Knowledge Organiser: Wave Properties
Key Terms
- Amplitude: max displacement from rest (m)
- Frequency: waves per second (Hz)
- Wavelength: distance crest to crest (m)
- Period: time for one wave (s)
- Transverse: vibration perpendicular to travel
- Longitudinal: vibration parallel to travel
Key Facts
- All waves transfer energy, not matter
- Sound = longitudinal; light = transverse
- Frequency is set by the source, unchanged by medium
- Speed changes at boundaries; wavelength adjusts
- Higher frequency → shorter wavelength (same speed)
Key Equations
- v = f × λ (wave speed)
- T = 1/f (period)
- f = 1/T (frequency)
Exam Tips
- Amplitude = crest to rest, NOT crest to trough
- Show all working in wave calculations
- State type + give example for full marks
- Compressions + rarefactions = longitudinal only
Common Mistakes
- Measuring amplitude as crest to trough: Amplitude is the distance from the rest position to the crest (or trough) — not the full crest-to-trough distance, which is twice the amplitude
- Confusing wavelength and period: Wavelength (λ) is a distance (m); period (T) is a time (s) — they are different quantities even though both relate to one complete wave cycle
- Saying particles travel with the wave: In a wave, particles oscillate about their rest position — they do not travel with the wave; only energy is transferred
- Confusing transverse and longitudinal: Transverse waves have vibrations perpendicular to wave direction (light, water); longitudinal waves have vibrations parallel to wave direction (sound)
- Getting the wave equation wrong: v = f × λ — wave speed equals frequency times wavelength; not frequency divided by wavelength
Memory Aid
- To remember wave types: "Transverse = T-shirt shake" — imagine shaking a T-shirt side to side; the wave goes along but the fabric moves sideways (perpendicular). Longitudinal = "along" — the vibration goes along the same direction as the wave.
- Wave equation triangle:
- Draw a triangle with v on top, and f and λ on the bottom. Cover the quantity you want to find: cover v → f × λ; cover f → v ÷ λ; cover λ → v ÷ f.