A curvy activity from Science Buddies
Key Concepts Physics Optics Light Reflection Cylindrical Glasses
Introduction Have you ever visited a house of mirrors and seen a wacky-looking version of yourself? In this activity you can construct your own miniature house of mirrors. Try it out and see what funny reflections you can make!
Background We see an object when light reflected from the object shines into our eyes. From that input of light, the brain uses the eyes' signals to reconstruct a picture of the object.
The brain makes a few assumptions in this process of reconstructing a picture. One assumption is that the light rays traveled in a straight line from the object to the eye. Although a light ray usually travels in a straight line, in some cases it can change direction first—for example, when a light ray enters or leaves a transparent material, such as water, or bounces off a shiny material, such as a mirror. Your brain still runs the usual reconstruction process, treating the image as if it were created by rays that travelled in a straight line. As a result, your brain might reconstruct a picture that looks different than the original object; your brain might have been fooled!
Light reflecting off of a surface is kind of like a ball bouncing on a floor. If the floor is flat and you drop the ball straight down, the ball will hit the floor and reverse direction, bouncing straight up. This direction is called "the normal" to the surface. If you drop the ball at an angle to this normal, it will bounce back at the other side of the normal, but with the same angle to the normal. The same principle applies to light reflecting (or bouncing back) from a surface. In this case, the ray of light approaching the surface is known as "the incident ray." If the incident ray strikes the reflective surface at a particular angle, the reflected ray leaves the surface at the same angle—but is located at the other side of the normal. In other words, the incident and reflected ray make a perfectly symmetrical V shape, with the normal as the line of symmetry.
Mirrors reflect almost all of the light hitting their surface. In addition, they have a very smooth surface and are usually flat, causing light to reflect in an orderly way, reflecting a good but "mirror image" of objects. This results in a neat image on the retina and thus a clearly reconstructed picture. Shiny surfaces that are not perfectly smooth can lead to blurry or fuzzy pictures.
Mirrors make it possible to see a picture of yourself or of objects that are behind you. But do they always give an accurate representation of how you or the objects behind you look? Try the activity to see how mirrors can fool you!
Observations and Results Did you see distorted reflections in the curved mirrors? Light rays that shine off a point on an object travel in all directions. Those reaching the mirror bounce back like a ball would bounce on a smooth surface. Some will travel into the eye. The location where these reflected light rays or their extensions meet is where the brain thinks the object is, so that is where the object appears to be when you see it in the mirror.
For the flat mirror, the skewers, which represent the normal to the surface, are parallel to each other. This creates reflected rays that meet at a point behind the mirror so the image appears at the other side of the mirror. For a flat mirror, the reflection is the same size and appears at the same distance from the mirror as the actual object.
For a convex mirror the skewers pointed outward. In this case light rays bounce the same way with respect to the normal but because the skewers point away from each other, the rays seem to spread out more compared to the ones reflecting on a flat mirror. These rays also meet at a point behind the mirror, but not as far behind it as the flat mirror. An object reflected in a convex mirror appears closer to the mirror and smaller than it really is.
For a concave mirror the skewers point toward each other, and the reflected light rays spread out less. The reflection of an object close to the mirror is bigger and looks farther away. If the skewers were long enough, they would have met at a point before the mirror. Move the object closer to the point where the skewers meet, and the reflected rays will spread out less. As a result the object will seem bigger and farther away. The reflection gets so big that your mirror probably only covers a fraction of it. Once you cross the point where the skewers meet, something strange happens: you see the object inverted! The right and left sides (if your mirror is in landscape orientation) or top and bottom (if you hold the mirror in portrait orientation) of the image are switched! This happens because the light rays meet before the mirror, so a light ray that starts at the right or the top will reflect back toward the left or the bottom. The inside of the spoon is curved in the horizontal and vertical direction, so right and left sides and top and bottom of the image are switched.
More to Explore The Reflection of Light, from Optics 4 Kids Concave Mirror—Why Is Your Reflection Upside Down on a Spoon?, from It's AumSum Time Why Is a Convex Mirror Used as a Rear View Mirror?, from It's AumSum Time Can You Create an Infinite Number of Reflections?, from Scientific American Use a Drop of Water as a Magnifying Glass, from Science Buddies Sight-Line Science: Candle in the Mirror, from Scientific American STEM Activities for Kids, from Science Buddies
This activity brought to you in partnership with Science Buddies
John Fialka and E&E News
Mariana Lenharo and Nature magazine
Daniel Cohan and The Conversation US
Alexandra Witze and Nature magazine
Discover world-changing science. Explore our digital archive back to 1845, including articles by more than 150 Nobel Prize winners.
© 2023 Scientific American, a Division of Springer Nature America, Inc.
Thanks for reading Scientific American. Knowledge awaits.
Already a subscriber? Sign in.
Thanks for reading Scientific American. Create your free account or Sign in to continue.
Continue reading with a Scientific American subscription.
Plano Concave Lenses You may cancel at any time.