Electric Energy and Current Chapter 18 Electrical Potential Energy- the potential energy between charges at a distance, or between a charge and an electric field.  PE = -qEd As a charge moves, it gains KE, and loses PE.

Potential Difference- the work that must be done to move a charge. Many different names- Potential, Potential Difference, Voltage, Emf. Symbol is V, units are V = J/C.  V =  PE/q  V = -Ed V = kq/r In order to have energy stored, you must keep the terminals of the battery at different potential (ie different levels of charge)

Capacitance- the abilityof a conductor to store energy in the form of electrically separated charges. Symbol is C, unit is the Farad, F. C = Q/V 1 Farad = 1 Coulomb/Volt Parallel plate Capacitor (most common) C =  0 A/d A=area, d= distance between plates   = 8.85 E-12

Capacitance can be changed by putting something between the plates of a capacitor. We call this a dielectric. A dielectric is an insulating material- examples are glass, rubber, wood, waxed paper, etc. Molecules in dielectric become polarized, line up with electric field. This allows for a weaker electric field between the plates, so the plates can store more charge. Capacitance increases with a dielectric.

An example of a capacitor is the flash in a camera. Energy stored in a charged capacitor PE = ½ QV Since Q = CV, PE = ½ CV 2 Usually capacitance and charge are small units pF = F nC = C  C = C