- Created by: NoLongerHuman
- Created on: 21-01-19 10:12
21.1 - Capacitors
- Designed to store charge, similar to a cell
- Two metal plates seperated by a insulator, i.e. ceramic, plastic
-When connected to a battery/cell, electrons are moved from the left plate and deposited on the right plate.
- Plate charges become +Q and -Q
- Full charge is achieved when capacitor p.d.=cell e.m.f.
- Q on a plate is directly proportional to p.d. across it, so Q=VC (where C is capacitance)
- Capacitance (measured in Farads, F) is:- The charge stored per unit p.d.
- 1 farad = 1 coulomb per unit volt
21.2 - Capacitors in circuits
- Parallel:- p.d. is constant - Qtotal = sum of individual charges (Q1+Q2+...) - Ctotal = sum of capacitances (C1+C2+...)
- Series:- Q is constant - Vtotal = sum of individual voltages (V1+V2+...) - 1/Ctotal = sum of 1/capacitances (1/C1+1/C2+...)
21.3 Energy in capacitors
- During charging, work is done to move the elctrons away from the +ve plate and towards the -ve plate
- Work done = area under a p.d.-charge graph (W=1/2QV)
- Using Q=VC, we also get W=(Q^2)/2C and W=1/2(V^2)C