Is the You in the Mirror Real? A Hands-On Light Experiment on the Law of Reflection
I’m Ken Kuwako, a science trainer. Every day is an experiment.
You look at your face in the bathroom mirror in the morning. Scenery appears in a train window. The sky shows up in a puddle. Our everyday lives are full of reflected light. Yet if someone asks, “Why can we see objects in a mirror?” it is surprisingly hard to give a satisfying answer.
In this article, I’ll introduce a hands-on experiment that lets students explore the familiar yet fascinating law of reflection—not as a sentence in a textbook, but with their own eyes and hands.
Why Reflection Can Be Hard to Truly Feel
When teaching concepts such as the law of reflection and diffuse reflection, have you ever felt that textbook definitions alone do not quite connect with students? You can explain, “Light bounces off a mirror,” or “A rough surface scatters light in many directions,” but helping students reach that genuine “Now I get it!” moment is harder than it sounds. That is why it is so important to test these ideas through real experiments.
I have often wondered whether my students truly understood what they were seeing in an experiment. This activity is more than a way to deliver facts: it is a wonderful opportunity to sharpen observation skills and develop scientific thinking. When students see light’s curious behavior for themselves and work with it directly, their curiosity comes alive—and they can rediscover how exciting science can be.
Incidentally, the first known written record of the law of reflection is often attributed to the ancient Greek mathematician Euclid. As early as around 300 BCE, people already knew that the angle of incidence equals the angle of reflection. It is amazing to think that humans noticed the mystery inside a mirror more than 2,000 years ago.
What You’ll Need
- A light source (ideally one that produces parallel rays): A source that makes the beam easy to see is best. A laser pointer can also work, but choose carefully and keep beam spread in mind.
- A plane mirror: A hand mirror or a laboratory plane mirror will do. I recommend the card mirror sold at Daiso. It is inexpensive, easy to find, and lasts a long time.
- An observation sheet with a protractor (or a homemade version): This is essential for measuring the angles of incidence and reflection accurately. A large sheet of paper with angles marked using a protractor, plus a spot in the center for the mirror, is enough. This is the sheet I use: lines are drawn every 15 degrees, making it easy to see where to measure.
Procedure
Shine the light from the source onto the plane mirror, then measure and record the angles of incidence and reflection. The key is to focus students’ attention on measuring the reflected angle carefully. By making several measurements and confirming that the two angles are equal each time, students can arrive at their own insight into the law of reflection.
Using a card mirror
An Unexpected Offset with Card Mirrors
When you compare a card mirror with the mirrors sold by science education suppliers, you may find that at larger angles of incidence, the results sometimes differ from what the law of reflection predicts. This is what I observed when using equipment from Narika.
The reason is that card mirrors are coated with a thin layer of plastic to protect the reflective surface. As the angle of incidence increases, that coating can introduce a noticeable offset.
Light refracts once as it enters the transparent plastic layer and again as it leaves, bending its path slightly each time. At shallow angles, the difference is almost impossible to notice. But as the angle of incidence becomes larger, light travels farther through the layer, so the offset grows as well. That is exactly why careful observation and accurate recording matter.
For example, when these results are plotted on a graph, they look like this.
A discrepancy that is easy to miss in a table of numbers becomes obvious on a graph: “Oh—the difference appears only at the larger angles.” Teaching students not only to collect data but also to visualize it in a graph can be great practice for learning how to summarize a science experiment.
Next, let’s try an experiment on diffuse reflection.
Questions and Requests
Let’s bring the wonder and fun of science closer to everyday life! Here you’ll find enjoyable science experiments you can do at home, along with clear tips for making them work. Feel free to explore the site!
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