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
What each mark is really for — in plain English — and the wording trap that loses it.
- S1
Identify the given values: f = 500 Hz, λ = 0.68 m.
- S2
Use the formula for the speed of a wave: c = f × λ.
- S3
Substitute the values into the formula: c = 500 × 0.68.
- S4
Calculate the result: c = 340 m/s.
Model answer
Worked through, with each step tagged to the mark it earns.
- S1
Identify the given values: f = 500 Hz, λ = 0.68 m.
- S2
Use the formula for the speed of a wave: c = f × λ.
- S3
Substitute the values into the formula: c = 500 × 0.68.
- S4
Calculate the result: c = 340 m/s.
Final answer: 340 m/s
Common mistakes
- Confusing amplitude with frequency. — 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. — Memorize and practice using the correct formula: c = f × λ.
- Forgetting to convert units when necessary. — Always check and convert units to be consistent (e.g., meters for distance, seconds for time).
- Misinterpreting phase difference as a physical distance. — 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). — Memorize and practice using the correct formula: T = 1 / f.
- Incorrectly identifying the length of a tube in standing wave experiments. — 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
- Full worked solution (all marking points)4 marks