A-Level · Physics · AQA · Mark scheme decoded
AQA A-Level Physics: Waves: Oscillations and Properties — mark scheme explained
The short answer
In this section, we will explore the fundamental properties of waves, focusing on the oscillation of particles in a medium. We will delve into key concepts such as amplitude, frequency, wavelength, speed, phase, and phase difference.
The question
A sound wave has a frequency of 500 Hz and a wavelength of 0.68 m. Calculate the speed of the sound wave.
[Paraphrased for study — not reproduced from any exam paper.]
Mark scheme, decoded
How the examiner actually awards the marks on this topic.
Gradora's own decode of the marking approach — not the exam board's published mark scheme.
How marks are awarded
For calculation questions, marks are typically awarded for identifying correct formulas, substituting values correctly, and providing the final answer with appropriate units. For conceptual questions, marks are given for clear and accurate explanations.
What the command words demand
- Calculate
- Perform a numerical calculation using given data and appropriate formulas.
- Determine
- Find or measure a quantity, often through an experiment or graphical analysis.
- Explain
- Provide a clear and concise explanation of a concept or phenomenon.
- Describe
- Give a detailed account of the properties or behavior of a wave.
Model answer
A full-mark response to the question above, worked through step by step.
Timing: Allocate about 2-3 minutes per mark to ensure you have enough time to carefully read the question, perform calculations, and check your work.
- Identify the given values: f = 500 Hz, λ = 0.68 m.0 marks
- Use the formula for the speed of a wave: c = f × λ.1 mark
- Substitute the values into the formula: c = 500 × 0.68.1 mark
- Calculate the result: c = 340 m/s.2 marks
Final answer: 340 m/s
Work through every step correctly and you earn all 4 marks.
Another worked example
A wave has a period of 0.2 seconds and an amplitude of 0.5 meters. Calculate the frequency of the wave.
- Identify the given values: T = 0.2 s, A = 0.5 m (amplitude is not needed for this calculation).0 marks
- Use the formula for frequency: f = 1 / T.1 mark
- Substitute the value into the formula: f = 1 / 0.2.1 mark
- Calculate the result: f = 5 Hz.1 mark
Final answer: 5 Hz
Work through every step correctly and you earn all 3 marks.
Common mistakes
Confusing amplitude with frequency.
Why it happens: Students sometimes mix up the definitions of amplitude and frequency because both are related to wave properties. Amplitude is a measure of displacement, while frequency is a measure of oscillations per unit time.
Fix: Review the definitions: amplitude is the maximum displacement from equilibrium, and frequency is the number of cycles per second (Hz).
Using the wrong formula for speed of sound.
Why it happens: Students might use c = f + λ instead of c = f × λ, leading to incorrect calculations.
Fix: Memorize and practice using the correct formula: c = f × λ.
Forgetting to convert units when necessary.
Why it happens: Students often forget to ensure that all units are consistent before performing calculations, leading to incorrect results.
Fix: Always check and convert units to be consistent (e.g., meters for distance, seconds for time).
Misinterpreting phase difference as a physical distance.
Why it happens: Phase difference is an angle or fraction of a cycle, not a physical distance. Students might confuse it with wavelength or amplitude.
Fix: Understand that phase difference is a measure of the relative position in an oscillation cycle, expressed in radians, degrees, or fractions of a cycle.
Using the wrong formula for period (T).
Why it happens: Students might use T = f instead of T = 1 / f, leading to incorrect calculations.
Fix: Memorize and practice using the correct formula: T = 1 / f.
Incorrectly identifying the length of a tube in standing wave experiments.
Why it happens: In standing wave experiments, students might confuse the length of the tube with the wavelength. The length of the tube is related to half or a quarter of the wavelength depending on the boundary conditions.
Fix: Understand that for an open tube, L = λ / 2, and for a closed tube, L = λ / 4. Practice identifying the correct relationship based on the experiment setup.
Where the marks go
The question types you’ll meet on this topic and the marks each one carries — so you know what to expect and where to focus.
| Question type | What you’re asked to do | Marks |
|---|---|---|
| Calculate Wave Speed | Use the wave equation to find the speed of a sound wave from its frequency and wavelength. | 4 |
| Calculate Frequency | Use the period to calculate the frequency of a wave, giving correct units. | 3 |
| Calculate Wave Speed | Find the speed of a sound wave from its distance travelled and time taken. | 3 |
| Standing Wave Calculation | Find the wavelength and speed of sound in an open tube at fundamental resonance. | 6 |
| Total across these question types | 16 | |
Question types and mark tariffs are Gradora’s guidance based on how this topic is typically examined — not the board’s official paper structure.