Waves and Sound
A wave transfers energy without transferring matter. Candidates must know amplitude, wavelength λ, frequency f, period T = 1/f, and the wave equation v = fλ. Transverse waves oscillate perpendicular to propagation; longitudinal waves, including sound, oscillate along the direction of propagation. Sound requires a material medium and travels fastest in solids, slower in liquids, and slowest in gases.
Wave behaviour includes reflection, refraction, diffraction and interference. When a wave crosses into a new medium, its frequency stays constant while its speed and wavelength change. Standing waves have nodes and antinodes; resonance occurs when a system is driven at a natural frequency. Sound intensity is power per unit area, and the decibel scale is logarithmic: dB = 10 log₁₀(I/I₀). The Doppler effect is the change in observed frequency caused by relative motion between source and observer. Ultrasound has frequencies above human hearing.
Traps: frequency is unchanged on refraction; sound cannot travel through a vacuum; doubling intensity adds about 3 dB, not 2 dB; an echo timing must be halved to find one-way distance; and period is the reciprocal of frequency.
Worked example: a sound wave has frequency 440 Hz and speed 340 m/s. Its wavelength is λ = v/f = 340/440 ≈ 0.773 m. Its period is T = 1/440 ≈ 2.27 ms. For an echo returning after 0.60 s, the one-way distance is d = vt/2 = 340 × 0.60 / 2 = 102 m.