A DC circuit consists of a source (e.g. battery or power supply) and a load (e.g. light bulb or electronic instrument). The electrons move from the negative terminal of the source, towards the load and then return to the positive terminal of the source, i.e. the electrons flow in only one direction . This movement of electrons will continue as long as there is a closed circuit.
In contrast, the source in the AC circuit is constantly changing. The voltage of the source builds up and electrons flow through the circuit in the same way as for the DC circuit. However, as the voltage of the source decreases, reverse polarity occurs and the direction of the electron flow is reversed. Depending on the load, it may be required for current to flow in one direction only. In this case, the AC current will need to be converted into DC current.
The basic properties of alternating current are : Frequency (represented by ‘f’, expressed in Hz and measured in cycles/sec), Period (reciprocal of frequency and measures the time taken to complete a waveform. In the UK, the frequency of the AC power system is 50Hz, therefore the period will be 1/50 = 0.02 sec/cycle), Wavelength (measures distance per cycle and is expressed as . Typically, = c/f, where ‘c’ is the speed of light which is 3x108 meters/second) and Amplitude (value of a sine wave at its peak, expresses how positive or negative the voltage is).
The most important properties of AC power are frequency and amplitude. The frequency and power of the voltage lines determines the design of the electrically powered equipment. Period is sometimes considered, and wavelength becomes more important when working with signals at higher frequencies.
References
Bigelow, K. (2015). www.play-hookey.com. Retrieved from Alternating Current Topics: http://www.play-hookey.com/ac_theory/
