Did you know that you can use a laser to see tiny paramecia in pond water? We’re going to build a simple laser microscope that will shine through a single drop of water and project shadows on a wall or ceiling for us to study.


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Here’s how it works: by shining a laser though a drop of water, we can see the shadows of objects inside the water. It’s like playing shadow puppets, only we’re using a highly concentrated laser beam instead of a flashlight.


If you’re wondering how a narrow laser beam spreads out to cover a wall, it has to do with the shape of the water droplet. Water has surface tension, which makes the water want to curl into a ball shape. But because water’s heavy, the ball stretches a little. This makes the water a tear-drop shape, which makes it act like a convex lens, which magnifies the light and spreads it out:


Here’s how to make your own laser microscope:


Materials:


  • red or green laser (watch video for laser tips)
  • large paperclip
  • rubber band
  • stack of books
  • white wall
  • pond water sample (or make your own from a cup of water with dead grass that’s been sitting for a week on the windowsill)


Download Student Worksheet & Exercises


Exercises


  1. Does this work with other clear liquids?
  2.   What kind of lens occurs if you change the amount of surface tension by using soapy water instead?
  3.   Does the temperature of the water matter? What about a piece of ice?
  4.  Does this work with a flashlight instead of a laser?
  5.  Do lasers hurt your eyes? How?

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Comments

8 Responses to “Laser Microscope”

  1. Aurora Lipper says:

    Actually, the pond water is just held in place inside the little loop of a paperclip. The video shows how to bend the paperclip.

  2. Aurora, what was the container for the pond water when you projected it onto the wall? Did you have the pond water in a clear bottle and beam the green laser from the opposite side of the wall?

  3. Sure, just aim it at a blank white wall and move closer or further until it comes into focus, just like aiming a flashlight on the wall. Have fun!

  4. privatefortsao says:

    Aurora is it possible for you to tell me how you were able to project it onto the white wall? Thanks!

  5. Those are most likely tiny pieces of plant.

  6. What are the two long dark columns that go from a little bit above the cats head to the top/top right corner?

  7. Oh no! You’re right – the wrong one was inserted here. I’ll get the right one up for you right away. Thanks for catching that – we’ve been replacing all the videos with new video players, so thanks for your eagle eye!

  8. Is the current video correct? Because it shows nothing about a laser but it just shows the magnifying glass microscope.