Working Content > Three models of light > The photon model

Read the webpage the photon model. To get a sense of how this works, open the PhET simulation, Molecules and Light, and carry out a few tasks. When the program comes up, it is set to show you the result of infrared photons (wavelength ~1000 nm) incident on a carbon monoxide molecule.

1. Set the beam strength to on but low. Your screen should look like the image at the right. When you start the beam by pressing the run button, you should be able to watch photons one at a time. Watch for a while. What are the possibilities of what happens to the molecule when a photon goes by?

2. Now switch the beam to microwave (wavelength ~ 1 m). Now describe what happens. Why do you think there is a difference between what happens with microwaves and infrared light? What happens if you change to ultraviolet light (wavelength ~10 nm)?

3. Now change the molecule to nitrogen dioxide (NO₂) and explore what happens with microwaves, infrared, and ultraviolet light. Explain why the differences are happening and any differences between what you saw with CO.

Joe Redish 4/14/18