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Difference Between Direct Current and Alternating Current

Direct Current vs Alternating Current

In order to power all our devices and appliances, we need power. This is generated by power plants and are delivered to us in a variety of ways. Direct current and alternating current are the two ways of transferring power from one point to another with the use of conductors. The main difference between the two is in how the current flows. Direct current, commonly abbreviated as DC, flows uniformly in one direction while alternating current, also commonly abbreviated as AC, changes direction at a given rate or frequency. The main consequence of this is the polarity of the voltage. With the DC, the polarity remains constant while with AC, it constantly switches between positive and negative. With AC, the voltage is expected to constantly reverse and polarity is not really important. That’s why you can plug-in your appliances to a wall socket in either orientation and not have any problem. Because DC keeps a constant polarity, it is important that you pay attention to how you connect your device as reversing the polarity can damage your device. A good example of this are battery operated devices. As you can only get DC from batteries, battery operated devices clearly indicate how they should be placed. The primary reason for the proliferation of AC is the relative ease and efficiency in increasing and decreasing the voltage. This is achieved with the use of transformers and the amount increased or decreased is determined by the amount of windings. Although it is also possible with DC, it is a lot more complex or inefficient to do. This is also the reason why AC is used in the electrical mains. While it is easier to generate lower voltages, high voltages incur lower losses during transmission. Before transmission, the AC voltage is stepped up to hundreds of kilovolts and then lowered back down to 110 or 220 volts once it reaches its destination. As already stated above, AC has two well established standard voltages that are in use around the world; 220V and 110V. With DC, voltages vary widely among different devices. Typical values include 1.5V, 3.7V, 6V, 9V,12V, 24V, and so on.


1. DC has a constant polarity while AC has a changing polarity

2. DC is particular about polarity while AC is not

3. You only get DC from batteries and not AC

4. AC is easier and more efficient to step up or down than DC

5. DC has a much wider variety of standard voltages than AC

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1 Comment

  1. AC voltage can be changed to DC by using diodes to rectify it. The diodes allow AC to flow in only one direction. This is done in AC welding machines that can also produce DC.

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