(EAM) Electric Currents and Circuits Lesson

Electric Currents and Circuits

The flicker of numbers on a handheld calculator, nerve impulses carrying signals of vision to the brain, an ultrasound device sending a signal to a computer screen, the brain sending a message for a baby to twitch its toes, an electric train pulling its load over a mountain pass, a hydroelectric plant sending energy to metropolitan and rural users—these and many other examples of electricity involve electric current, the movement of charge. Humankind has indeed harnessed electricity, the basis of technology, to improve our quality of life. Whereas the previous lesson concentrated on static electricity (the build-up of electric charge), this lesson will be devoted to electric current and circuits.

Current

Electric current is defined to be the rate at which charge flows. A large current, such as that used to start a truck engine, moves a large amount of charge in a small time, whereas a small current, such as that used to operate a hand-held calculator, moves a small amount of charge over a long period of time.   This current of electrons can be in one direction or direct current (DC) electricity, or it can alternate back and forth as alternating current (AC) electricity.

Free electrons will flow through a conducting material such as a metal wire when there is an electrical field applied to the wire in the form of a potential difference or voltage at the ends of the wire. The electrons will then flow toward the area that contains a positive electrical charge.

Scientists use the symbol I to show current and measured current in amperes (A). An ammeter is an instrument used to measure the rate of flow of electric current in a circuit. Later in this lesson, we will look at the relationship between current, resistance, and voltage, however first we must look at the two types of current: direct current (DC) and alternating current (AC).

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