|Zitzewitz, Paul & Robert Neff. Physics. New York: Glencoe, 1995: 481.||"Suppose, that a 240 W television is plugged into a 120 V outlet."||120 V|
|"Electricity." Grolier Multimedia Encyclopedia. CD-ROM. Acbel Technologies, 1996.||"For instance, voltages measured in an electrocardiogram peak at 5 millivolts; many are familiar with the 115-volt potential of a house."||115 V|
|Trefil, James. Sharks Have No Bones - 1001 Things Everyone Should Know About Science.Simon & Schuster. 1992: 123.||"The 115-volt current that comes out of your household wiring is normally stepped down by…."||115 V|
|"Electric Power." Worldbook Encyclopedia. Chicago: Field Enterprises, 1970: 141.||"But homes, stores, and farms need current at still lower voltages, usually from 120 to 240 volts."||120–240 V|
|"Electricity." American Heritage Encyclopedia. 1994: 135.||"Electrical appliances power tools, and other home equipment operating on 120 volt or 240 volt circuits."||120 V
Electromotive force, also known as EMF, is that which tends to cause the flow of electricity. It is the electric energy per unit charge derived from a battery or a generator. Usually it is called the electric potential difference and is measured in volts. EMF is related to electric force, but is not actually a force. It is the energy required to carry a unit positive charge once around a closed circuit. It is the product of electric intensity or field strength (measured as force per unit charge) and the distance traveled around the closed unit.
Voltage is usually thought of as the "push"that moves or tends to move a current through a conductor. The unit of voltage is the volt, named after Alessandro Volta, the Italian scientist who built the first battery. The more technical meaning of voltage is the unit of electromotive force that will drive a current of one ampere through a resistance of one ohm. One volt is practically the electromotive force of a simple voltaic cell.
The reason why things have different voltages is because not everything needs the same EMF to drive a current through it. Big industrial plants usually receive electric power at about 13,800 volts or higher, where a flashlight battery has approximately 1.5 volts.
Different sources may give you different numbers when describing the voltage of household electrical outlets (or anything for that matter). However, the numbers that are determined are usually pretty close. The most common voltage of household electrical outlets I arrived at was 120 volts, but I also came across 115 volts (twice). These two numbers are near each other and that is how it should be. I also came to the conclusion that 240 volts was the voltage for heavy duty household receptacles.
Samara Martinez -- 1999