Pearson International A Level Physics Core Practical 4: Determine the speed of sound using an oscilloscope

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Measure a propagation delay or phase relationship over a known path length to determine sound speed.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use signal generator, loudspeaker, two microphones, oscilloscope, metre rule and stands. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Set a stable audible frequency and display microphone signals on separate oscilloscope channels.
2. Move one microphone through a measured distance between repeated in-phase positions or measure time delay over a larger path.
3. Repeat over several wavelength intervals to reduce fractional distance uncertainty.
4. Use speed = frequency times wavelength or distance divided by delay and compare repeats.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: microphone separation or signal frequency.
• Dependent variable: phase alignment distance or time delay.
• Important controls: