the capacitance of an object is the amount of charge it is able to store per unit of potential difference across it.
C in farads, f Q in coulombs, C V in volts, V
Capacitor: an electrical component that can store charge, made up of two conducting plates seperated by a dielectric.
- when a capacitor is connected to D.C., charge builds up on its plates.
- one plate becomes +ve and one becomes -ve
- plates are seperated by electrical insulation so no charge moves between them.
-this means a potential difference builds up between the plates.
capacitance part 2
uses of capacitors:
- camera flash, battery chargs the capacitor then all the charge is instantly used as the flash
-'ultracapacitors' are really big capacitors that can be used in back-up power supplies to provide reliable power for short periods of time.
-to smooth out variations in D.C. voltage supplies - a capacitor absorbs the peaks and fills in the peaks.
Charging and discharging
Q = Qo e -t/RC
Q = charge of capacitor at the time
Qo = charge of capacitor when fully charged
e = constant on calculator and formula sheet
-t = time since discharging began
-R = resistance of fixed resistor
-C = capacitance of capacitor