Please enable JavaScript.
Coggle requires JavaScript to display documents.
Module 6 - Chapter 21 - Capacitance I - Coggle Diagram
Module 6 - Chapter 21 - Capacitance I
Capacitors
Electrical components where charge is separated
Consists of two metallic plates separated by an insulator (dielectric) which could be air, paper or ceramic
Storing charge
When connected to a cell, electrons flow from the cell for a very short time
Electrons can't travel through the plates due to the insulator
Electrons are removed from plate A, it becomes defiicent in electrons, so has a positive charge
Electrons are deposited on plate B, which gains electrons and becomes negatively charge
Current is the circuit must be the same, and charge must be conserved, so two plates have equal and opposite charge
There is a pd across the plates, and the current falls to zero when the pd across teh plates equals the emf (Capacitor is fully charged)
Capacitance
Capacitors are marked with their capactiance value ( amount of charge they can store for a given pd)
Capactiance - charge stored per unit pd across it
Measured in Farads (F)
Greater amount of positive and negative charge stored, the greater the pd across them
Charge is proportional to the pd
Capacitors in circuits
Parallel
Two connected in parallel have a greater capactiance than individually
Pd across each capacitor is the same
Electrical charge is conserved, total charge is the sum of the individual charges stroed by the capacitors
Total capacitance is the sum of the individual capacitances of the capacitors
Proof
Total charge is the sum of the individual charges
Sub Q = VC into the equation
V is the same across the capacitors, so
Series
Total is less than their individual capacitance
All capacitors in series store the same charge, middle two plates between adjacent capacitors have the same charge as electrons are transferred between them
Overall charge is 0, but magnitude on each plate is Q and charge stroed by each capacitor is the same
Total capactican is
Proof
Rearrange using Q = VC
Q stored by each capacitor is the same, so Q cancels out
Energy storage
Pushing/ removing electrons
Electron moves towards the negative plate of a capacitor being charged
Electron experiences a repulsive electrostatic force from the electrons on the plate
External work has to be done to push the electron onto the negative plate
Work is done to cause an electron to leave the postitive plate of the capactior
External work is provided by the power supply, energy in the capacitor comes from the energy of the battery
PD/ Charge graphs
Work done to increase charge stored in the capacitor =
Area of thin strip is the work done. The total area under the graph is the total work done on the charges for a charging capacitor
Stored energy
Work done on charges is the same as the energy stored in the capacitor
From the area under the trirangle, we derive
From Q = VC, we get
W is directly proportional to V^2
From V = Q/C, we get
Dielectric insulators
Increases capacitance of device by polarizing in the electric field and effectively increasing the charge stored
Insulator is rarley a vacuum as it doesn't polarize well
