CENCO® AP Physics Lab 24: Planck's Constant

Discover How an LED Works

Introducing the new Cenco AP Physics lab series. Ideal for AP, B and C, I and II, and advanced honors physics courses, each of the 24 experiments is aligned with the College Board AP Curriculum. The teacher guides and student manuals are authored by an experienced AP Physics teacher, so you can trust the setups to be successful in your classroom. Lead students through these hands-on labs using the outlined guided-inquiry approach. All labs come complete with instructions and materials for up to six students per lab group, the inquiry based instructions are found in the separate manuals. For your convenience, labs are packaged to allow you to purchase only what is required for each experiment.

Students will measure the wavelength and threshold voltage of an LED and then use these values to calculate Planck’s constant. How an LED works and how it can determine Planck’s constant is also demonstrated. The main apparatus has seven LEDs that are powered separately with a 9V power supply and a potentiometer. Students adjust the resistance until the current reads zero and then measure the voltage across the LED. Using the different stopping potentials and the wavelength of each LED, students can plot a graph from which Planck’s constant can be determined. The kit includes a Planck’s constant apparatus, wires, diffraction grating and two multimeters. Required but not included is a 9 V DC power supply or a 9V battery.

Note: AP and the Advanced Placement Program are registered trademarks of the College Entrance Examination Board, which was not involved in the production of and does not endorse these products.