1. Electric Energy and Current Chapter 17 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.

2.  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. DV = DPE/q DV = -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)

3.  The gap between electrodes in a spark plug is.060 cm. Producing an electric spark in a gasoline-air engine requires an electric field of 3x10 6 V/m. What minimum potential difference must be supplied?

4.  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 = e 0 A/d A=area, d= distance between plates e 0 = 8.85 E-12

5.  A capacitor connected to a 12V battery source hold 36 μ C of charge on each plate. What is the capacitance?

6.  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.

7.  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 = 10 -12 F  nC = 10 -9 C  C = 10 -6 C

8.  Find the electrical potential energy stored in the capacitor in the previous problem