Notes from pages 553-563

• Sources of electrical energy: Voltaic cells - e.g; common dry cells batteries for portable electric devices. Piezo electricity - e.g; phonograph cartridges, barbecue spark starters. Thermoelectricity - e.g; gas appliance pilot light safety system; current keeps gas value open as long as flame is lit. Photo electricity - e.g; satellite and international space station supply, calculator power supply. Electromagnetic induction in generation - e.g; hydro, nuclear, fossil-fuel-powered electric generators.
• Amount if energy transferred depends on two things; the potential difference of the power supply and the nature of the pathway through the loads that are using the electric potential energy.
• The more difficult the path, the more oppostion there is to flow. The measure of this opposition to flow is called resistance. 
• Ohm's law: R = V/I  --> R (resistance in volts/ampere), V (difference in volts), I (resulting current in amperes)
• The resistance of a conductor depends on its length, cross-sectional area, the material it is made of and its temperature.
• The gauge number of a wire indicates its cross-sectional area. A wire that has a small gauge number has a large cross-sectional area. Similarly, a small cross-sectional has a large gauge number. 
• In a series circuit, the loads are connected one after another in a single path, whereas in a parallel circuit, they are side by side. 
• Kirchhoff's current law; the total amount of current into a junction point of a circuit equals the total current that flows out of that same junction.
• Kirchhoff's voltage law; the total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop. 
• In any circuit, there is no net gain or lose of electric charge or energy.
• Superconductivity is the ability of a material to conduct electricity without heat loss due to electrical resistance. The promise of superconductors is transmission lines that carry electricity without energy loss.
• Three-way light bulbs, which have three different light intensity settings, have two filaments of different  resistance connected in parallel. Each filament can be turned on separately, or they can both be turned on at the same time, thus producing three different light intensities.