Wave properties

Waves transfer energy without transferring matter. Light and sound are both waves. The wavelength is the length of one full wave, the frequency is how many waves pass each second, and the amplitude is the height from the middle to a peak.

Key facts

  • Wave speed = frequency × wavelength: v = fλ.
  • Frequency is measured in hertz (Hz): waves per second.
  • Sound needs a medium (solid, liquid or gas); light can travel through a vacuum.
  • Sound travels at about 340 m/s in air; light at 300 000 000 m/s.

Worked examples

Example 1

A wave has a frequency of 50 Hz and a wavelength of 2 m. How fast does it travel?

  1. Multiply. v = 50 × 2
  2. So v = 100 m/s

Answer: 100 m/s

Example 2

Thunder is heard 3 s after the lightning. Sound travels at 340 m/s. How far away is the storm?

  1. Light arrives almost instantly, so use the sound’s time. 340 × 3
  2. So 1020 m

Answer: 1020 m