CIE A Level Physics (9702) 2019-2021

Revision Notes

21.2.3 E Fields v G Fields

E Fields v G Fields

  • Electric field strength (E) and gravitational field strength (g) have very similar equations
  • Despite a few differences, they are analogous to one another in many ways
  • Origin of the force:
    • G fields: Mass M
    • E fields: Charge Q
  • Field strength:
      • G fields:

    E Fields v G Fields equation 1

      • E fields:

    Electric Field Definition equation 1


  • Field strength due to a point mass/charge
      • G fields:

    Deriving Gravitational Field Strength (g) equation 4

      • E fields:

    Electric Field of a Point Charge equation

  • Potential:
    • G fields: Work done in bringing a unit mass from infinity to that point
    • E fields: Work done in bringing a unit charge from infinity to that point
  • Potential of a point mass/charge:
      • G fields:

    E Fields v G Fields equation 2

      • E fields:

Electric Potential Due to a Point Charge equation

The sign depends on the charge

  • Potential energy:
    • G fields: G.P.E = Mɸ
    • E fields: E.P.E = QV
  • Force in a radial field:
    • G fields: Always attractive
    • E fields: Attractive for a negative charge, repulsive around a positive charge

Exam Tip

This topic could come up as long structured answer question, practice summing up this information as you would for a 6 mark question.

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