Frequency

Prof. Dr. Thorsten Jungmann (last updated 2025-09-03)

Frequency (German: Frequenz) describes the number of periodic events per unit of time. It indicates how often a recurring event repeats within a given time span.

1 Quantity symbol and unit

The quantity symbol is $f$. The unit is the hertz ($\mathrm{Hz}$), named after Heinrich Rudolf Hertz. One hertz corresponds to one oscillation per second:

$$1\mathrm{Hz}=1{\mathrm{s}}^{-1}$$

The frequency is the reciprocal of the period:

$$f=\frac{1}{T}$$

where $T$ is the period.

2 Practical and worked examples

• The mains frequency in European power grids is $50\mathrm{Hz}$; in North America it is $60\mathrm{Hz}$.
• VHF broadcasting operates in the range from $87.5$ to $108\mathrm{MHz}$.
• Wi-Fi uses frequencies around $2.4\mathrm{GHz}$ and $5\mathrm{GHz}$.
• Visible light has frequencies of approximately $430$ to $750\mathrm{THz}$.
• The concert pitch A has a frequency of $440\mathrm{Hz}$.

3 Typical orders of magnitude

• Low frequency (LF): $20\mathrm{Hz}$ to $20\mathrm{kHz}$ (audible range)
• Radio frequency (RF): $3\mathrm{kHz}$ to $300\mathrm{GHz}$
• Microwaves: $300\mathrm{MHz}$ to $300\mathrm{GHz}$
• Infrared (IR): $300\mathrm{GHz}$ to $400\mathrm{THz}$
• Visible light: $400$ to $800\mathrm{THz}$
• Ultraviolet (UV): $800\mathrm{THz}$ to $30\mathrm{PHz}$

4 Example phrasings

• ‘The clock frequency of the processor is $3.2\mathrm{GHz}$.’
• ‘The AC grid operates at a frequency of $50\mathrm{Hz}$.’
• ‘The transmitter broadcasts on a frequency of $101.5\mathrm{MHz}$.’

5 Related quantities

• Angular frequency ($\omega$): $\omega =2\pi \cdot f$
• Wavelength ($\lambda$): $\lambda =\frac{c}{f}$ for electromagnetic waves
• Rotational frequency ($n$): In generators, the rotational frequency determines the frequency generated.

6 Relevant components

• Capacitor
• Inductor
• Transformer
• Generator