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.

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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.

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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.

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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

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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.

Alternating Current And Its Applications

Alternating current or alternating voltage is the current or voltage that changes its amplitude in a waveform through a conductor or medium as it flows.  It is the flow of electric current or voltage that reverses its direction in each alternation. Alternating current is abbreviated as AC. The flow of  charge reverses its direction in a circuit back and forth creating an alternating current. The magnitude of an alternating current increases from zero to a maximum for a moment and then returns back to zero.

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AC Waveform

The usual waveform of an AC circuit is a sine wave. In other applications different waveforms are used such as the triangular or square waveforms. The direction of an AC alternates between both directions either positive or negative. The AC voltage changes its waveform from zero to positive and then to zero, zero to negative and then to zero. The rate of alternation of the alternating current is cycles per second. The frequency of an AC voltage or AC current is the number of cycles per second. The frequency of an AC is measured in hertz or Hz in short. The cycles of direction change is usually about 50 to 60 cycles per second, that occurs continuously. The time taken by the AC current or voltage to complete once cycle is known as its time period.

F "Frequency in Hertz" = 1 / T "Time in Seconds"

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Sources of AC

Alternating current is produced by alternators, generators, dynamos, oscillators, signal generators, etc.

Uses of AC

Alternating current is the type of electricity used in domestic and business houses. The cycles of direction change is usually dependent upon the type of electrical system of the place. The AC is used in our houses for lighting and heating purposes. The devices that run on AC are lighting devices, electric fans, coolers, air conditioners, electric iron, electric oven, washing machines etc.

Advantages of AC

1. Alternating current or AC can be changed from one voltage to another of the same frequency. The varying current and voltage induces a varying magnetic field in a transformer, which in terms transforms it into another voltage.

2. AC generators and motors are very simpler in design and manufacture than DC generators and motors.

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AC Applications

AC allows the transmission of electricity  through long distances from where it is generated to where it is  consumed. Very high AC voltage in the range of several 1000s of volts  are used for carrying energy from the power house to the substation. From the substation the high voltage is transformed into lower voltage which is supplied for the domestic purposes.

Signal waveform transformation and transmission is possible only through AC. Signals such as audio, radio etc. are carried by alternating currents of those signal frequencies.

AC transformers are used for converting higher voltage AC to lower volt AC and vice versa. It also couples similar voltage AC from one circuit to another for matching and coupling.

AC motors are used in fans, compressors, starter motors, water pumps, electric vehicles, electricity operated flights, etc. for their respective functions.

Alternating current can pass through inductance and capacitance and produce capacitive reactance and inductive reactance used for signal tuning and transformation.