Waves: Exam Practice

This lesson brings together all the key topics from the AQA GCSE Physics Waves chapter (4.6) and provides structured exam practice with worked examples, common question types, and strategies for maximising your marks. Use this lesson to consolidate your knowledge and practise applying it under exam conditions.

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Key Equations to Remember

You must know these equations for the exam. Some are on the equation sheet; others must be memorised.

Equation	What It Links	On Equation Sheet?
v = f x lambda	Wave speed, frequency, wavelength	Yes
T = 1 / f	Period and frequency	Yes
v = s / t	Speed, distance, time	Yes

Using the Wave Equation

For every calculation question involving waves, follow these steps:

1. Write the equation.
2. Substitute the values (with correct units).
3. Calculate the answer.
4. State the answer with the correct unit.

Exam Tip: Even if you make an arithmetic error, you can still earn marks for writing the correct equation and substituting the values correctly. Always show your working — never just write the answer.

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Worked Example 1: Wave Speed Calculation

Question: A sound wave has a frequency of 256 Hz and a wavelength of 1.33 m. Calculate the speed of the sound wave.

Answer:

v = f x lambda

v = 256 x 1.33

v = 340.48 m/s

v = 340 m/s (to 3 significant figures)

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Worked Example 2: Frequency from Period

Question: A wave has a period of 0.005 s. Calculate the frequency of the wave.

Answer:

f = 1 / T

f = 1 / 0.005

f = 200 Hz

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Worked Example 3: Wavelength of an EM Wave

Question: A microwave oven operates at a frequency of 2.45 GHz. Calculate the wavelength of the microwaves. (Speed of EM waves = 3 x 10^8 m/s)

Answer:

First, convert GHz to Hz: 2.45 GHz = 2.45 x 10^9 Hz

lambda = v / f

lambda = (3 x 10^8) / (2.45 x 10^9)

lambda = 0.122 m

lambda = 0.122 m (or 12.2 cm)

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Worked Example 4: Echo Calculation

Question: A ship sends an ultrasound pulse towards the seabed. The echo returns after 0.08 s. The speed of sound in seawater is 1 500 m/s. Calculate the depth of the seabed.

Answer:

distance = (speed x time) / 2

distance = (1 500 x 0.08) / 2

distance = 120 / 2

distance = 60 m

Exam Tip: Always divide by 2 in echo questions because the sound travels to the reflector and back. Forgetting to halve the distance is one of the most common errors in wave calculations.

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Common Question Types

Type 1: Define and Compare Transverse and Longitudinal Waves

Model Answer (4 marks):

• In a transverse wave, the oscillations are perpendicular (at right angles) to the direction of energy transfer. Example: light.
• In a longitudinal wave, the oscillations are parallel to the direction of energy transfer. Example: sound.
• Both types transfer energy without transferring matter.
• Only transverse waves can be polarised.

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Type 2: Describe the Electromagnetic Spectrum

Model Answer (6 marks):

The electromagnetic spectrum is a continuous range of transverse waves, ordered by wavelength from longest to shortest: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.

All EM waves:

• Travel at the same speed in a vacuum (3 x 10^8 m/s).
• Are transverse waves.
• Can travel through a vacuum.

From radio waves to gamma rays:

• Wavelength decreases and frequency increases.
• Energy increases.
• UV, X-rays, and gamma rays are ionising and can damage cells and DNA.

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Type 3: Required Practical — Ripple Tank

Model Answer (6 marks):

To measure the speed of water waves:

1. Set up a ripple tank with a motor and dipper to produce regular waves.
2. Place a lamp above the tank to project wave shadows onto white paper below.
3. Use a stroboscope to freeze the wave pattern.
4. Measure the distance across several wavelengths (e.g. 10) using a ruler, then divide by the number of waves to find one wavelength.
5. Use a stopwatch to time a set number of waves passing a point, then calculate frequency: f = number of waves / time.
6. Calculate wave speed: v = f x lambda.
7. Repeat and calculate a mean to improve reliability.

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Type 4: Explain Refraction

Model Answer (4 marks):

Refraction occurs when a wave crosses a boundary between two media of different density. The wave changes speed, which causes it to change direction (unless it hits the boundary along the normal).

• When a wave enters a denser medium (e.g. air to glass), it slows down and bends towards the normal.
• When a wave enters a less dense medium (e.g. glass to air), it speeds up and bends away from the normal.
• The frequency stays the same; the wavelength and speed change.

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Type 5: Uses and Dangers of EM Waves

Model Answer (6 marks):

graph TD
    subgraph "Uses and Dangers"
        UV["Ultraviolet"] --> U1["Use: sterilisation of water and equipment"]
        UV --> D1["Danger: skin cancer, eye damage (cataracts)"]
        XR["X-rays"] --> U2["Use: medical imaging of bones"]
        XR --> D2["Danger: ionising - can cause DNA mutations and cancer"]
        GA["Gamma rays"] --> U3["Use: radiotherapy to treat cancer"]
        GA --> D3["Danger: highly ionising - cell damage and radiation sickness"]
    end
    style UV fill:#2980b9,color:#fff
    style XR fill:#8e44ad,color:#fff
    style GA fill:#2c3e50,color:#fff

UV radiation is used in fluorescent lamps and to sterilise equipment. However, UV is ionising and can cause skin cancer and cataracts. Protection includes sunscreen and UV-blocking sunglasses.

X-rays are used for medical imaging (broken bones, dental checks). They are ionising, so exposure is minimised. Radiographers stand behind lead screens, and patients wear lead aprons.

Gamma rays are used in radiotherapy to destroy cancer cells and to sterilise medical equipment. Workers use remote handling and wear film badges to monitor exposure.

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Type 6: Required Practical — Infrared Emission and Absorption

Model Answer (6 marks):

To investigate infrared emission, use a Leslie cube filled with boiling water. Place an infrared detector at a fixed distance from each surface (matt black, matt white, shiny black, shiny silver). The matt black surface gives the highest reading, showing it is the best emitter.

To investigate absorption, place a matt black and a shiny silver metal plate at equal distances from a radiant heater. Record the temperature rise over time. The matt black plate shows a greater temperature rise, proving it absorbs infrared more effectively.

Control variables: distance from heater/detector, starting temperature, room temperature, plate material and size.

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Exam Command Words

Command Word	What You Must Do
State	Give a brief, factual answer — no explanation needed
Define	Give the precise scientific meaning of a term
Describe	Say what happens, step by step or feature by feature
Explain	Say what happens AND why (give reasons using scientific knowledge)
Calculate	Show working, substitute values, give the answer with units
Compare	Give similarities AND differences between two things
Evaluate	Consider the evidence and make a judgement, discussing strengths and weaknesses
Suggest	Use your scientific knowledge to propose an answer — there may not be a single correct answer

Exam Tip: Always read the command word carefully. "Describe" does not require reasons — just say what happens. "Explain" requires you to give reasons using scientific principles. Missing the command word is one of the biggest reasons students lose marks.

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Tackling 6-Mark Questions

For extended response (6-mark) questions on waves, use this structure:

1. Introduction — state the key principle or definition.
2. Main body — give detailed scientific explanation with specific facts, equations, and examples.
3. Conclusion — summarise the key finding or answer the question directly.

Tips for 6-Mark Questions