Electronics · Semiconductor devices / Principles and inquiry
LED colors and the Planck constant experiment guide
Find and record the turn-on voltage for each LED color. Estimate the Planck constant from the slope of threshold voltage against frequency.
How does it work?
Higher-frequency LEDs have higher threshold voltages. Estimate h from the slope using several colors.
f = c/λ · eVth ≈ hf · h estimate = e × slope(Vth vs f)
Try this investigation
- Choose a color and adjust voltage in 0.01 V steps to find the turn-on boundary.
- For red, green and blue, use the threshold button or adjust voltage manually, then run and record.
- Record a calibration offset and two other colors, then compare the estimates.
Interpreting your results
If the V–f slope is 4.14×10⁻¹⁵ V·s, what estimate of h results from multiplying by e?
About 6.63×10⁻³⁴ J·s
Assumptions and limitations
This is an educational approximation eV ≈ hf. Real LED band gaps, contact voltages and turn-on criteria can cause larger errors. Noise is a reproducible fixed color correction. The threshold button helps locate the ideal model boundary. Use this simulation; do not reproduce it with real power supplies or wall outlets.