AC electricity

The letters “DC” stand for direct current, the type of electricity produced by batteries. DC electricity was investigated by Italian physicists Luigi Galvani and Alessandro Volta around 1800. All of the circuits discussed so far in this chapter, and which you have built in the lab, have been DC circuits. Thomas Edison created the first electric light bulbs to operate on DC current. Read the text aloud
The electricity in your home is alternating current or AC. With AC electricity the polarity, meaning which wire is positive, changes many times per second. Imagine a battery on a rotating wheel with contacts that alternately connected the wires to opposite poles of the battery. The voltage on one wire would alternate back and forth between positive and negative. Read the text aloud A rotating battery produces an alternating current.
If the voltage alternates, so does the current. When the voltage is positive the current in the circuit is clockwise (see the graph). When the voltage is negative the current flows in the opposite direction. In actual AC circuits, the hot wire carries an alternating voltage that alternates from positive to negative. The other wire is held at a constant zero volts. Read the text aloud
AC electricity is used for high-power applications because it is easier to generate and transmit over long distances. In Chapter 19 you will see that electric generators naturally make AC power. All the power lines you see overhead carry AC current. The plugs in the walls of your apartment or house or classroom also carry AC. Read the text aloud Show The Current Wars of the 1880’s
AC electricity is used in homes. The 120 volt AC (VAC) electricity used in homes and businesses alternates between peak values of +170 V and −170 V. This kind of electricity is called 120 VAC because +120 V is the average positive voltage and −120 V is the average negative voltage. AC electricity is usually identified by the average voltage, not the peak voltage. Read the text aloud
The frequency of AC electricity is an important characteristic. In the USA, AC power alternates at a frequency of 60 Hz. This means the voltage on the same wire switches back and forth between positive and negative 60 times each second. European and some South American countries operate their power grids at 50 Hz and 220 V. The higher voltage and different frequency mean electrical devices designed for 120 V, 60 Hz power do not work, or are destroyed, by lower frequency, higher voltage European power. Read the text aloud

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