There are two basic types of electricity: alternating current (AC) and direct current (DC). AC switches directions dozens of times every second, going from negative to positive and back again. DC, by contrast, always flows in the same direction. Power plants produce alternating current or AC electricity. This electricity is sent through the power grid into houses, businesses and other buildings. Batteries, solar panels and certain other power sources use DC electricity. Home appliances are designed to use AC, since AC flows into the home. A DC to AC power converter lets you use a DC source to power one of these appliances.

Early DC to AC converters used a mechanical switch that would flip back and forth very quickly. This would generate pulses of positive and negative current. Modern AC converters use two or more electric switches called transistors. A computer first sends signals to transistors controlling the positive voltage, causing them to make a positive pulse. It then sends signals to transistors controlling the negative voltage, making a negative pulse. AC power flows as a smooth, continuously alternating wave called a sine wave. Most converters, however, do not create an actual sine wave, but a squared-off approximation of it made out of individual electric pulses.

In the United States, electricity flows through the power lines at 120 volts and, in much of the rest of the world it is as high as 240 volts. DC is usually somewhere between 12 and 30 volts, depending on the source - far too low voltage to power appliance designed to run from outlets. To increase the voltage, a DC to AC converter uses a component called a step-up transformer. In a transformer, AC electricity flows through a coil of wire. This creates a moving magnetic field, which produces an electric current in a nearby coil of wire. In a step-up transformer, the second coiled wire has more turns than the first, causing it to produce higher voltage. The electricity from the second coil can then be used to power appliances.

Many electronic devices, from computers to TVs to cell phone chargers, require various DC (direct current) voltages to supply power to circuitry. For those appliances and devices that get their power by plugging them into an electrical wall outlet, a circuit must be designed to convert the 120 volt AC power to a desired DC voltage.

Alternating current, as is found in your home's electric outlets, changes polarity 60 times a second, referred to as "60 Hertz," or "60 cycles". The voltage increases from zero to its maximum positive voltage and then swings below zero to its maximum negative voltage, in a smooth sine wave transition. In a DC voltage supply, the polarity remains constant; plus (+) and minus (-) polarity points do not change, as with a torch battery.

Questions:

1. AC always flows in the same direction – true or false?
2. How does electricity get into people´s homes?
3. The word “appliances” is used in the text  - what do you understand under this term?
4. AC power flows as a smooth, continuously alternating wave. What name is given to this wave?
5. When AC electricity flows through a coil of wire in a transformer what produces the electric current?
6. In terms of changes in polarity what alternative word is used for cycles?

Answers:

1. False
2. Through the power grid
3. Fridge, freezer, microwave, toaster, kettle, etc. (i.e. any white or brown goods)
4. Sine wave
5. A moving magnetic field
6. Hertz