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Wavelength, frequency, speed
Beginner
Fundamental wave relation.
v = fλv = fλ: the wave advances one wavelength in one period. The speed is set by the medium; frequency by the source.
A 440 Hz tone in air (343 m/s) has λ = 0.78 m.
When the wave enters a new medium, f stays the same and λ changes.
In more detail
Wavelength λ is the distance between successive identical points on a wave, frequency f is the number of cycles per second, and speed v is their product, v = fλ.
Real-world uses
- Radio stations are identified by their frequency, and wavelength follows from speed.
- Sonar systems choose wavelengths suited to the depth of the water.
- A radio station at 100 MHz with a wave speed of 3 × 10⁸ m/s has a wavelength of 3 metres, which sets the antenna length.
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Frequently asked questions
What is the unit of frequency?
The hertz, one cycle per second.
If frequency increases, what happens to wavelength?
For a fixed speed, the wavelength decreases, since v equals fλ.
Does frequency change when a wave enters a new medium?
No. The frequency stays the same, but the speed and wavelength change together.
Related topics in Waves & Sound
Mechanical vs electromagnetic waves · Transverse waves · Longitudinal waves · Amplitude and intensity · Wave equation (travelling) · Wave number