10. Capacitors Flashcards
What does a capacitor consist of?
Two metal plates which are separated by an insulating layer (dielectric)
State three examples of a dielectric?
- Air
- Plastic
- Paper
How do capacitors store charge?
They build up a surplus of electrons on one plate and a deficit on the other
When are there equal amounts of electrons on both plates of the capacitor?
When the capacitor is uncharged
How is a capacitor charged?
When connected to a battery, some of the electrons are removed from one plate and forced onto another, charging the capacitor
What are the two rules for a capacitor?
- Can only be charged by a DC supply
- Cannot be charged to a higher voltage than the power supply
Why won’t an AC supply charge a capacitor?
The electrons vibrate in place; capacitors need electrons to be removed from one plate and transferred to another plate
What type of energy do capacitors store?
Electrical potential energy (due to electrons being pushed together)
What type of energy do batteries store?
Chemical energy
Which stores more charge, a battery or a capacitor?
- Battery
- Batteries can store large amounts of charge whereas capacitors can only store very small amounts of charge
How fast do capacitors release charge? What does this mean for current?
Charge can be released very quickly as a high current
How fast do batteries release charge? What does this mean for current?
Charge is released very slowly, resulting in low currents
State two applications of capacitors
- Power supply for a camera flash
- Back up power supply
State an application of a battery
Power supply for mobile phones
What is capacitance?
The amount of charge stored per unit potential difference
