capacitors

What is a capacitor

A capacitor consists of 2 metal plates separated by a dielectric

What is capacitance

The amount of charge stored on the capacitor for every 1V of potential difference

What happens to a capacitor when connected across the terminals of a battery?

One side gains a positive charge and the other gains a negative charge

What is a dielectric?

Insulating material placed between capacitor plates

Purpose of dielectric

Increase capacitance of a capacitor

How does using a dielectric increase the capacitance

• between the oppositely charge plates there is an electric field

• we know E=V/D so V=ED where v is the potential difference across the capacitor and d is the distance between the plates

• Dielectrics reduce the magnitude of the field, therefore reducing pd between plates

• This reduces capacitance as C=Q/V

How do dielectrics reduce the magnitude of the field between the plates

• the polar molecules in the dielectric rotate so the positive side faces the -ve plate and visversa

• Therefore polar molecules produce their own electric field in the opposite direction to the one between capacitor plates

• This field has a smaller magnitude than the one between plates

• Therefore resultant force between plates reduced

What is the increase in capacitance when a dielectric is added (isolated capacitor)

The capacitance increases by a factor of