Marbles Are High-Performance Lenses! Discover How Light and the Eye Really Work with a Simple Marble
I’m Ken Kuwako, your Science Trainer. Every day is an experiment!
The Marble Lens Experiment
All you need for this experiment is a clear, transparent marble (one per person is best). In school settings, I buy them in bulk for students. The fact that it’s so inexpensive is part of what makes this experiment great!
Experiment 1: Focusing Light to Create a “Real Image”
First, place the marble on a white piece of paper and then lift it up just slightly. If you do this under a bright light source, like a fluorescent ceiling fixture, you’ll find a spot where the light passing through the marble is projected onto the paper.
It’s a little hard to tell from this photo, but the fluorescent light is projected onto the paper.
While it was tricky to photograph, if you look closely with your eye, you can clearly see the shape of the light fixture floating on the paper. This is what we call a real image. Because the marble is a sphere, it acts like a very powerful convex lens. By concentrating the light to a single point, it brings the image of the distant light fixture into focus on the paper. This is the exact same principle that allows our eyes and cameras to capture images.
Experiment 2: The Magnifying Glass Effect
Next, press the marble flat onto some printed text. This time, the marble transforms into a magnifying glass (or loupe).
Look at that! The character dai (大) is magnified about four times! When we view an object up close through a lens, we see what is called a virtual image, which is an enlarged version of the object. Reading glasses and microscopes use this very same property.
Experiment 3: The World Turns Upside Down – The “Inverted Real Image”
Finally, slowly lift the marble straight up, keeping it over the text. The moment you cross a certain height, something strange happens.
Did you notice? The text is now flipped both vertically and horizontally! The letter “F” in the image is completely inverted. When the lens (the marble) is moved a certain distance away from the object, the light rays cross paths, causing the image to appear flipped.
In fact, the images projected onto the retina in our own eyes are naturally upside-down as well. Our brain instantly corrects this, which is why we perceive the world as upright. It’s amazing that a single marble can demonstrate the mechanics of the human eye! When I hand these out to students, they all get engrossed in peering through them and playing. I truly believe that this kind of “play” is the doorway to an interest in science. Marbles are affordable when bought in bulk, so please try this out in your classrooms or at home!
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