9478 / 2027

Chapter 14

Electric Fields

Choose the source, test charge, direction and reference before using an electric-field or energy equation.

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Choose a lesson

  1. Point-charge force and field

    Distinguish a source field from the force on a test charge and use charge signs with Coulomb's law.

  2. Electric potential and energy

    Use an infinity reference and distinguish potential per charge from the signed interaction energy of a pair.

  3. Field from a potential gradient

    Use a local tangent and its negative sign, and distinguish vector field sums from scalar potential sums.

  4. Uniform fields between plates

    Calculate a plate field from perpendicular separation and determine force directions for signed charges.

  5. Charged-particle motion

    Connect electric force to component acceleration, a calculated exit state and subsequent force-free motion.

  6. Capacitance and plate charge

    Define capacitance, distinguish plate-charge magnitude from net charge, and interpret a linear Q-V record.

  7. Energy stored in a capacitor

    Derive stored energy from the V-Q area and compare changes at fixed charge or fixed voltage.

Syllabus coverage

This chapter covers Electric Fields, topic 14(a-k), in the 9478 syllabus (2027).

Explain electric interactions with consistent signs and use field and energy models to calculate motion and capacitor behaviour.

Point-charge force and field, electric potential and pair energy, potential gradients, uniform plate fields, charged-particle deflection, capacitance and stored energy.

View the learning outcomes
14(a)
Recall and use Coulomb's law for the force between two point charges in free space or air. Point-charge force and field
14(b)
Recall and use the inverse-square electric field of a point charge in free space or air. Point-charge force and field
14(c)
Define electric potential by external work per unit small positive test charge brought from infinity. Electric potential and energy
14(d)
Use the point-charge electric potential with its stated reference and source sign. Electric potential and energy
14(e)
Explain and calculate the electric potential energy of a system of two point charges. Electric potential and energy
14(f)
Recall and apply electric field strength as the negative local potential gradient. Field from a potential gradient
14(g)
Calculate a uniform parallel-plate field from potential difference and perpendicular separation. Uniform fields between plates
14(h)
Calculate the force on a charge in a uniform electric field. Uniform fields between platesCharged-particle motion
14(i)
Describe the effect of a uniform electric field on charged-particle motion. Charged-particle motion
14(j)
Define capacitance as charge stored divided by potential difference and apply C = Q/V. Capacitance and plate charge
14(k)
Use the area under a potential-difference-versus-charge graph and all three equivalent linear-capacitor energy expressions. Energy stored in a capacitor