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Name:___________________________________ Date:______________ Hour: 1 2 3 4 5 6 Chapter 34 Summary Electric charge comes from the electric forces between the positively charged protons and negatively charged electrons. The flow of charge is called electric current and is measured in amperes (amps). The symbol is I and the abbreviation for the units is A. A difference in electric pressure at both ends of a conductor causes charges to flow. The source of this constant potential difference is called a voltage source and is measured in volts, abbreviated v. Since protons are trapped in the nucleus, the electrons are the moving charges. When charges are not flowing, the net charge in the wire is zero. When charges are flowing the net charge in the wire is zero because for every one charge that enters one side, another charge leaves the other side and the total number of protons and neutrons doesn’t change. DTE supplies power to the outlets in your wall with a potential difference of 120 volts and an alternating frequency of 60 hertz. Resistance is the opposition to current flow. It’s symbol is R and the units are ohms, abbreviated Ω. Resistance basically depends on 3 things. Thicker, shorter, cooler wires have less resistance which will allow more current to flow. When getting shocked, high voltage is painful and can be deadly, but current is much more dangerous. As little as 0.07 A can kill you. There are 2 types of flow for current: direct current (DC) and alternating current (AC). DC flows in one direction, is more portable to generate, but has a finite amount of energy. Current switches direction for AC, is easier to continually produce because we don’t have to supply any electrons, just move them, but is harder to produce in a portable package. Electric power is calculated by multiplying current and voltage. The symbol is P and the units are watts (W). Because our house uses so much power, we use bigger units for power: kilowatts (kW). To calculate the energy we use, multiply power and time (in hours). We are charged for energy in kilowatt hours (kWh).