Measuring Planck's Constant with LED Thresholds for H2 Physics Practicals
Study guide
Q: What does Measuring Planck's Constant with LED Thresholds for H2 Physics Practicals cover?
A: Build a repeatable LED threshold experiment that nails Planck's constant within exam tolerances, reinforces quantum concepts.
TL;DR
Use a string of different coloured LEDs, a variable power supply, and spreadsheet regression to plot photon energy against frequency.
The intercept of the best-fit line givesh/e; when multiplied by the electronic charge it often lands close to the accepted Planck constant if uncertainties and controls are handled carefully.
Bake in calibration checks, dark-room controls, and full uncertainty paragraphs to turn a simple demo into a top-tier Paper 4 investigation.
Why This Experiment Hits the 9478 Syllabus
H2 Physics candidates must demonstrate mastery of quantum photoelectric ideas and linear data analysis. The LED threshold experiment ticks both boxes:
- Threshold voltage maps directly onto photon energy
E = hf, making the link between circuit measurements and quantum theory explicit. - The procedure mirrors SEAB Paper 4 expectations - control temperature, justify graphical methods, and estimate uncertainties on slope and intercept.
- Students rehearse digital acquisition workflows that align with Paper 4’s emphasis on spreadsheet analysis.
Apparatus Checklist
| Item | Notes |
| Assorted LEDs (violet to red) | Use at least five distinct peak wavelengths between 400 - 650 nm. |
| Variable DC supply (0 - 6 V) or USB-C PD trigger | Fine voltage control in 0.01 V steps lets you land exactly on the threshold. |
| Series resistor (1 kΩ) & breadboard | Limits current spikes that can damage LEDs. |
| Digital multimeter or Arduino DAQ | Log both voltage and current; ensure millivolt resolution. |
Reviewed by
Chee Wei Jie·Academic Advisor (Physics)
Practical course completion-record note
For practical, lab, and experiment courses, Eclat Institute maintains centre-held attendance records and may also issue an internal attendance or completion document based on participation and internal assessment.
- For SEAB private-candidate declarations, the key evidence is the centre's attendance or completion record, not a government-issued certificate.
- This is an internal centre-issued certificate, not an MOE/SEAB qualification or accreditation.
- Recognition (if any) is determined by the receiving school, institution, or employer.
- For SEAB private candidates taking science practical papers, SEAB states you should either have taken the subject before or attend a practical course and complete it before the practical paper date.
View our sample completion document (Current sample layout (design may be refined over time))
