GCSE Physics Waves Notes
Waves transfer energy without transferring matter. Learn the properties and the wave speed equation and you can describe and calculate any wave.
Key concepts
- Transverse wave
- Oscillations are perpendicular to the direction of energy transfer, e.g. light and water waves.
- Longitudinal wave
- Oscillations are parallel to the direction of energy transfer, with compressions and rarefactions, e.g. sound.
- Frequency and wavelength
- Frequency is the number of waves per second (Hz); wavelength is the distance between two matching points (m).
- Waves transfer energy, not matter — a floating object bobs up and down but doesn't travel with the wave.
- Amplitude is the maximum displacement from rest; larger amplitude means more energy.
- The period is the time for one complete wave: T = 1 ÷ f.
Key formulas
Wave speed
v = f × λ
speed (m/s) = frequency (Hz) × wavelength (m).
Period
T = 1 ÷ f
period (s) = 1 ÷ frequency (Hz).
Required practicals
- Measure the frequency, wavelength and speed of waves in a ripple tank and on a stretched string.
Worked example
A wave has a frequency of 50 Hz and a wavelength of 0.2 m. Find its speed.
- 1Write the equation: v = f × λ.
- 2Substitute: v = 50 × 0.2.
- 3Multiply: v = 10.
- 4Add the unit: v = 10 m/s.
Answer: v = 10 m/s
Common mistakes
✗ Confusing transverse and longitudinal waves.
✓ Transverse: oscillations at right angles (light). Longitudinal: oscillations along the wave (sound).
✗ Measuring amplitude from top to bottom of the wave.
✓ Amplitude is from the rest position to the peak, not peak to trough.
✗ Mixing up frequency (Hz) and period (s).
✓ They are reciprocals: T = 1 ÷ f.
Quick check
Try these, then reveal the answers.
Is sound a transverse or longitudinal wave?Reveal answer
Longitudinal.
A wave has a period of 0.5 s. Find its frequency.Reveal answer
f = 1 ÷ 0.5 = 2 Hz
What does a wave transfer?Reveal answer
Energy, not matter.
Exam tips
- State the type of wave first — it often decides the rest of the answer.
- Keep frequency in Hz and wavelength in m before using v = fλ.
- Amplitude relates to energy; wavelength and frequency relate to speed.
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Frequently asked questions
What is the difference between transverse and longitudinal waves?+
In transverse waves the oscillations are perpendicular to the direction of travel (e.g. light); in longitudinal waves they are parallel, forming compressions and rarefactions (e.g. sound).
Do waves transfer matter?+
No — waves transfer energy from place to place, but the particles or the medium only oscillate about a fixed position.
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