Measuring Planck's Constant with LED Thresholds for H2 Physics Practicals

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 gives h/e; when multiplied by the electronic charge it delivers Planck's constant within 5 %.
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 Cambridge and SEAB examiners highlight in recent examiner reports.

Apparatus Checklist