Electric Fields (SQA National 5 Physics): Revision Note

Electric field effects

• An electric field is defined as:

A region of space in which an electric charge experiences a force

• The direction of an electric field at a point is defined as:

The direction of the force on a positive charge at that point

• Charged objects create electric fields around themselves

  • This is similar to how magnets create magnetic fields

• An electric field is a vector quantity as it has both magnitude (size) and direction

Electric fields around charges

• Electric field lines are

  • used to represent the direction and magnitude of an electric field

  • always directed from the positive charge to the negative charge

• Where field lines are closer together, the field is stronger

• Where field lines are further apart, the field is weaker

Electric field between two parallel plates

• The electric field between two parallel plates is a uniform electric field

• The field lines are:

  • directed from the positive to the negative plate

  • parallel

  • straight lines

Electric field lines between two oppositely charged parallel plates

Electric field around a point charge

• Around a point charge, the electric field lines are directly radially inwards or outwards:

  • If the charge is positive (+), the field lines are radially outwards

  • If the charge is negative (-), the field lines are radially inwards

Electric field lines near positive and negative point charges

Electric field between two point charges

• For two opposite charges:

  • the field lines are directed from the positive charge to the negative charge

  • the closer the charges are brought together, the stronger the attractive electric force between them becomes

Electric field lines between two opposite charges

• For two charges of the same type:

  • the field lines are directed away from two positive charges or towards two negative charges

  • the closer the charges are brought together, the stronger the repulsive electric force between them becomes

  • there is a neutral point at the midpoint between the charges, where the resultant electric force is zero

Electric field lines between two like charges