Capacitance Flashcards
(15 cards)
Define capacitance
Capacitance is the charge stored by a capacitor per unit potential difference
What does a capacitor do
It’s an electrical component that stores charge
What is a capacitor made up of
2 parallel conducting plates with a gap between them separated by a dielectric
What is a dielectric
An insulating material
What forms between plates of a capacitor
A uniform electric field
How does a uniform field form between the plates of a capacitor
When the capacitor is connected to a power source, opposite charges build up on the two parallel plates, which causes the electric field to form
Define permittivity
The measure of the ability to store an electric field in the material
How do you calculate relative permittivity
Find the ratio of the permittivity of the dielectric to the permittivity of free space
Describe what a dielectric is made up of
Polar molecules that align themselves with the electric field present
Why does potential difference to charge a capacitor decrease
- each molecule has its own electric field
- which opposes the field formed by the capacitor, so reduced its field
- so potential difference required to charge the capacitor decreases
What does the strength of a molecule’s electric field depend on
The dielectric’s permittivity
What effect does a decrease in potential difference have on capacitance
A decrease in potential difference causes an increase in capacitance
How do you determine the electrical energy stored by a capacitor from a graph
Find the area under a graph of Q against V
What does the area under a graph of Q against V represent
The electrical energy stored by the capacitor
