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.

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.