Waves, Sound & Optics — Investigation · Physics & Environmental Science, Grade 12
Connect wave patterns, sound, electromagnetic radiation, interference, and refraction.
Standing-Wave Patterns
Investigate
Do node measurements predict wave speed?
Use two dedicated sessions: first define the model, boundary, variables and comparison, then collect suitable records or analyze the complete supplied-data route; second complete calculations/graphs, compare alternatives, revise and prepare the report. Extend collection time where needed. Supplied-data work does not certify supervised laboratory minutes or mandated investigations.
Materials
- Notebook, graph paper, and calculator
- The supplied data table is sufficient for analysis
- Optional household setup described in the method; an adult checks safety
Before you begin
Use only the listed household materials or analyze the supplied data. An adult should review setup. No flames, strong acids/alkalis, unknown chemicals, household mains, radiation sources, or high-speed projectiles are needed. Keep food-study materials separate from eating and wash hands afterward.
Plan a fair test
Use a fixed model string length of 1.2 m and constant wave speed while comparing harmonics.
Method
- Write a prediction and the mechanism that supports it.
- Draw the setup or boundary; label axes, quantities, and units.
- Draw fixed-end modes with one, two, and three antinodes.
- Measure or use node spacing to infer wavelength.
- Multiply frequency by wavelength for each mode and compare speed estimates.
- Record independent repetitions where possible, raw values, and instrument resolution.
- Write a claim citing numerical evidence, a limitation, and a follow-up test.
Example data — for analysis when materials are unavailable
Illustrative teaching data, not measurements from a real district laboratory. Analyze these when materials are unavailable and identify them as provided data. Do not claim to have performed a measurement you did not make.
| Mode | Frequency (Hz) | Wavelength (m) |
|---|---|---|
| 1 | 20 | 2.4 |
| 2 | 40 | 1.2 |
| 3 | 60 | 0.8 |
Analyze and explain
- Find wave speed in every row.
- Find adjacent node spacing in mode 2.
- How can damping or changed tension affect observations?
- Link the pattern to a labeled particle, structure, energy or amount model from the chapter.
- Distinguish supplied illustrative records from measurements actually collected.
- Identify uncertainty and propose a comparison that would test an alternative explanation.
What a strong explanation includes
- A stated prediction, conditions, and controlled variables or explicit model boundary.
- A labeled table/graph with units, calculations, and attention to repeated values or uncertainty.
- A claim citing numerical evidence and a scientifically accurate mechanism.
- A limitation, alternative explanation, and useful follow-up test.
- Preserve initial reasoning and an evidence-supported revision.
- Check units, object/material identity, system boundary and physical assumptions.
Parent / teacher guide: discuss after the investigation
Every row gives 48 m/s. Mode 2 has nodes 0.60 m apart. Fixed boundaries determine the allowed patterns; damping limits amplitude, and changes in tension can change the speed. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.