Characteristics of An Alternating Waveform

An alternating current or voltage is the flow of electric charge with periodical reversal in direction. AC voltage or current has a waveform, which represent the frequency of the source. The magnitude of an AC voltage or current, changes with time. The alternating sine current or voltage waveform is a graphical representation of an alternating current or voltage. It can be plotted on a graph with a vertical and horizontal axis. The amplitude of the waveform such as the current or voltage is indicated on the vertical axis measured in volts and the time is indicated on the horizontal or x-axis and it is measured in either seconds or in degrees. An alternating current cycle consists of 360 degrees. As the AC continually changes direction between positive and negative, it plots a waveform represented by a curved line that shifts constantly from positive to negative and then from negative to positive, crossing zero in between.

Photo credit: nothingnerdy.wikispaces.com

Peak Value of an AC

The peak value of an alternating voltage or alternating current is the highest value reached during a cycle. It is the value or amplitude of an AC voltage, which constantly fluctuates. From an initial zero, the amplitude of the AC rises to a high value or a positive peak, which is called the peak value. It then falls back to zero. After reaching zero, the direction of the current changes and the voltage reaches a negative peak value, or a negative peak. The maximum positive peak value occurs at 90 degrees and the maximum negative peak value occurs at 270 degrees. The peak values are the maximum amplitude levels that a waveform will achieve in its travel.

Photo credit: kpsec.freeuk.com/acdc.htm

Instantaneous Voltage of an AC

An instantaneous voltage is the value of the AC voltage at a particular instant. It is also called as the average voltage. The voltages that can be measured at different points of the cycles of the sine waveform are the instantaneous voltages for that sine wave. It is practically impossible to measure the instantaneous voltages. One of the ways of denoting the instantaneous voltage is by taking the average voltage. The average voltage can be measured by multiplying the peak voltage by a constant, which is around 0.367.

Photo credit: macao.communications.museum

Root Mean Square Voltage of an AC

RMS voltage may also be called the effective voltage and it is the voltage read by a voltmeter. A given RMS voltage provides the same amount of power as the same value of DC voltage. RMS voltage is the AC voltage in terms of how much DC voltage it would take to have the same effect in a circuit. During most of the cycle the AC has a value less than the value at its peak than a constant DC voltage. So AC voltage will not be able to produce as much heat in a heating element than a constant DC voltage. The power of the AC voltage is proportional to either E squared "E2" or I squared "I2".

P = E2/R

or

P =  I2R

Photo credit: electronicsarea.com

If all the instantaneous values of a half cycle of a sine wave current or voltage are squared, then the average or mean of all the squared values is found. The square root of this mean value will be 0.707 of the peak value. The RMS value or root mean square value is 70.7 percent of the peak value. The root mean square value represents how effective a sinusoidal AC will be in comparison with its peak value. For determining a peak value of AC that will be effective as a given DC, it is necessary to multiply the effective value given by the reciprocal of 0.707. Reciprocal of 0.707 is

1/0.707 = 1.414

A voltage of 230 volts AC indicates the RMS value and it dissipates the same amount of heat as 230 V DC when applied to the same heater elements. For a domestic supply the effective voltage is 230 volt AC and the peak voltage is 325 V.

The average value of a full cycle of a sine waveform is zero, and it is 0.367 of the maximum voltage or current for a half cycle of the sine wave.

Phase of an AC

Phase denotes the position in angles of the varying voltage from a given instant. When identical amplitude variations of wave forms occur simultaneously they are said to be in phase. When identical amplitude variations do not occur simultaneously they are said to be out of phase.