Investigating Planck's Constant with LEDs

This resource presents two hands-on lab activities that allow students to measure Planck’s constant for themselves. Both activities are based on simple electrical circuits involving LEDs. The first activity is a structured lab that includes a playdough circuit. The second activity is an open-ended, guided inquiry lab. 

Structured Inquiry 

Using a simple electrical circuit that involves a battery, an LED, some playdough, and two wires, students follow a series of instructions and measure a number of voltages. They then plot their data and use the slope of their line to calculate Planck’s constant — typically to within 20% of its actual value. 

Guided Inquiry 

This activity guides students to build a simple model for the energy in an LED. Next, they use the model to gather data and analyze it by plotting the data however they think is most appropriate. Finally, students are guided to use their plot to calculate Planck’s constant.