Wave properties · Grade 6

Waves carry energy from place to place without carrying the material along. In a transverse wave (light, ripples, waves on a string) the vibrations are at right angles to the direction of travel; in a longitudinal wave (sound) they are along it. Every wave obeys the same equation: speed = frequency × wavelength.

Key facts

  • Amplitude: from the rest line to a crest. Wavelength λ: from one crest to the next.
  • Frequency f: waves per second (Hz). Period T = 1 ÷ f.
  • v = f λ.
  • Transverse: vibrations ⊥ direction of travel. Longitudinal: vibrations ∥ direction of travel.
  • When a wave changes medium, its frequency stays the same; speed and wavelength change.
  • Phase difference = (separation ÷ λ) × 360°.

Worked examples

Example 1

The diagram shows 3 complete waves across 1.2 m. The frequency is 5 Hz. Find the wavelength and speed.

Answer: λ = 0.4 m, v = 2 m/s

Example 2

A radio station broadcasts at 100 MHz. Radio waves travel at 3.0 × 10⁸ m/s. Find the wavelength.

Answer: 3.0 m

Example 3

Waves of wavelength 2.0 m travel at 3.0 m/s, then enter shallow water where they slow to 1.5 m/s. Find the new wavelength.

Answer: 1.0 m

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