Wave properties: amplitude, wavelength and frequency
A wave's speed equals its frequency times its wavelength, so for a wave travelling at a fixed speed, a higher frequency always means a shorter wavelength.
Practise this conceptA wave's speed equals its frequency multiplied by its wavelength — how many oscillations pass a point each second, times how much space each one takes up. Get the speed and one of the other two, and the third falls straight out.
For a wave whose speed is fixed by the medium it travels through — like sound in air, or light in a vacuum — frequency and wavelength are locked in a seesaw. Raise the frequency and the wavelength must shrink to match, since the speed itself can't budge; that's a direct consequence of the same equation, not a separate rule to memorise.
It's tempting to think that changing a wave's amplitude — how big its oscillations are — should also change its frequency or speed, but amplitude is independent of both. A loud sound and a quiet sound of the same pitch share the same frequency and travel at the same speed; only their amplitude differs.
Key ideas
Requires: Waves and oscillations
Unlocks: Electromagnetic waves, Interference and diffraction, Photons and quanta, Polarization of light
Formulas
| Symbol | Name | Unit |
|---|---|---|
| speed | m/s (metre per second) | |
| frequency | Hz (hertz) | |
| wavelength | m (metre) |
Common misconceptions
- A wave's speed depends on its frequency, so changing the frequency changes the speed.
- Increasing a wave's amplitude increases its frequency.
- Wavelength and period measure the same thing.