PHYSICS NOTES 4U / DETAILED TOPIC SERIES
Waves and optics / patterns to principles
AQA A-level Physics 7408 • Section 3.3 • Review edition
Detailed topic pack / AQA 7408 section 3.3
Wave questions connect local oscillation to energy propagation and use phase to explain
patterns. Keep a displacement-time graph distinct from a snapshot along space, then use path
difference to reason about interference.
Progressive and stationary waves, polarisation, string harmonics, interference, diffraction
gratings, refraction and step-index fibres. Includes required practicals 1 and 2, original
wave snapshots and 16 original tasks with solutions.
Find it Page
Progressive waves, phase and graph choice 2
Transverse, longitudinal and polarisation 3
Stationary-wave formation / original snapshots 4
Strings, harmonics and required practical 1 5
Coherence and interference 6
Double slits and required practical 2 7
Single slit and diffraction gratings 8
Grating derivation and measurement 9
Refraction and total internal reflection 10
Step-index fibres and pulse broadening 11
Practice 1--16
Worked solutions 1--16
Checklist and sources 16
Original independent revision notes, not produced or endorsed by AQA. Review edition. Practice has no official
mark allocations. Quantum phenomena are covered separately.
Independent revision notes • Edition 1.0 for review • October 2026 1
,PHYSICS NOTES 4U / DETAILED TOPIC SERIES
Progressive waves / space versus time
AQA A-level Physics 7408 • Section 3.3 • Review edition
A progressive wave transfers energy through a medium or space. In a mechanical wave
particles oscillate around equilibrium; they do not travel with the pattern over a wavelength
each cycle. Electromagnetic waves involve oscillating fields and need no material medium.
Quantity Meaning / unit
Amplitude A Maximum displacement from equilibrium / m
Period T Time for one complete oscillation / s
Frequency f Cycles per second; f=1/T / Hz
Wavelength λ Shortest distance between points in phase / m
Wave speed v Propagation speed of the pattern; v=fλ / m s⁻¹
Phase
Phase describes position within an oscillation cycle. One cycle=360°=2π radians. For points on
the same progressive wave at one instant, phase difference magnitude=2πΔx/λ, modulo
complete cycles. For one point sampled at two times, Δϕ=2πΔt/T. In phase means equal stages
of the cycle, not just equal displacement at one moment.
Example: λ=0.80 m and separation 0.20 m gives a quarter cycle: 90° or π/2 rad. Points
separated by 0.80 m are one full cycle apart and in phase. Points λ/2 apart are in antiphase.
Choose the right graph
Displacement against distance is a snapshot: horizontal separation between crests gives λ.
Displacement against time follows a fixed point: crest-to-crest time gives T. The gradient of a
time graph is particle velocity, not wave propagation speed; the two are different quantities.
Calculation: f=250 Hz and λ=1.36 m give v=340 m s−1. T=1/250=4.00 ms. A particle's
amplitude does not enter v=fλ.
For a travelling wave, direction of particle motion at a chosen instant depends on both spatial slope and
propagation direction. A snapshot without the travel direction cannot fix the velocity sign.
Independent revision notes • Edition 1.0 for review • October 2026 2
, PHYSICS NOTES 4U / DETAILED TOPIC SERIES
Wave types / polarisation tests
AQA A-level Physics 7408 • Section 3.3 • Review edition
Wave Oscillation relative to propagation Example
Transverse Perpendicular String displacement; EM electric/magnetic
fields
Longitudinal Parallel Sound pressure/displacement in air
A compression in sound has particles closer together and higher pressure; a rarefaction has
them farther apart. Particle motion is back and forth, not a permanent stream moving from the
source to receiver. Electromagnetic waves of all frequencies travel at c=3.00 × 10⁸ m s−1 in
vacuum.
Polarisation
An unpolarised transverse wave has oscillations in different transverse directions. A
plane-polarised wave oscillates in one plane. A polarising material transmits one permitted
component of electric-field oscillation. Two crossed ideal polarisers block transmission; aligned
transmission axes allow it.
Evidence: only transverse waves have multiple possible oscillation directions
perpendicular to travel that can be selected. Longitudinal sound in air cannot be
plane-polarised in this way. Polarisation is therefore evidence for the transverse nature of
light.
Applications
Polaroid sunglasses reduce strongly polarised reflected glare by selecting an appropriate
transmission direction. For radio/microwave waves, a receiving aerial responds strongly when
aligned with the electric-field oscillation and weakly when perpendicular. Rotate it to test
polarisation.
A polariser generally reduces intensity, but it does not lower the wave's frequency or change
photon energy. This section requires qualitative angle reasoning, not Malus's law.
An ideal crossed pair gives zero transmitted intensity; real materials may leak some light. Never use sunglasses or
classroom polarisers as eye protection for laser viewing.
Independent revision notes • Edition 1.0 for review • October 2026 3
Waves and optics / patterns to principles
AQA A-level Physics 7408 • Section 3.3 • Review edition
Detailed topic pack / AQA 7408 section 3.3
Wave questions connect local oscillation to energy propagation and use phase to explain
patterns. Keep a displacement-time graph distinct from a snapshot along space, then use path
difference to reason about interference.
Progressive and stationary waves, polarisation, string harmonics, interference, diffraction
gratings, refraction and step-index fibres. Includes required practicals 1 and 2, original
wave snapshots and 16 original tasks with solutions.
Find it Page
Progressive waves, phase and graph choice 2
Transverse, longitudinal and polarisation 3
Stationary-wave formation / original snapshots 4
Strings, harmonics and required practical 1 5
Coherence and interference 6
Double slits and required practical 2 7
Single slit and diffraction gratings 8
Grating derivation and measurement 9
Refraction and total internal reflection 10
Step-index fibres and pulse broadening 11
Practice 1--16
Worked solutions 1--16
Checklist and sources 16
Original independent revision notes, not produced or endorsed by AQA. Review edition. Practice has no official
mark allocations. Quantum phenomena are covered separately.
Independent revision notes • Edition 1.0 for review • October 2026 1
,PHYSICS NOTES 4U / DETAILED TOPIC SERIES
Progressive waves / space versus time
AQA A-level Physics 7408 • Section 3.3 • Review edition
A progressive wave transfers energy through a medium or space. In a mechanical wave
particles oscillate around equilibrium; they do not travel with the pattern over a wavelength
each cycle. Electromagnetic waves involve oscillating fields and need no material medium.
Quantity Meaning / unit
Amplitude A Maximum displacement from equilibrium / m
Period T Time for one complete oscillation / s
Frequency f Cycles per second; f=1/T / Hz
Wavelength λ Shortest distance between points in phase / m
Wave speed v Propagation speed of the pattern; v=fλ / m s⁻¹
Phase
Phase describes position within an oscillation cycle. One cycle=360°=2π radians. For points on
the same progressive wave at one instant, phase difference magnitude=2πΔx/λ, modulo
complete cycles. For one point sampled at two times, Δϕ=2πΔt/T. In phase means equal stages
of the cycle, not just equal displacement at one moment.
Example: λ=0.80 m and separation 0.20 m gives a quarter cycle: 90° or π/2 rad. Points
separated by 0.80 m are one full cycle apart and in phase. Points λ/2 apart are in antiphase.
Choose the right graph
Displacement against distance is a snapshot: horizontal separation between crests gives λ.
Displacement against time follows a fixed point: crest-to-crest time gives T. The gradient of a
time graph is particle velocity, not wave propagation speed; the two are different quantities.
Calculation: f=250 Hz and λ=1.36 m give v=340 m s−1. T=1/250=4.00 ms. A particle's
amplitude does not enter v=fλ.
For a travelling wave, direction of particle motion at a chosen instant depends on both spatial slope and
propagation direction. A snapshot without the travel direction cannot fix the velocity sign.
Independent revision notes • Edition 1.0 for review • October 2026 2
, PHYSICS NOTES 4U / DETAILED TOPIC SERIES
Wave types / polarisation tests
AQA A-level Physics 7408 • Section 3.3 • Review edition
Wave Oscillation relative to propagation Example
Transverse Perpendicular String displacement; EM electric/magnetic
fields
Longitudinal Parallel Sound pressure/displacement in air
A compression in sound has particles closer together and higher pressure; a rarefaction has
them farther apart. Particle motion is back and forth, not a permanent stream moving from the
source to receiver. Electromagnetic waves of all frequencies travel at c=3.00 × 10⁸ m s−1 in
vacuum.
Polarisation
An unpolarised transverse wave has oscillations in different transverse directions. A
plane-polarised wave oscillates in one plane. A polarising material transmits one permitted
component of electric-field oscillation. Two crossed ideal polarisers block transmission; aligned
transmission axes allow it.
Evidence: only transverse waves have multiple possible oscillation directions
perpendicular to travel that can be selected. Longitudinal sound in air cannot be
plane-polarised in this way. Polarisation is therefore evidence for the transverse nature of
light.
Applications
Polaroid sunglasses reduce strongly polarised reflected glare by selecting an appropriate
transmission direction. For radio/microwave waves, a receiving aerial responds strongly when
aligned with the electric-field oscillation and weakly when perpendicular. Rotate it to test
polarisation.
A polariser generally reduces intensity, but it does not lower the wave's frequency or change
photon energy. This section requires qualitative angle reasoning, not Malus's law.
An ideal crossed pair gives zero transmitted intensity; real materials may leak some light. Never use sunglasses or
classroom polarisers as eye protection for laser viewing.
Independent revision notes • Edition 1.0 for review • October 2026 3
