Diffraction on a Budget

In physics class at Brock, we’re always talking about demonstrations that are good to do in front of a class that explain the concepts that are being discussed. The problem is, sometimes these demos require equipment that is hard to come by. The trick is, coming up with MacGyver alternatives that (sometimes) work just as well.

For example, the other day, Mark and I were talking about interference patterns created by light. (Sadly, this is a fairly typical Friday night for us.) After discussing this for a while, we took a look at what we had lying around the house and decided that we would make a diffraction pattern for ourselves.

What is a diffraction pattern, you may ask? Why, it’s just light interfering with other light, much like ripples on a pond interfere with each other and make overlapping patterns. We just capture these patterns from the light on a surface.

So, all you need is a business card (or other thick paper), a pin and a cheap laser pointer. Use the pin to poke two teeny tiny holes on the business card as close together as you can make them, and then shine the laser pointer through both the holes. (You might need to play around with the spacing of your holes before you can see anything.) You’ll need to stand about 20 feet from a wall and make sure that you’re in a dark room.

You should see this:

Diffraction Pattern

Ordinarily, the laser pointer would just create a red circle on the wall. But when you shine the laser pointer through the holes on the business card, the light (which travels like a wave) goes through ones of the holes, spreads out and interferes with the light spreading out from the other hole. These waves overlap – just like the waves-on-a-pond analogy. We’re just capturing that overlapping pattern on the surface of the wall, which ends up looking like a bunch of bright lines.

Pretty cool right? Science. It works.



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