# Sinusoidal Waveform Terminology - AC Circuits

### AC Circuits - Sinusoidal Waveform Terminology:

Amplitude:
The amplitude of sine wave is the maximum value (V/I) reached during a positive or negative alternation.
Peak value:
It denotes the maximum value of the alternative quantity reached during a positive or negative direction.
It is denoted as V, Im

Instantaneous value:
The value of voltage or current at a particular instant (time) is known as instantaneous value.
Generally it is denoted by small alphabet(v for voltage and i for current).

Cycle:
One complete set of positive and negative values of an alternating quantity is called cycle.
ie during one cycle the wave from trace 0 to +max to 0 to -max to 0.

Period:
The time taken for one cycle is known as time period or periodic time.(T).

Its unit is time in seconds
Frequency:
No of cycles made in one second is called as frequency of the alternating quantity.
It is denoted by f.
The unit is Hertz or cycles/second
Peak Value:
The maximum value of an alternating quantity (It may be a current or voltage) during a cycle is called its peak value.
Scalar quantity:
A quantity which has only magnitude but no direction ( ex. Resistance)
Vector quantity:
A quantity which has both direction and magnitude (ex. Force)

Phase:
The development of an AC quantity through different stages as known as phase.

In-Phase:
When two alternating quantities reach their maximum and minimum simultaneously, then these quantities are called as in-phase.

Out of Phase:
When two alternating quantities do not attain their maximum and minimum values simultaneously then they are at out of phase. It is also known as Phase difference.

Phase Angle:
It is an angular displacement between two alternating quantities.

Average Value:
The arithmetical average of all the values of an alternating quantity over one cycle is called as average value.
For sine waveform
IAvg = (2/π)Im = 0.637Im

Root Mean Square (RMS) Value:
The rms value of an alternating current is defined as that steady current which when flowing through a given resistance for a given time produces the same amount of heat as produced by the alternating current when flowing through the same resistance for the same time.
For sine waveform
VRMS =(1√2)* Vm  = 0.707Vm
IRMS =(1√2)* Im  = 0.707Im

Peak Factor:
It is defined as the ratio of the peak or maximum value, to the r.m.s. value, of a waveform.
For sine waveform = Vm /0.707V = 1/0.707 = 1.414

Form Factor:
It is defined as the ratio of the r.m.s. value to the average value.
Form Factor = RMS value  / Average Value
For sine waveform = 0.707 / 0.637 = 1.11