Make a captivating moving artwork by illuminating a thick, clear liquid with a cell phone flashlight. The brilliant light patterns you create are called caustics and are found everywhere from the bottoms of swimming pools to the warping of light from distant galaxies.
- A clear, flat-sided bottle, such as a square-shaped plastic water bottle or a cell culture flask
- A clear, viscous liquid such as clear dish soap, heavy mineral oil, light corn syrup, or glycerin
- A point-source flashlight, like the kind found on most cell phones
- White paper, to act as a screen (not shown)
- A darkened room
To make the drip chamber, pour some of your chosen viscous liquid into the bottle or flask. Pour in just enough liquid that when the chamber is laid flat, the liquid forms a layer no more than a few millimeters thick.
Turn on your flashlight and go into a dark room, and place a piece of white paper on a table. Hold the drip chamber 6 to 12 inches (15 to 30 cm) above the paper and hold the flashlight about 4 inches (10 cm or more) above the drip chamber, pointing down. (Click to enlarge first photo below.)
Now, quickly turn your drip chamber over so the “floor” of the chamber becomes the “ceiling.” As the light shines through the chamber, watch the show on your paper screen as the drips ooze down. (Click to enlarge second photo.) Cool, right?
The light patterns you see on the paper screen are created by the bending of light, called refraction, as it passes through the rounded shapes of the clear liquid. Like a lens, a curved liquid surface can either concentrate or spread out light, causing brighter and darker regions to appear on the paper. These patterns of light are called caustics. Since the liquid is, well, liquid, it flows and changes shape, causing the caustic pattern to constantly change.
You can find caustics in plenty of places. A marble or a glass of water on a sunny window sill will make handsome caustics. Dazzling networks of caustics are a familiar sight on the bottoms of swimming pools. Older window glass, faintly rippled, can create caustics on walls and floors. Meanwhile, on a larger scale, the bending of light by gravity causes caustic patterns in the light from distant stars and galaxies.
Look around—what other caustics can you find?
Try to match one of the patterns you see on the paper with the convex or concave shape of the liquid inside the drip chamber.
Do you notice 120-degree angles and hexagonal shapes forming? Hexagons (and their characteristic 120-degree angles) are the most efficient geometry for dividing up a flat plane, and may appear spontaneously on the “ceiling” of your chamber. (Click to enlarge photo below.)
You can use this type of phenomenon to determine the relative sugar content of beverages, such as wine or juice. Swirling a glass of wine and then allowing the illuminated liquid to run down the sides of the glass produces caustic patterns. The speed of the changing patterns are an indicator of your drink’s sugar content. These drips of wine are known as “tears” and this type of patterning is known as “legs.” (Click to enlarge photo below.)
This Science Snack is part of a collection that showcases LGBT artists, scientists, inventors and thinkers whose work aids or expands our understanding of the phenomena explored in each Snack.
Dr. Chanda Prescod-Weinstein (she/her, pictured above) is an assistant professor of physics and core faculty member in women’s studies at the University of New Hampshire. As a theoretical researcher, she uses her knowledge and experience to contribute to our collective understanding of cosmology, particle cosmology, particle physics, and particle astrophysics. Her current research studies the hypothetical axion, a candidate for dark matter. The Drip Chamber Science Snack lets you visualize the interaction of light with various media, which mimics the phenomena of gravitational lensing caused by dark matter clusters and baryonic matter (“regular” matter) found in galaxies.
This lesson isn’t just great for introducing simple and complex concepts about light—it’s also beautiful.
Begin this activity with students arranged in groups at lab stations, each with a drip chamber and white paper on the table top. Before darkening the room, show students how to position the flashlight (phone), chamber, and paper, and ask them to predict what they’ll see.
After witnessing the effects caused by the drip chamber, have students discuss or record their observations. Ask whether they have questions, and what they want to try next.
Students may want to know what will happen if they:
- Change the height of the flashlight or drip chamber
- Add more fluid
- Use a different fluid
- Tilt the chamber
Let them experiment while carefully recording their results. These observations can relate to core scientific concepts as well as Science and Engineering Practices.
Students do not have to have any background knowledge to begin investigating the phenomena seen in this Snack. However, concepts ranging from basic to advanced can be incorporated, from patterns and prediction to how transparent drips cause these optical effects to more advanced topics like ray diagrams and refraction.
This Snack is great for use with young children, as well. They can safely experiment and investigate this phenomena as a whole class or in small groups. This Snack makes a great introduction to transparent media and pattern generation.
This Snack makes a good writing prompt for students, allowing them to practice describing what they see.