You Can Measure This Standard Frequent Quantum Using LEDs
(Usually, physicists like to be cool. Usually, we use the Greek letter ν (it’s not v) for the most part. It’s more sophisticated to write it that way.)
With this connection between wavelength and frequency, we obtain this modified energy equation:
Now it is much simpler to think of the relationship between light and matter in terms of wavelengths than frequency.
OK, all this is just a setup for an experimental method to determine the value of the Planck constant. The basic idea here is to use the colors of an illuminated LED to show this relationship of energy to longitude. If I could find the amount of energy needed to produce the light, as well as the length of the wavelength (in other words, the color) of the light produced, I would know h.
There are a few little tricks involved – so let’s get to that.
Power and LEDs
LEDs are everywhere. That flashlight on your smartphone and that new bulb in your house are both LEDs. The red light on the front of your television – it’s an LED. Even your remote device has an LED (though it is an infrared). LEDs come in a variety of colors. You can easily find red, yellow, green, blue, violet, and more.
An LED is a semiconductor device with an energy gap, often referred to as a band gap. If the LED is connected to a circuit, it will start a flow of electrons. The energy gap is the same as the energy transfer of the hydrogen atom. Electrons can be present on either side of the band gap, but not in the middle of it. If an electron has the right energy, it can jump into the band gap. And because the electron loses energy to make the jump, it gives off light. The length of the wavelength, or color, of this light depends on the size of the band gap.
If you connect an LED to a D battery with a voltage of 1.5 volts, nothing happens. You need to increase the voltage by a certain amount to get the LED lit – this is called forward. Red LEDs typically require about 1.8 volts and blue ones require about 3.2 volts.
We will definitely measure this amount. Here is my prepared experiment. There is a variable power supply connected to an LED. I can slowly increase the voltage and measure the electrical current. When the temperature starts to rise, that’s when you see the visible light.