(EAM) Currents Lesson

Currents

Direct Current 

Direct current or DC electricity is the continuous movement of electrons from an area of negative (−) charges to an area of positive (+) charges through a conducting material such as a metal wire. Whereas static electricity sparks consist of the sudden movement of electrons from a negative to a positive surface, DC electricity is the continuous movement of electrons through a wire.

A DC circuit is necessary to allow the current or steam of electrons to flow. Such a circuit consists of a source of electrical energy (such as a battery) and a conducting wire running from the positive end of the source to the negative terminal. DC electricity in a circuit consists of voltage, current, and resistance. The flow of DC electricity is similar to the flow of water through a hose.

Alternating Current

If the terminals constantly switch their polarity from (+) to (−) and back again, the direction of the electrons alternates back and forth and is called alternating current or AC electricity.  Alternating current (AC) is the type of electricity commonly used in homes and businesses throughout the world. While direct current (DC) electricity flows in one direction through a wire, AC electricity alternates its direction in a back-and-forth motion. The direction alternates between 50 and 60 times per second, depending on the electrical system of the country.

AC electricity is created by an AC electric generator, which determines the frequency. What is special about AC electricity is that the voltage can be readily changed, thus making it more suitable for long-distance transmission than DC electricity. Many electrical devices—like light bulbs—only require that the electrons move. They don't care if the electrons flow through the wire or simply move back and forth. Thus a light bulb can be used with either AC or DC electricity.

Uses and Advantages of AC and DC

Direct current (DC) is the flow of electric charge in only one direction. DC is used in many devices that do not require high voltages for their operation, such that batteries are used for power. Alternating current (AC) is the flow of electric charge that periodically reverses direction. AC can be used at higher voltages. It has the advantage of being able to have its voltage easily changed to a higher or lower level. AC is required for many electronic devices.

Most large power-distribution systems are AC. Moreover, the power is transmitted at much higher voltages than the 120-V AC (240 V in most parts of the world) we use in homes and on the job. Economies of scale make it cheaper to build a few very large electric power-generation plants than to build numerous small ones. This necessitates sending power long distances, and it is obviously important that energy losses en route be minimized. High voltages can be transmitted with much smaller power losses than low voltages, as we shall see. For safety reasons, the voltage at the user is reduced to familiar values. The crucial factor is that it is much easier to increase and decrease AC voltages than DC, so AC is used in most large power distribution systems.

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