Electric Fields (OCR A Level Physics)

Revision Note

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Defining Electric Fields

  • A charged object creates an electric field around itself
    • This is similar to the way in which magnets create magnetic fields
  • An electric field can be defined as:

A region where an electric charge experiences a force

  • If other charges enter the field then they will experience an electric force, attracting or repelling them from the object
    • Since force is a vector, the direction of this force depends on whether the charges are the same or opposite
  • The force is either attractive or repulsive
    • Recall that opposite charges (positive and negative) charges attract each other
    • Conversely, like charges (positive and positive or negative and negative) repel each other


Electric fields are due to charges. The field around a charge gives rise to an electric force

Point Charge Approximation

  • For a point outside a spherical conductor, the charge of the sphere may be considered to be a point charge at its centre
    • A uniform spherical conductor is one where its charge is distributed evenly

  • The electric field lines around a spherical conductor are therefore identical to those around a point charge
  • An example of a spherical conductor is a charged sphere
  • The field lines are radial and their direction depends on the charge of the sphere
    • If the spherical conductor is positively charged, the field lines are directed away from the centre of the sphere
    • If the spherical conductor is negatively charged, the field lines are directed towards the centre of the sphere

Point charge field lines, downloadable AS & A Level Physics revision notes

Electric field lines around a uniform spherical conductor are identical to those on a point charge

Exam Tip

You might have noticed that the electric fields share many similarities to the gravitational fields. The main difference being the gravitational force is always attractive, whilst electrostatic forces can be attractive or repulsive.

You should make a list of all the similarities and differences you can find, as this could come up in an exam question.

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Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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