AQA GCSE Physics 8463: Waves – Revision Notes

Condensed recall for the final weeks. For full explanations and worked examples, use the Waves study guide.

These notes cover Topic 6, Waves (sections 4.6.1 to 4.6.3), of the AQA GCSE Physics (8463) specification, for first teaching 2016 with exams from June 2018 (version 1.1). The topic is examined on Paper 2 at Foundation and Higher tier every May/June. Content marked Higher tier only matches the specification’s “(HT only)” statements.

Test yourself with the Waves practice questions. The course hub is AQA GCSE Physics, the printable checklist lists every statement, and the free diagnostics show where to focus.

Key definitions (4.6.1.1–4.6.1.2)

Term	Definition
Transverse wave	Oscillations perpendicular to the direction of energy transfer (water ripples, all EM waves, S-waves)
Longitudinal wave	Oscillations parallel to the direction of energy transfer; compressions and rarefactions (sound in air, P-waves)
Amplitude	Maximum displacement of a point from its undisturbed position
Wavelength, λ	Distance from a point on one wave to the equivalent point on the adjacent wave
Frequency, f	Number of waves passing a point each second (Hz)
Period, T	Time for one complete wave (s)
Wave speed, v	Speed at which energy is transferred through the medium

Evidence the wave moves, not the medium: a floating object bobs up and down on ripples but stays in place; air particles vibrate about fixed positions as sound passes.

Equations

Equation	Symbols and units	Status
v = f λ	v in m/s, f in Hz, λ in m	Recall
T = 1/f	T in s, f in Hz	Equation sheet
magnification = image height / object height	no units	Equation sheet

Prefixes to convert first: kHz = 10³ Hz, MHz = 10⁶ Hz, GHz = 10⁹ Hz, μs = 10⁻⁶ s, mSv = 10⁻³ Sv.

Method in steps: echo and pulse questions

1. Convert time to seconds.
2. Total distance = speed × time.
3. Distance to the boundary = total distance ÷ 2 (there and back).
4. Give units.

Worked reminder: sonar at 1500 m/s, echo after 0.20 s → 1500 × 0.20 = 300 m → depth 150 m.

Method in steps: wave changing medium

1. Frequency stays the same (set by the source).
2. Find λ in each medium with λ = v / f.
3. Faster medium → longer wavelength.

Required practicals

Practical	What you do	Key points
8: waves in a ripple tank and in a solid	Lamp above tank projects waves; measure across 10 waves and divide; count waves per second or read signal generator. String on vibration generator: each loop = half a wavelength	Measure over many waves to reduce uncertainty; v = f λ
9: reflection and refraction of light	Ray box, block on paper, mark rays with crosses, draw normal, protractor	Angles measured from the normal; darkened room; compare surfaces and substances
10: infrared and surfaces	Leslie cube of hot water; IR detector at equal distance from each face	Matt black best emitter and absorber; shiny silver worst

Boundaries and reflection (4.6.1.3)

• At a boundary a wave may be reflected, absorbed or transmitted.
• Ray diagrams: normal at 90° to the surface; angle of incidence = angle of reflection.
• Specular reflection: smooth surface, single direction. Diffuse: rough surface, scattered.

Sound, ultrasound and seismic waves – Higher tier only (4.6.1.4–4.6.1.5)

• Sound makes the ear drum and other parts vibrate. This only works over a limited frequency range: normal human hearing is 20 Hz to 20 kHz.
• Ultrasound: above 20 kHz. Partly reflected at boundaries between media; echo time gives distance. Used for medical and industrial imaging.
• Echo sounding: high-frequency sound measures water depth and finds objects in deep water.
• P-waves: longitudinal, travel through solids and liquids at different speeds.
• S-waves: transverse, cannot pass through liquids, so the S-wave shadow shows part of the core is liquid.

The electromagnetic spectrum (4.6.2)

Long λ, low f → short λ, high f:

radio | microwave | infrared | visible | ultraviolet | X-ray | gamma

• All transverse; all travel at the same speed in a vacuum or air; continuous spectrum; transfer energy from source to absorber.
• Eyes detect only visible light (red to violet).
• Gamma rays come from changes in the nucleus.

Group	Uses (spec examples)	Hazard
Radio	Television and radio	–
Microwaves	Satellite communications, cooking food	–
Infrared	Electrical heaters, cooking, infrared cameras	–
Visible	Fibre optic communications	–
Ultraviolet	Energy efficient lamps, sun tanning	Premature skin ageing, skin cancer risk
X-rays, gamma	Medical imaging and treatments	Ionising: gene mutation and cancer

Radiation dose (sievert, Sv) measures risk of harm. 1000 mSv = 1 Sv.

Higher tier only:

• Substances absorb, transmit, refract or reflect EM waves differently depending on wavelength.
• Refraction is caused by the change in speed. Wave front diagram: the edge entering the slower medium first slows first, so the wave front turns; wave fronts get closer together.
• Radio waves are produced by oscillations in circuits, and absorbed radio waves induce an alternating current of the same frequency.
• Be ready to explain briefly why each group suits its use.

Refraction ray rule: into a slower (denser) medium, bend towards the normal; into a faster one, away from the normal; along the normal, no bending.

Lenses (4.6.2.5)

• Convex lens: parallel rays meet at the principal focus; lens to principal focus = focal length. Image real or virtual.
• Concave lens: parallel rays spread out as if they came from the principal focus; image always virtual.
• Ray diagrams: a ray parallel to the axis refracts through the principal focus (convex) or as if from the principal focus on the object side (concave); a ray through the centre of the lens goes straight on. Draw the convex lens as a vertical line with outward arrowheads, the concave lens with inward arrowheads.
• Magnification is a ratio: same units (mm or cm) for both heights, no unit on the answer.

Colour (4.6.2.6)

• Each colour has a narrow band of wavelength and frequency.
• Opaque object: colour = wavelengths most strongly reflected; others absorbed. White reflects all; black absorbs all.
• Filters transmit their own colour and absorb the rest.
• Transparent and translucent objects transmit light.

Worked reminder: a white shirt seen through a blue filter looks blue; a red shirt through the same filter looks black.

Black body radiation (4.6.3)

• All objects emit and absorb infrared at any temperature; hotter → more radiation per second.
• Intensity and wavelength distribution depend on temperature.
• Perfect black body: absorbs all incident radiation, reflects and transmits none, and is the best possible emitter.
• Higher tier only: constant temperature means absorbing and emitting at equal rates. Absorbing faster → temperature rises. The Earth’s temperature depends on rates of absorption and emission and on reflection of radiation into space.

Must-know distinctions

• Transverse vs longitudinal: perpendicular vs parallel to energy transfer.
• Amplitude vs wave height: amplitude is half the crest-to-trough height.
• Specular vs diffuse reflection: smooth vs rough surface.
• Real vs virtual image: rays meet vs only appear to meet. Concave lenses give only virtual images.
• Absorbed vs transmitted by a filter: absorbed colours are removed; transmitted colours pass.
• P vs S waves: longitudinal, through liquids vs transverse, not through liquids.

Quick self-test

1. Define wavelength.
2. A wave has a period of 0.040 s. Calculate its frequency.
3. A radio wave has frequency 200 MHz. Calculate its wavelength. (Speed of EM waves = 3.0 × 10⁸ m/s.)
4. Which EM group has the longest wavelength?
5. State the range of normal human hearing. (Higher tier only)
6. A sonar pulse in seawater (1500 m/s) returns after 0.60 s. Calculate the depth. (Higher tier only)
7. An object 1.5 cm tall forms an image 4.5 cm tall. Calculate the magnification.
8. Convert 0.35 mSv to sieverts.
9. Explain why S-waves are not detected on the far side of the Earth from an earthquake. (Higher tier only)
10. What colour does a blue object appear in red light?
11. A body absorbs radiation faster than it emits it. What happens to its temperature? (Higher tier only)
12. A wave has speed 12 m/s and frequency 4.0 Hz. Calculate its wavelength.

Answers

1. The distance from a point on one wave to the equivalent point on the adjacent wave.
2. f = 1/T = 1/0.040 = 25 Hz.
3. λ = 3.0 × 10⁸ / 2.0 × 10⁸ = 1.5 m.
4. Radio waves.
5. 20 Hz to 20 kHz.
6. 1500 × 0.60 = 900 m there and back, so depth = 450 m.
7. 4.5 / 1.5 = 3 (no units).
8. 0.35 / 1000 = 0.00035 Sv (3.5 × 10⁻⁴ Sv).
9. S-waves are transverse and cannot travel through liquid; part of the core is liquid, so they are stopped.
10. Black: it reflects only blue, and there is no blue in red light, so all the light is absorbed.
11. It increases.
12. λ = v / f = 12 / 4.0 = 3.0 m.

Where marks are usually lost

• Amplitude read from crest to trough instead of from the middle line.
• Echo distances not halved, or halved twice when the question already gives a one-way distance.
• MHz, GHz or μs used without converting, giving answers out by powers of ten.
• Stating that frequency changes when sound enters water or steel.
• Ray diagrams without a ruled normal, or angles measured from the surface.
• EM spectrum groups in the wrong order, especially ultraviolet and infrared swapped.
• Saying X-rays “burn” cells instead of stating they are ionising and can cause mutation and cancer.
• Giving magnification a unit, or using mm for one height and cm for the other.
• For black bodies, forgetting that a good absorber is also a good emitter.
• For Required practical 10, not keeping the detector the same distance from each face.

Official syllabus

AQA GCSE Physics (8463) specification, for first teaching 2016, exams from June 2018, version 1.1 (30 September 2019), published by AQA – section 4.6 Waves.