Chapter 7. Waves, Sound and Light

Waves transfer energy without transferring matter. Transverse waves oscillate perpendicular to their direction of travel (light); longitudinal waves oscillate along it (sound) [8][9].

Wave properties: amplitude, wavelength (λ), frequency (f, in hertz) and speed. v = fλ.

Sound needs a medium. In air at about 20 °C it travels at roughly 343 m/s, faster in liquids and solids. Pitch depends on frequency; loudness depends on amplitude.

Light is an electromagnetic wave. In a vacuum it travels at exactly 299,792,458 m/s, about 3 × 10⁸ m/s [5]. It also behaves as particles (photons).

The electromagnetic spectrum, from longest to shortest wavelength: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray. Visible light runs from red (longest wavelength) to violet (shortest).

Wave behaviours: reflection, refraction (bending when changing medium), diffraction, interference and absorption. Lenses and mirrors use reflection and refraction to form images.

Review: A sound wave has frequency 440 Hz in air at 343 m/s. Find its wavelength. (Answer: 343/440 ≈ 0.78 m.)