Ch+16+-+Elec+Energy+and+Capacitance

__**Electrical Energy and Capacitance**__



__**capacitor:**__ An electrical component that has the ability to store electric charge.

__**Application of Capacitors:**__ Many common house hold items use capacitors. Such items include [|electrostatic precipitators] (air cleaner), and [|laser printers].





__**capacitance:**__ (//C//) The ratio of the magnitude of the charge on either conductor of a //capacitor// to the magnitude of the potential difference between the conductors. __**dielectric constant:**__ (Symbol = k ) A material constant that measures the increase in capacitance that it produces when inserted between the plates of a capacitor. where //C//0 is the capacitance without the dielectric. **__dielectrics:__** Insulating materials such as rubber, glass, or waxed paper that have the property of electric //polarization//. __**dielectric strength:**__ The maximum electric field that a dielectric-filled capacitor can support before there is an electric discharge between the plates of the capacitor. __**electric potential difference:**__ The electric potential difference between points //A// and //B//, D //V//, is the change in potential energy (final value minus initial value) of a charge, //q//, moved from //A// to //B//, divided by the charge.

The units of electric potential difference, a scalar quantity, defined as the volt (V). __**electron volt:**__ (ev) The electron volt is defined as the energy that an electron (or proton) gains when accelerated through a potential difference of 1 V. __**Equipotential surface:**__ A surface on which all points are at the same electric potential. __**microfarad:**__ (Symbol = m f) A common unit of capacitance equal to 1 X 10-6 F. __**parallel combination:**__ A description of two or more capacitors connected such that their left sides are commonly connected and their right sides are commonly connected. The equivalent capacitance of the parallel combination of //n// capacitors is given by __**parallel-plate capacitor:**__ A capacitor consisting of two parallel conducting plates. The capacitance of a parallel plate capacitor is: where //A// is the area of one of the plates, //d// is the separation between the plates, and e 0 = 8.85 X 10-12 C2/N-m2 is the //permittivity of free space//. __**picofarad:**__ (Symbol = pf) A common unit of capacitance equal to 1 X 10-12 F. __**polarization:**__ The process that occurs in certain materials where there is a shifting of the positive charge to one side of the molecule. __**series combination:**__ A description of two or more capacitors connected such that the right side of one capacitor is connected to the left side of the next capacitor. The equivalent capacitance of the series combination of //n// capacitors is given by:

The difference in electric potential between two points A and B is where (delta)PE is the change in electrical potential energy experienced by a charge q as it moves between A and B.
 * (delta)V=Vb-Va=(delta)PE/q**

The electrical potential diffrence between two points is A and B in a uniform electric field E is where d is the distance between A and B and E is the strength of the field in this region.
 * Vb - Va = -Ed**

The electric potential due to a point charge q at distance r from the point charge is
 * V = Ke(q/r)**

The electrical potential energy of a pair of point charges seperated by distance r is An easy way to remember this is to remember last year when you learned about gravity. It is the same equation(making reference to **G(m1m2/r)**, so that makes it fairly easy to relate. The only difference is that you are dealing with electric fields and not gravitational fields.
 * PE = Ke (q1q2/r)**

A capacitor consists of two metal plates wirh charges that are equal in magnitude but opposite in sign. The capacitance(C) of any capacitor is
 * C = Q/(delta)V

Permittivity of free Space-** 8.85×10^-12 C^2/Nm^2.

Here is an example of a capacitance problem.

First use the series equation to find the capacitance of the circled capacitors. This is what you should obtain once you complete the first step. From the picture above we use the parallel equation to combined the capacitors. The the last step is to use the series equation to get the final product.