An electrical current is measured by the rate electrons pass a given point in an electric circuit, a higher number of electrons mean a higher level of current. An electrical current "flows" because electrons in a high voltage area are attracted to lower voltage areas and can be controlled to travel along wires. This is known as an electric circuit.
The flow of electrical charge from one point to another is known as the electrical current. Electrical current is measured at the rate it passes through a conductor (a wire, for example). For an electrical current to flow there must be voltage. Voltage is the amount of electrical charge an object holds and is measured in volts. Voltage flows from object to another when two objects connected via a conductor hold differing electrical charges. For example, imagine a piece of metal charged at 10 volts, if it is connected via a conductor to a piece of metal with a charge of 0 volts, an electrical current will be created between the two pieces of metal. This current will continue until the charges of each piece of metal are the same.
A basic circuit works when a difference in voltage is permanently created between two objects. A battery's positive (+) end removes charge from one object while the negative (-) end adds it. Imagine our two pieces of metal again, at one end joined by conductive wire and joined by battery at the other. The battery's positive terminal removes charge causing the negative end to replace the charge. A current is created between the two pieces of metal as the process continues.
Alternating Current (AC)
Alternating current is a type of current in which the direction is constantly reversed or alternated. AC current is the standard in American electricity supplies, alternating 60 times a second. In an AC supply, one wire is negative and the other is either positive or neutral (the earth wire). The two wires take turns, swapping 60 times a second, to provide electricity to an appliance. Imagine an electricity source in a basic circuit connected to a light bulb. In an AC circuit, the electricity source constantly switches its positive and negative ends to send the current traveling in different directions.
Direct Current (DC)
An DC circuit works in the same way as an AC circuit, except that the current always flows in the same direction. DC is used for long distance transmission of electricity because less energy is lost along the way. Appliances that convert electricity in to other types of energy, light bulbs and electric heaters for example, will in theory work fine with an AC or DC current. However, most modern electrical appliances require DC current and are fitted with transformers that convert the AC current from the plug into DC for the appliance to consume.
AC and DC Fact
Bitterly rivaled electricity pioneers Thomas Edison and Nikola Tesla competed over whether AC or DC was the best form of electrical circuit. Edison was a champion of direct current, and Tesla alternating current. The rivalry escalated to the point where Edison electrocuted animals to try and prove the Tesla's current was too dangerous, he began with cats and dogs but eventually electrocuted an elephant named Topsy.