Amp, Volt, and Watt? (Electricity Principles)

Although we can't necessarily see electricity, we can measure it by its effects. An ampere, or amp, represents the amount of current in a circuit. Voltage is defined scientifically as the circuit's "potential difference," and can be seen as the amount of "pressure" that drives electricity in a circuit. Watts are a measure of the use of electrical power, and one watt is equal to one volt multiplied by one amp.

In this case it is helpful to use an analogy to help us understand how each of these terms relate to each other. One commonly used analogy is that of the garden hose. The water pressure in the hose is like the voltage, and the amp value is like the volume of water flowing through the hose. The wattage, then, is the total amount of water that comes out of the hose, per unit of time.

If we replace the hose in the above analogy with an electrical wire, it is simple to see how they relate. In an electrical circuit, the voltage may be 220, as it is in most electrical outlets in all the world except the United States and other few countries. Most appliances are meant to run on this voltage, although each operates at different amp levels, and therefore at a different wattage.

An appliance which uses a large amount of current, such as an electric stove, may be on a separate circuit with a higher voltage. There must be more pressure -- or voltage -- to supply the needed amps to the appliance, because it has a higher wattage. In other words, it uses up more current, or amps, per unit of time, than another appliance. Without the higher voltage, it wouldn't run, because it would be "starved" for the amps it needed to be able to operate.

Another electrical term that helps tie together the other three is the ohm, which is a unit of electrical resistance. Going back to the garden hose analogy, if the hose has a larger diameter, more water will be able to flow through. A circuit with a high resistance value, expressed in ohms, is able to carry fewer amps than one with lower resistance, regardless of the voltage. If a high voltage encounters high resistance, the amount of possible amps in the circuit will be very low -- not much water will get through a narrow hose, no matter how high the pressure is.

Electrical consumption is measured in watts, or watt-hours, and this is the basis on which a power company bills a customer for electrical usage. For convenience, power companies measure consumption in a unit called a kilowatt-hour, which is the equivalent of using 1000 watts of power for one hour. The average household uses hundreds of kilowatt-hours per month.

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