Wavelength is the distance between two identical adjacent points in a wave. It is typically measured between two easily identifiable points, such as two adjacent crests or troughs in a waveform. While wavelengths can be calculated for many types of waves, they are most accurately measured in sinusoidal waves, which have a smooth and repetitive oscillation.
Wavelength is inversely proportional to frequency. That means if two waves are traveling at the same speed, the wave with a higher frequency will have a shorter wavelength. Likewise, if one wave has a longer wavelength than another wave, it will also have a lower frequency if both waves are traveling at the same speed. The following formula can be used to determine wavelength:
λ = v / ƒ
The lowercase version of the Greek letter "lambda" (λ) is the standard symbol used to represent wavelength in physics and mathematics. The letter "v" represents velocity and "ƒ" represents frequency. Since the speed of sound is roughly 343 meters per second at 68° F (20° C), 343 m/s can be substituted for "v" when measuring the wavelength of sound waves. Therefore, only the frequency is needed to determine the wavelength of a sound wave at 68° F. The note A4 (the A key above middle C) has a frequency of 440 hertz. Therefore, the wavelength of an A4 sound wave at 68° F is 343 m/s / 440 hz, which equals 0.7795 meters, or 77.95 cm.
Waves in the electromagnetic spectrum, such as radio waves and light waves, have much shorter wavelengths than sound waves. Therefore, these wavelengths are typically measured in millimeters or nanometers, rather than centimeters or meters.