Pearson International A Level Physics Core Practical 5: Investigate factors affecting a vibrating string's frequency
Pearson IAL Physics practical notes on investigate factors affecting a vibrating string's frequency.
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
Test how resonant frequency depends on string length, tension or mass per unit length under controlled boundary conditions.
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 vibration generator, signal generator, string, pulley, masses, balance, metre rule and supports. 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
- Measure vibrating length and determine string mass per unit length from a long sample.
- Set tension using a known hanging mass and adjust frequency to a clearly defined fundamental or harmonic resonance.
- Change one factor at a time over at least five values and record repeat resonant frequencies.
- Linearise the predicted relationship, such as frequency against square root tension or reciprocal length.
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: length, tension or mass per unit length.
- Dependent variable: resonant frequency.
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