What Is Frequency?
Frequency measures how often a repeating event occurs per unit of time. In physics, it typically refers to the number of wave cycles passing a fixed point per second, measured in Hertz (Hz). One Hertz equals one cycle per second. Frequency is inversely related to period: a shorter period means a higher frequency.
Frequency appears throughout physics, from sound waves and electromagnetic radiation to mechanical vibrations and AC electrical circuits. Understanding frequency is essential for engineering, music, telecommunications, and quantum mechanics.
Frequency Formulas
Common Frequencies
| Phenomenon | Frequency | Period |
|---|---|---|
| Human Heartbeat | 1-2 Hz | 0.5-1 s |
| AC Power (US) | 60 Hz | 16.67 ms |
| Middle C (Music) | 261.6 Hz | 3.82 ms |
| FM Radio | 88-108 MHz | ~10 ns |
| Wi-Fi (2.4 GHz) | 2.4 GHz | 0.42 ns |
| Visible Light | 430-770 THz | ~1 fs |
Applications
- Music: Frequency determines the pitch of a musical note. Concert A is defined as 440 Hz.
- Radio: Different frequency bands are allocated for AM, FM, TV, and cellular communications.
- Medicine: Ultrasound imaging uses frequencies from 2 to 18 MHz.
- Electronics: Clock frequencies in processors determine computation speed.
Frequently Asked Questions
What is the difference between frequency and period?
Frequency and period are reciprocals of each other. Period (T) is the time for one complete cycle, while frequency (f) is the number of cycles per second. If a wave has a period of 0.5 seconds, its frequency is 1/0.5 = 2 Hz.
What is angular frequency?
Angular frequency (omega) measures rotation rate in radians per second rather than cycles per second. It equals 2 pi times the ordinary frequency. Angular frequency is widely used in physics and engineering for describing oscillatory and rotational motion.
Can frequency be negative?
In standard physics, frequency is always a positive quantity. However, in signal processing and complex analysis, negative frequencies appear as mathematical tools to represent the direction of rotation in phasor notation.