Why is ac used instead of dc

Useful tool: Units Conversion. This movement is made easier in an electric conductor, such as a metal wire. The same thing happens with a DC generator, where the motion of coiled wire through a magnetic field pushes electrons out of one terminal and attracts electrons to the other terminal. With an AC generator, a slightly different configuration alternates the push and pull of each generator terminal. Thus the electricity in the wire moves in one direction for a short while and then reverses its direction when the generator armature is in a different position.

This illustration gives an idea of how the electrons move through a wire in AC electricity. Of course, both ends of the wire extend to the AC generator or source of power. AC electricity alternates back-and-forth in direction 50 or 60 times per second, according to the electric system in the country. This is called the frequency and is designated as either 50 Hertz 50Hz or 60 Hertz 60Hz.

Many electric 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.

As more devices begin to use lower voltages, there is less need for power conversion. It ultimately holds an advantage over AC-powered LED lights, all of which flicker, meaning a constant fluctuation of light output from on to off. However, the world continues to opt for the simplest method of delivering power. AC voltage generates efficiently and has been continuously tested by time.

As of now, not enough devices are attuned to working with DC voltage for it to become mainstream practice, and economic and practical results of switching fully to DC power are unpredictable. While DC voltage is gradually disproving its inefficiency in supplying power across wider distances, AC voltage still provides the easiest, most reliable electricity that allows people to go through their days easily. You must Sign in or Register to post a comment.

As opposed to direct current, the direction and amperage of alternating current changes many times a second. An alternating current will flip the direction of charge flow 60 times a second in North America 60 Hz and 50 times a second in Europe 50 Hz. This is usually caused by a sinusoidally varying current and voltage that reverses directions, creating a periodic back and forth motion for the current see Figure 1.

Despite this current flowing back and forth many times a second, the energy still essentially flows continuously from the power plant to the electronic devices. A major advantage of alternating current is that its voltage can be modified relatively easily using a transformer , which allows power to be transmitted at very high voltages before being taken down to safer voltages for commercial and residential use.

As seen in the first equation, the power lost through transmission is proportional to the square of the current through the wire. Therefore, it is preferable to minimize the current through the wire so that the energy loss is reduced. Of course, minimizing the resistance would reduce the energy lost as well, but the current has a much larger impact on the amount of energy lost due to its value being squared.

The second equation shows that if voltage is increased, the current is decreased equivalently to transmit the same power. AC can be produced using a device called an alternator. This device is a special type of electrical generator designed to produce alternating current. A loop of wire is spun inside of a magnetic field, which induces a current along the wire. The rotation of the wire can come from any number of means: a wind turbine, a steam turbine, flowing water, and so on. Because the wire spins and enters a different magnetic polarity periodically, the voltage and current alternates on the wire.

Here is a short animation showing this principle:. Generating AC can be compared to our previous water analogy :. To generate AC in a set of water pipes, we connect a mechanical crank to a piston that moves water in the pipes back and forth our "alternating" current. Notice that the pinched section of pipe still provides resistance to the flow of water regardless of the direction of flow. AC can come in a number of forms, as long as the voltage and current are alternating.

If we hook up an oscilloscope to a circuit with AC and plot its voltage over time, we might see a number of different waveforms. The most common type of AC is the sine wave. The AC in most homes and offices have an oscillating voltage that produces a sine wave.

Triangle waves are found in sound synthesis and are useful for testing linear electronics like amplifiers. We often want to describe an AC waveform in mathematical terms. For this example, we will use the common sine wave. There are three parts to a sine wave: amplitude, frequency, and phase. V t is our voltage as a function of time, which means that our voltage changes as time changes. The equation to the right of the equals sign describes how the voltage changes over time.

V P is the amplitude. The sin function indicates that our voltage will be in the form of a periodic sine wave, which is a smooth oscillation around 0V. This is given in the form of hertz or units per second. The frequency tells how many times a particular wave form in this case, one cycle of our sine wave - a rise and a fall occurs within one second. As time varies, our waveform varies. Phase is a measure of how shifted the waveform is with respect to time. It is often given as a number between 0 and and measured in degrees.

We can turn to our trusty outlet for a good example of how an AC waveform works. In the United States, the power provided to our homes is AC with about V zero-to-peak amplitude and 60Hz frequency. We can plug these numbers into our formula to get the equation remember that we are assuming our phase is 0 :.

We can use our handy graphing calculator to graph this equation. If no graphing calculator is available we can use a free online graphing program like Desmos Note that you might have to use 'y' instead of 'v' in the equation to see the graph.

Notice that, as we predicted, the voltage rise up to V and down to V periodically. Additionally, 60 cycles of the sine wave occurs every second.