Experimental Determination of Planck’s Constant Using a Light Emitting Diode Method

Planck's constant is one of the most fundamental physical constants in quantum mechanics, and its experimental determination in undergraduate physics laboratories provides students with direct engagement with quantum theory. This study uses the threshold voltage method applied to light emitting diodes of different colors to experimentally determine Planck's constant in the Physics Laboratory of Nnamdi Azikiwe University, Awka, Anambra State, South East Nigeria. LEDs of six colors including red, orange, yellow, green, blue, and violet were sourced from local electronics suppliers. The forward bias threshold voltage of each LED was determined by finding the knee of the current-voltage characteristic curve using a variable power supply, digital voltmeter, and microammeter. The photon energy at threshold was calculated from the known peak emission wavelengths of each LED color, verified using a diffraction grating spectrometer. Planck's constant was derived from the slope of a photon energy versus frequency plot fitted by linear regression. The experimentally determined value of Planck's constant was 6.48 times 10 to the minus 34 J-s, representing a deviation of 2.2 percent from the accepted value of 6.626 times 10 to the minus 34 J-s. This level of accuracy was achieved with entirely locally sourced components costing less than 5,000 naira. The study concludes that LED-based Planck's constant determination is a practical, cost-effective, and motivating experimental approach for quantum physics teaching in Nigerian university laboratories. Keywords: Planck's constant, light emitting diode, quantum physics, undergraduate experiment, Nnamdi Azikiwe University