Describe the features of a wave in terms of wavefront, wavelength, frequency, crest (peak), trough, amplitude and wave speed

3.1 General Properties of Waves

Wavefront

A wavefront is a line (or surface in 3‑D) that connects points on a wave that are in the same phase. Think of it as the “front” of a ripple when you drop a stone in a pond. All points on the wavefront rise or fall together, like a marching band moving in sync. 🌊

Wavelength (λ)

The wavelength is the distance between two successive crests (or troughs). It’s the “size” of one complete wave cycle. If you imagine a string vibrating, λ is the length of one full bump. 📏

Frequency (f)

Frequency is the number of wave crests that pass a fixed point per second. It’s measured in hertz (Hz). If you tap a drum at a steady rhythm, the faster you tap, the higher the frequency. 🎵

Crest and Trough

  • Crest (peak) – the highest point of a wave.
  • Trough – the lowest point of a wave.

Amplitude (A)

Amplitude is the maximum displacement from the equilibrium position. It tells us how “strong” or “intense” the wave is. A bigger amplitude means a louder sound or a higher light intensity. 🎈

Wave Speed (v)

Wave speed is how fast a wave travels through a medium. The basic relationship is:

\$v = \lambda f\$

So if you know the wavelength and the frequency, you can find the speed, and vice‑versa. Think of it like a runner’s speed: distance divided by time. 🏃‍♂️

Quick Reference Table

PropertyDefinitionExample
WavefrontLine of equal phaseRipples from a stone drop
Wavelength (λ)Distance between two crests≈0.5 m for a guitar string
Frequency (f)Crests per second440 Hz (A note)
Amplitude (A)Maximum displacement1 cm for a gentle wave
Wave Speed (v)Distance per unit time≈340 m/s for sound in air

Quick Practice

  1. Draw a wave and label the crest, trough, amplitude, and wavelength.
  2. If a wave has a frequency of 20 Hz and a wavelength of 2 m, calculate its speed.
  3. Describe how amplitude relates to the loudness of a sound.