electric field it is in
• As you increase the distance between the charged objects, the strength of the field decreases and the force between them gets smaller
• Two oppositely charged particles

  (check image)

  • The electric field of Q interacts with the electric field of q.
  • This causes forces to act on both Q and q
  • These forced move q and Q closer together

  A) Q

  B) q

  
• Sparking can be explained by electric fields
• Sparks are caused when there is a high enough potential difference between a charged object and the earth (or an earthed object)
• A high potential difference causes 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 (known as ionisation)
• Air is normally an insulator, but when it is ionised it is much more conductive, so a current can flow through it. This is a spark