Frequency describes how often an event repeats per time. Definition, units, ranges, conversion, measurement, and applications.
What is Frequency?
f = cycles/time; T = time/cycle. Relation: f = 1/T. SI unit: hertz (Hz).
Key Concept:
f = 1/T. Higher f → shorter period.
Common Frequency Ranges
Audible Sound
20 Hz – 20 kHz
Typical human hearing.
Musical Notes
16.35 – 7,902.13 Hz
Piano; A4 = 440 Hz.
Radio Waves
3 kHz – 300 GHz
Broadcasting and comms.
Visible Light
430–750 THz
Visible EM spectrum.
Units of Frequency
SI Units
- Hz
- kHz
- MHz
- GHz
- THz
Other Units
- RPM (1/60 Hz)
- cps (≈ Hz)
- BPM
- rad/s (ω = 2πf)
Frequency Conversion Table
| Unit | Hertz (Hz) | RPM | rad/s |
|---|---|---|---|
| 1 Hz | 1 | 60 | 6.283 |
| 1 RPM | 0.0167 | 1 | 0.1047 |
| 1 rad/s | 0.1592 | 9.549 | 1 |
Measuring Frequency
Frequency counter
Counts cycles in a time gate.
Oscilloscope
Period → frequency.
Spectrum analyzer
Amplitude vs frequency.
Applications of Frequency
Communications
- Radio/TV
- Mobile networks
- Wi‑Fi/Bluetooth
- Satellites
Music/Audio
- Tuning
- EQ
- Noise cancelation
- Compression
Medical
- Ultrasound
- Heart rate
- EEG
- MRI
Industrial
- Vibration
- Rotating machinery
- NDT
- Process control
Did You Know?
A4 = 440 Hz is common; some orchestras use 442–445 Hz.
Frequency in Everyday Life
Household Electricity
- North America: 60 Hz
- Most of world: 50 Hz
- Japan: 50/60 Hz
Human Body
- Heart: 1–3 Hz
- Brain waves: 0.5–100 Hz
- Vocal cords: 85–255 Hz
Technology
- Wi‑Fi 2.4/5 GHz
- Bluetooth 2.4 GHz
- Microwave 2.45 GHz
- CPU 1–5 GHz
Practical Tip:
Sample ≥ 2× highest frequency (prefer 2.5–4×) to avoid aliasing.