1. What Wavelength Means
Wavelength is one of the key quantities that helps describe a wave. It tells us how long one complete wave cycle is in space. Whether it’s ripples on water, sound in air, or light travelling from a bulb, every wave has a repeating pattern — and the distance before that pattern repeats is the wavelength.
I like to think of wavelength as the ‘length’ of one wave shape before it starts all over again.
2. Definition of Wavelength
Definition: Wavelength is the distance between two corresponding points on consecutive cycles of a wave, such as two crests, two troughs, or two compressions.
It is usually represented by the Greek letter lambda (\( \lambda \)).
3. Wavelength in Transverse Waves
In transverse waves, the motion repeats itself in a pattern of crests (peaks) and troughs (valleys). The wavelength is the horizontal distance between similar points in this pattern.
3.1. How to Identify Wavelength
For a transverse wave, you can measure wavelength as:
- The distance between two adjacent crests.
- The distance between two adjacent troughs.
Both give the same value of \( \lambda \).
3.2. Visual Picture
Imagine shaking a long rope up and down. The repeating peaks that travel along the rope are crests. Measure from one crest to the next — that’s your wavelength.
4. Wavelength in Longitudinal Waves
In longitudinal waves, particles move back and forth, creating compressions and rarefactions instead of crests and troughs. The wavelength is the distance between two successive compressions or two successive rarefactions.
4.1. Example: Sound Wave
When sound travels through air, regions of high pressure (compressions) and low pressure (rarefactions) move forward. The distance from one compression to the next is the sound’s wavelength.
5. Relationship Between Wavelength, Frequency and Speed
Wavelength is linked to how fast a wave moves and how often it repeats. This relationship is given by:
\( v = f\lambda \)
Here:
- \( v \) = wave speed
- \( f \) = frequency
- \( \lambda \) = wavelength
This formula applies to all kinds of waves.
6. Why Wavelength Is Important
Wavelength helps determine the nature and behaviour of a wave. For example:
- Shorter wavelengths in light correspond to colours like blue and violet.
- Longer wavelengths correspond to red and infrared.
- Short sound wavelengths give high-pitched sounds.
- Long sound wavelengths give deep, low-pitched sounds.
Knowing wavelength makes it easier to understand how waves interact, reflect, refract, and interfere.
7. Examples of Wavelength in Real Life
You can see or feel wavelength effects in many places:
- The spacing between ripples in water.
- The distance between bright spots in light interference patterns.
- The pitch difference between a whistle and a drumbeat.
- The spacing of compressions in a slinky when pushed.
In each case, the wavelength describes the size of the repeating pattern.