Polarization has to do with the direction of the light.  Think of a white picket fence – the kind that has space between each board.  The light can pass through the gaps int the fence but are blocked by the boards.  That’s exactly what a polarizer does.


When you have two polarizers, you can rotate one of the ‘fences’ a quarter turn so that virtually no light can get through – only little bits here and there where the gaps line up. Most of the way is blocked, though, which is what happens when you rotate the two pairs of sunglasses. Your sunglasses are polarizing filters, meaning that they only let light of a certain direction in. The view through the sunglasses is a bit dimmer, as less photons reach your eyeball.


Polarizing sunglasses also reduce darken the sky, which gives you more contrast between light and dark, sharpening the images. Photographers use polarizing filters to cut out glaring reflections.


Materials:


  • two pairs of polarized sunglasses
  • tape (the 3/4″ glossy clear kind works best – watch second video below)
  • window

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Here’s what you do: Stack two pairs of sunglasses on top of each other and look through both sets of lenses… now rotate one pair a quarter turn (90o).  The lenses should block the light completely at 90o and allow light to pass-through when aligned at 0o. These lenses allow some light to pass through but not all. When you rotate the lenses to 90o, you block out all visible light.


You use the “filter” principle in the kitchen. When you cook pasta, you use a filter (a strainer) to get the pasta out of the water. That’s what the sunglasses are doing – they are filtering out certain types of light. Rotating the lenses 90o to block out all light is like trying to strain your pasta with a mixing bowl. You don’t allow anything to pass through.


Astronomers use polarizing filters to look at the moon. Ever notice how bright the moon is during a full moon, and how dim it is near new moon? Using a rotating polarizing filter, astronomer can adjust the amount of light that enters into their eye.



 
Download Student Worksheet & Exercises


Advanced students: Download your Polarization lab here.


Exercises


  1. Why do you need two polarizers to block the light completely?
  2.  How can you tell if your sunglasses are polarized if you only have one pair?

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Comments

12 Responses to “The Dark and Light of Polarization”

  2. Cindy Soderlund says:

    I really like the polarized screens you use in your video. May I ask where I can get a pair? TIA!

  3. No, it means that your sunglasses are not polarized, and you’ll want to find a different pair to use.

  4. Caroline Wood says:

    what if when i rotate they don;t go black at all. will it still work?

  5. Laura Stephenson says:

    You spelled “when” wrong. I love it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    Hannah Age 10

    Your biggest fan 🙂 😉

  6. jenna6234 says:

    SWEET EXPIREMENT LOVE IT!!!

  7. Yes you’ll find this effect everywhere now – on digital watches, computer screens, and more!

  8. Lydia Fancher says:

    kinda like a 3-D tv! I think when you have the glasses on you turn your head 90 degrees and it goes black… or double vision :/ I don’t really remember exacly what it does…

  9. Actually, you need only one pair to do this experiment. Instead of a second pair, simply use your iPOD, digital watch, or other digital display to see this effect. Here’s what you do: look at the display of your iPOD with your sunglasses on. Rotate the iPOD 90 degrees – you should see the screen go dark. That’s because there’s a polarizing filter on the display!

  10. Do we really need two pairs of sunglasses to do this experiment?

  11. That’s ok – you just need to notice that one way they go black, and 90 degrees from that (a quarter turn) they are see-through again. It just means that your lenses in your sunglasses are not parallel (not put in the same way) – one set is rotated. Weird effect, isn’t it?

  12. sevy keble says:

    This is a very nice expirement, 🙂 but when we rotated the sunglasses, it didn’t go dark :(. Instead, :O it was black when we didn’t rotate it! :-P!
    Sevy keble