Modern Physics — Investigation · Physics & Environmental Science, Grade 12
Compare wave–particle evidence, relativistic limits, and nuclear mass-energy accounting.
Photoelectric Model from Data
Investigate
Does maximum electron energy depend on photon energy or brightness?
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
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
Fix the model surface work function at 2 eV. Vary photon energy and intensity separately.
Method
- Write a prediction and the mechanism that supports it.
- Draw the setup or boundary; label axes, quantities, and units.
- Predict threshold and maximum electron energy before examining data.
- Graph maximum energy against photon energy for emitting cases.
- Compare equal photon energy at different intensities and identify the simple model’s limits.
- 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.
| Photonenergy (e V) | Relativeintensity | Kmax (e V) | Emission? |
|---|---|---|---|
| 1.5 | 10 | 0 | No |
| 3 | 1 | 1 | Yes |
| 3 | 4 | 1 | Yes;moreelectrons |
| 4 | 1 | 2 | Yes |
Analyze and explain
- Infer the work function.
- Explain bright light below threshold.
- What changes when above-threshold intensity increases?
- 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
The work function is 2 eV. Above threshold Kmax=Ephoton−2 eV; a 1.5 eV photon lacks sufficient energy. Higher intensity at 3 eV gives more electrons but the same maximum energy. Multiphoton regimes are outside this model. 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.