Wave behaviour
Transverse vs longitudinal
- Transverse: oscillations perpendicular to direction of energy transfer (water surface, light, all EM waves, S-waves).
- Longitudinal: oscillations parallel to direction of energy transfer (sound, P-waves) — show compressions and rarefactions.
In both, energy and information travel without net particle movement.
Wave properties
- Wavelength λ — distance between two consecutive points in phase (m).
- Frequency f — number of complete waves per second (Hz).
- Period T — time for one cycle (s); T = 1/f.
- Amplitude — maximum displacement from equilibrium (m).
- Speed v — distance travelled per second.
The wave equation: v = f × λ.
✦Worked example— Worked examples
A water wave has frequency 0.4 Hz and wavelength 1.5 m. v = 0.4 × 1.5 = 0.6 m/s.
A sound at 256 Hz in air (v = 340 m/s): λ = 340 / 256 = 1.33 m.
Reflection, refraction, absorption, transmission
When a wave meets a boundary one or more of these can occur:
- Reflection — wave bounces back; angle of incidence = angle of reflection (smooth surface) → mirror image; rough surface → diffuse scattering.
- Refraction — wave changes speed and bends as it crosses into a different medium (light slows in glass; bends towards the normal).
- Absorption — wave's energy transfers to the medium (microwave heating water).
- Transmission — wave passes through.
The total energy is conserved across all four pathways.
OCR PAG P5 — measuring wave speed
Two methods you must know:
- Ripple tank: measure λ with a ruler and f with a stroboscope; v = fλ.
- Sound: timing echoes off a wall a known distance away; v = 2d / t.
OCR exam tip
A graph of displacement vs distance shows λ on the x-axis (peak to peak); displacement vs time shows T (period) on the x-axis. Mis-reading these is the most common 1-mark loss.
AI-generated · claude-opus-4-7 · v3-ocr-combined-science-leaves