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Parallel Plate Capacitor

Physics: AQA A Level, topic 7.4.2

Parallel Plates

A parallel plate capacitor is made of two charged plates separated by a distance. This type of capacitor creates a uniform field.

Dielectrics

Dielectrics

  • A parallel plate capacitor has a gap between the two plates, this gap can be filled with air or a dielectric.
  • A dielectric is a material which increases the capacitance of a capacitor.
  • The dielectric allows a capacitor to store more charge.
Capacitance

Capacitance

  • The capacitance of a parallel plate capacitor depends on the distance between the plates, the area of the plates and if there is a dielectric. This relationship can be shown with the following equation:
  • Capacitance = area × permittivity of free space × permittivity of dielectric ÷ distance between the plates.
  • C=Aϵ0ϵr/dC=A{{\epsilon}_0}{{\epsilon}_r}/d
Polar molecules

Polar molecules

  • A molecule is made up of a positive nucleus and a negative electron cloud.
  • In a field, the positive nucleus will move slightly in the direction of the field and the negative cloud will move slightly in the other direction.
  • This creates an imbalance in the charge distribution.
  • If this polarized molecule is then put into a field the cloud will be pulled in one direction and the nucleus pushed in the other.
  • This will cause a rotation.

Test yourself on Parallel Plate Capacitor

  • What is the correct equation for the capacitance of a parallel plate capacitor?

  • Which statements about parallel plate capacitors are true?

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