P6 Waves — Section Overview
Waves transfer energy (and sometimes information) without transferring matter. AQA GCSE Physics covers both mechanical waves (sound, water) and electromagnetic waves (light, radio, X-rays), plus some important wave phenomena.
What this section covers
| Sub-topic | Key ideas |
|---|---|
| P6.1 Waves and wave properties | Transverse vs longitudinal; amplitude, wavelength, frequency, period; v = fλ |
| P6.2 EM spectrum | 7 regions from radio to gamma; uses and hazards of each |
| P6.3 Reflection, refraction, absorption | Plane mirrors; Snell's law; total internal reflection; absorbing materials |
| P6.4 Sound | Ultrasound; echoes; speed of sound; hearing range |
| P6.5 Lenses and the eye (Physics-only) | Converging and diverging lenses; focal length; ray diagrams |
| P6.6 Black body radiation | Emission and absorption spectra; greenhouse effect |
Core wave equations
- Wave speed: v = fλ (m/s = Hz × m)
- Period: T = 1/f
- Snell's law: n₁ sin θ₁ = n₂ sin θ₂ (or sin i / sin r = n for air→medium)
Types of wave
Transverse: oscillations perpendicular to energy travel direction (light, EM waves, water surface waves). Shown as a sine curve.
Longitudinal: oscillations parallel to energy travel direction (sound, P-seismic waves). Compressions and rarefactions — cannot be drawn as a sine curve (or can, with understanding it represents pressure variation).
The EM spectrum
From lowest to highest frequency: Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma. All travel at 3 × 10⁸ m/s in a vacuum. Higher frequency = shorter wavelength = more energy per photon = greater ionising ability.
Refraction and TIR
Light bends when it crosses a boundary between media of different optical densities. When moving from a denser to less dense medium, if the angle of incidence exceeds the critical angle, total internal reflection occurs (used in optical fibres and prisms).
Exam focus
- Use v = fλ carefully: watch out for wavelength in nm or cm — convert to metres.
- Know all 7 regions of the EM spectrum and their uses AND hazards.
- For ray diagrams with lenses: draw incident ray parallel to axis, through focal point, and through optical centre.
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