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Alternating Current and Direct Current

Updated on August 8, 2012
Alternating Current
Alternating Current
Square wave - Alternating current
Square wave - Alternating current

Definition of Alternating Current and Direct Current

Electricity is defined by movement of charges, electrons, inside a conductor. Hence, the term current is used to describe the flow of electricity. There are two ways electrical power flows through a conductor and that is what we call direct current and alternating current.

Direct current is a type of flow of electricity wherein the direction of flow is always in one direction only. Direct current is ideally constant – meaning, neither current nor voltage changes. However, due to the imperfections of rectification processes(the process of converting alternating current to direct current), sometimes a pulsating Direct current signal is obtained. For more details on rectification processes, read this article about rectifiers.

Direct current is usually obtained from batteries, chargers, solar cells, and DC Generators. DC is usually used for powering electronic devices like laptops and cellular phones.

Alternating current is usually described, but not limited to, Sinusoidal waveforms. Alternating current is a type of current wherein the direction of the flow of current is periodically reversed. An alternating current has a positive cycle and a negative cycle where in each cycle, the direction and magnitude of the current is described by its position on the y axis of an x-y coordinate. Alternating current can also be triangular wave-forms, square waves and saw-tooth waves. In small signals, alternating current can be shifted along the y-axis meaning, its maximum peak and minimum peak values can be adjusted. And the two does not necessarily need to be equal for a source to become an alternating current. For more information on how Alternating current is “shifted along the y-axis” read this article about diode clamper circuits.

Alternating current is usually obtained from Generation Power Plants and is usually produced in a polyphase system. It can also come from AC generators. AC usually used for transmitting power and is what comes out of our power outlets.

Sinusoidal waveforms
Sinusoidal waveforms

Advantages and Disadvantages of Alternating Current (AC) and Direct Current (DC)

In the late 1800’s, Thomas Edison introduced Direct current as a way of commercially distributing electricity, however because of the disadvantages of the Direct current Alternating current was then used. Direct current introduces a lot of losses when used to distribute electricity. It is easier to raise the voltage or current of an alternating current. Since losses are minimal at higher voltages and lower currents, Alternating current is a favored way to distribute electrical power.

Direct current also has some advantages in distribution. Direct current is more efficient when transmitting electricity at very long distances since a direct current will not introduce losses due to reactance which is present in AC systems. Direct current used in transmission, like AC, is converted to high voltage-low current to minimize losses. There are a few distribution systems that use DC to distribute electricity.

Direct current is favored in small electronics because power sources like batteries or solar cells produce electricity as Direct current. However, small electronics do not purely use DC in its system. AC is likely to be present since an alternating current has the ability to transmit information by varying its amplitude of frequency.

Alternating Current and Direct current has its pros and cons and the reason why we don’t just use one type for all our electricity consuming appliances and gadgets is because of efficiency. Appliances are in AC since outlets are in AC. And our gadgets are in DC since batteries are in DC. We may be able to live with only one form of electricity but that would be very expensive.


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    • profile image

      Cristian 2 years ago

      Hi Hilma,You are dead on with your information. I went for mothns not know what was going on because my doctor told me my numbness would go away. I suffered for 6 mothns. I had nerve transmission tests, an MRI, and got no relief until I tried physical therapy. I was diagnosed with thoracic outlet syndrome affecting the ulnar nerve. But even after mothns of therapy I still had intermittent numbness and pain. Your videos and website info helped me figure out I also had pectoralis minor syndrome. Thankfully I am much better now. Thank you for the thought and care you put into your videos and website. You have helped me a lot! Take care.

    • leakeem profile image

      leakeem 5 years ago from Earth

      I think it's just pulses (what controls the muscles). As for electric eels, I'd go with DC because the only way you can create AC directly is with a rotating machine. Unless of course eels have inverter like circuits in them which would be cooool.

      About DC for long distances. DC is more effective for long distances because it eliminates reactance within the power lines since the lines will have some capacitance. Generator systems generate power in AC and the cost of transforming that power to DC (since, it's large scale) is expensive. However, since losses due to reactance in long range transmission wires are larger, DC transmission is better for very, very long range transmission.

      For smaller grids, DC is impractical because of the cost of conversion from AC to DC.

    • Window Pain profile image

      Window Pain 5 years ago

      I've always heard about living things having an electrical current. Is it DC or something else altogether? I have no idea.

      I have to say you lost me on DC being able to transmit a long distance, but not in normal grids.

      (You have no idea, the strength it takes, not to go pun-crazy in this reply! Maybe I'm growing up.)