7.4.2

# Parallel Plate Capacitor

Test yourself

## 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

• 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

• 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.
• $C=A{{\epsilon}_0}{{\epsilon}_r}/d$

### 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.