Capacitance and Dielectrics. AP Physics C Montwood High School R. Casao. Definitions. Voltage —potential difference between two points in space (or a circuit). Capacitor —device to store energy as potential energy in an E field.
AP Physics C
Montwood High School
The battery will move charge from one conductor to another until the voltage produced by the charge buildup is equal to the battery voltage.Definition of Capacitance
An electric field E is established between the charged conductors.
A capacitor is a device whose purpose is to store electrical energy which can then be released in a controlled manner during a short period of time.Definition of Capacitance
When the switch is closed, the battery establishes an electric field in the wire that causes electrons to move from the left plate into the wire and into the right plate from the wire. As a result, a separation of charge exists on the plates, which represents an increase in electric potential energy of the system of the circuit. This energy in the system has been transformed from chemical energy in the battery.
For a spherical conductor of radius R and charge +q (the conductor with the –q charge can be considered as a hollow conducting sphere of infinite radius):
The voltage of the sphere isCapacitance of a Lone Spherical Conductor
Use Gauss's Law to calculate the electric field E between the plates of the charged capacitor:Parallel Plate Capacitor
The electric field E is perpendicular to the axis of the cylinders and is confined to the region between the cylinders.Cylindrical Capacitors
Substitute into the capacitance equation:Cylindrical Capacitors
+Q on center conducting cylinder
-Q on outer conducting cylinder
The electric field E between the two spheres is given by:Spherical Capacitors
Substitute into the capacitance equation:Spherical Capacitors