You can measure this basic quantum constant using LEDs.
(Often, physicists like to be cool. Most of the time, we use the Greek letter ν (it’s not v) for frequency. It’s more complicated to write it that way.)
With this relationship between wavelength and frequency, we get this converted energy equation:
It turns out that it is easier to think of wavelength interactions than light and matter interactions.
Well, all of this was just a setup for an experimental method to determine Planck’s permanent value. The basic idea here is to use the colors of a bright LED to show the energy wavelength relationship. If I look for the amount of energy required to produce light as well as the wavelength of light (in other words color) I can determine h.
Here are some tips to help you get started:
Energy and LED
LEDs are everywhere. The LED flashlight and the new light bulb in your home are both LEDs on your smartphone. The red light in front of your television – it’s an LED. Even your remote uses an LED (although it is an infrared). LEDs come in different colors. You can easily find red, yellow, green, blue, purple, and more.
An LED is a semiconductor device with a difference in energy, often called a band gap. When an LED is connected to a circuit, it starts the flow of electrons. The difference in energy is similar to the transfer of energy in a hydrogen atom. Electron bands may be present on either side of the gap, but not in the middle. If an electron has the right energy, it can cross the band gap. And because the electron loses energy in the jump, it produces light. The wavelength, or color, of this light depends on the size of the band gap.
Nothing happens if you connect the LED to a 1.5 volt voltage from a D battery. To brighten the LED you need to increase the voltage to a certain value – this is called forward. Red LEDs typically require 1.8 volts and blue LEDs require 3.2 volts.
Let’s actually measure that value. Here is my experimental setup. I have a variable power supply from LED. I can slowly increase the voltage and measure the electric current. Only when the current starts to increase will you be able to see the visible light.