This box shows Planck's Constant in action.

With LEDs in a range from 470-940nm, this innovative device allows students to approximate the value of h, Planck's constant. For each wavelength produced, you can record the threshold voltage.

• For Determining Approximate Value of Planck's Constant
• Seven LEDs from 470 nm to 940 nm
• Users Can Plot a Graph of Energy Input

This apparatus is designed to determine the approximate value of Planck's Constant using the elbow voltage in the characteristic curves of a number of LEDs. There are seven LEDs mounted on the box with sockets for voltage and current measurements. By monitoring the voltage at which each LED begins to emit light, users can plot a graph of energy input as a function of light emitted frequency and deduce an approximate value of Planck's Constant.

An external power supply for 9V is required. A 9V battery with suitable connecting cords can also be used.