Waves & Quantum is a core part of A-Level Physics. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Transverse & longitudinal wavesVibrations perpendicular (light) or parallel (sound) to travel.
Frequency & wavelengthNumber of waves per second and the length of one wave.
Wave speedv = f × λ, the speed a wave travels.
AmplitudeMaximum displacement from the rest position; relates to energy.
Electromagnetic spectrumRadio to gamma; all travel at the speed of light in a vacuum.
Reflection & refractionWaves bounce off surfaces or change direction when changing medium.
WavelengthDistance between two adjacent identical points.
FrequencyNumber of cycles per second, measured in Hz.
TransverseOscillations perpendicular to wave direction.
LongitudinalOscillations parallel to wave direction.
PolarisationRestricting transverse oscillations to one plane.
Refractive indexn = c / v in the medium.
Snell's lawn1 sin theta1 = n2 sin theta2.
Critical angleAngle giving theta2 = 90°: sin theta_c = n2/n1.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
Do all points on a stationary wave oscillate with the same amplitude?✗ Yes — amplitude is constant along the wave, as in a progressive wave. ✓ No — amplitude varies from zero at the nodes to a maximum at the antinodes.
When a wave refracts into a new medium, which property stays the same?✗ The wavelength stays the same and the frequency changes. ✓ The frequency — the speed and wavelength change together.
Can sound waves be polarised?✗ Yes — any wave can be polarised with the right filter. ✓ No — polarisation applies only to transverse waves, and sound is longitudinal.
Which type of wave can be polarised?✗ Longitudinal waves only ✓ Transverse waves only
At a node on a stationary wave:✗ The amplitude is at its maximum. ✓ The displacement is always zero.
Practise Waves & Quantum — free games
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