The definitions of frequency, amplitude, wavelength, cycle, and period should be known by all electrical professionals. Below I will give you the definitions and comparisons of these important terms. It will make your life easier.
AC frequency is the number of cycles per second in an alternating current (AC) sine wave. In other words, frequency is the number of times a sine wave repeats a positive and a negative cycle.
Frequency is typically used to describe electrical equipment operation. Some common frequency ranges are:
Power line frequency (For example Most of Europe is 50 Hz and America is 60 Hz)
Low frequency: 300 kHz to 3 megahertz (MHz).
Medium frequency: 3-30 MHz.
High frequency: 30-300 MHz.
Airband range: 118 to 137 MHz
Audio frequency range: 15 Hz to 20 kHz (the range of human hearing).
Radiofrequency: 30-300 kHz.
The standard unit for frequency is the Hertz (Hz), deﬁned as events or cycles per second. The frequency of electrical signals is often measured in multiples of hertz, including kilohertz (kHz), megahertz (MHz), or gigahertz (GHz), where 1 kHz equals one thousand (10³) events per second, 1 MHz equals one million (10⁶) events per second, and 1 GHz equals one billion (10⁹) events per second.
In 1930, International Electrotechnical Commission (IEC) honored Heinrich Rudolf Hertz by naming the unit that is used to measure frequency.
To measure the frequency, the number of times an event occurs in a given time interval is counted, then this number is divided by the time interval.
f = 1 / T
Another formula of the frequency is:
f = c / λ
c: Wave velocity (electromagnetic wave velocity = speed of light = 3 x 10 m/sec)
The period is the length of time in seconds that the waveform takes to repeat itself from start to finish. It is indicated by the letter “T”. It is inversely proportional to the frequency. Its unit is second.
Amplitude can simply be defined in several ways:
- The amplitude is half the vertical distance from the crest of a wave to its trough.
- It can also be defined as the maximum level in a periodic movement.
- Amplitude is the maximum absolute value of a periodically varying quantity.
Wavelength is the distance between repeating units of a wave group. It is denoted as a symbol with the letter lambda (λ).
Wavelength has an inversely proportional relationship with frequency. The longer the wavelength, the lower the frequency.
Calculation of wavelength is:
λ = v / f
v: Wave velocity
In most cases, the wave velocity (v) is chosen as the velocity of light (c) with the assumption that the wave is traveling in space. In this case, the formula would be as follows:
λ = c / f
c: Velocity of light
The wavelength and period relationship is as follows:
λ = T x v
v: Wave velocity
A cycle is a full alternating current or voltage wave. In other words, the rise of a curve starting from zero to a positive maximum value, decreasing again to zero and negative maximum value, and then reaching zero again is called “cycle”.
Difference between cycle and period:
The time taken for a cycle to complete is called a period. So a cycle is a full wave. The period is the length of time in seconds that the waveform takes to repeat itself from start to finish.