Diffraction happens when light goes around obstacles in its path. Sound waves diffract bend around obstacles, so if you’re stuck behind a pillar at a concert, you can still hear just fine.
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Ever play with a prism? When sunlight strikes the prism, it gets split into a rainbow of colors. Prisms un-mix the light into its different wavelengths (which you see as different colors). Diffraction gratings are tiny prisms stacked together.
When light passes through a diffraction grating, it splits (diffracts) the light into several beams traveling at different directions. If you’ve ever seen the ‘iridescence’ of a soap bubble, an insect shell, or on a pearl, you’ve seen nature’s diffraction gratings.
Scientist use these things to split incoming light so they can figure out what fuels a distant star is burning. When hydrogen burns, it gives off light, but not in all the colors of the rainbow, only very specific colors in red and blue. It’s like hydrogen’s own personal fingerprint, or light signature.
Astronomers can split incoming light from a star using a spectrometer (you can build your own here) to figure out what the star is burning by matching up the different light signatures.
Materials:
- feather
- old CD or DVD
Here’s what you do: Take a feather and put it over an eye. Stare at a light bulb or a lit candle. You should see two or three flames and a rainbow X. Shine a flashlight on a CD and watch for rainbows. (Hint – the tiny “hairs” on the feather are acting like tiny prisms… take your homemade microscope to look at more of the feather in greater detail and see the tiny prisms for yourself!
What happens when you aim a laser through a diffraction grating? Here’s what you do:
Materials:
- laser pointer
- diffraction grating (you can use an old CD also)
Download Student Worksheet & Excercises
Exercises
- Which light source gave the most interesting results?
- What happens when you aim a laser beam through the diffraction grating?
- How is a CD different and the same as a diffraction grating?
- Why does the feather work?