IGCSE Physics Waves Notes
Waves transfer energy without transferring matter. Learn the wave equation and the difference between transverse and longitudinal waves.
Key concepts
- Transverse wave
- Oscillations are perpendicular to the direction of energy transfer, e.g. light and water ripples.
- Longitudinal wave
- Oscillations are parallel to the direction of energy transfer, e.g. sound — with compressions and rarefactions.
- Frequency
- The number of complete waves passing a point per second, measured in hertz (Hz).
- Wavelength is the distance between two matching points on adjacent waves.
- Amplitude is the maximum displacement from the rest position.
- Wave speed depends on the medium; frequency is set by the source.
Key formulas
Wave equation
v = f × λ
speed = frequency × wavelength.
Frequency & period
f = 1 ÷ T
T = time for one wave.
Required practicals
- Measure the speed of water waves in a ripple tank.
- Measure the frequency and wavelength of waves on a stretched string.
Worked example
A wave has a frequency of 50 Hz and a wavelength of 4 m. Find its speed.
- 1Write the wave equation: v = f × λ.
- 2Substitute: v = 50 × 4.
- 3Calculate: v = 200.
- 4State the unit: v = 200 m/s.
Answer: v = 200 m/s
Common mistakes
✗ Confusing amplitude with wavelength.
✓ Amplitude is height from rest; wavelength is the horizontal length of one wave.
✗ Thinking waves transfer matter.
✓ Waves transfer energy and information, not the medium itself.
✗ Mixing up transverse and longitudinal.
✓ Transverse = perpendicular oscillation; longitudinal = parallel oscillation.
Quick check
Try these, then reveal the answers.
State the wave equation.Reveal answer
v = f × λ.
Is sound transverse or longitudinal?Reveal answer
Longitudinal.
What is the unit of frequency?Reveal answer
The hertz (Hz).
Exam tips
- Convert units before substituting (e.g. kHz to Hz).
- Label wavelength and amplitude correctly on a wave diagram.
- State the medium when discussing wave 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 energy transfer; in longitudinal waves they are parallel.
Do waves carry matter?+
No — waves transfer energy and information without transferring the medium itself.
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