How do Mirrors Work? The Science Behind Reflection
Since the earliest mirrors, which were disks of polished metal used in ancient times, people have marveled at the miracle of mirror reflection. While some thought it was magic, others already knew how mirrors work: it is pure physics. Optics, more precisely.
We thoroughly explain how mirrors work by discussing the two main questions:
- Why do mirrors reflect images?
- Why do mirrors reverse the image?
We will also touch upon the topics of curved mirrors and one-way mirrors. Let’s go!
Recall that a mirror is typically a sheet of glass backed by a thin metallic layer, often silver or aluminum. When light hits a mirror, most of it passes through the glass, strikes the reflective coating, and returns toward the viewer at an angle equal to that of the incoming light.
For this to work, however, the mirror’s surface must be extremely smooth so that the light rays bounce off in an orderly fashion, which in scientific language is called specular reflection.
When light rays hit a rough surface and bounce off in many directions, we call it diffuse reflection. That’s why objects like a snowman, though highly reflective, do not act as mirrors. All wavelengths of light are reflected, but they are so scattered that no mirror reflection can form.
Mirrors don’t truly reverse left and right; they actually reverse front and back, meaning the direction perpendicular to the mirror’s surface is flipped, much like pressing a stamp onto paper. When a mirror is mounted vertically on a wall, this front-back reversal makes our left and right appear swapped because we unconsciously imagine rotating around our vertical axis to face the reflection.
But if a mirror lies flat on a table, the same front-back reversal now acts along the vertical axis, making the image appear flipped up and down, similar to reflections seen on the surface of water. Try this experiment yourself; it really helps understand how mirrors work!
🙋 You can develop better intuition about why mirrors reverse images by playing with mirror writing. To see a quick example, check Omni’s mirror text generator or go to our dedicated article on the art of mirror writing.
Now that we understand why mirrors reflect images, it is time to dive deeper! In plane mirrors (those with flat reflective surfaces), images are the same size as the object. But curved mirrors can alter the size of an object! We distinguish two main types:
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Concave mirrors
They curve inward, converging light to a focal point. As a result, depending on distance, images can be magnified or inverted. Such mirrors are ideal for shaving, makeup, or burning hostile ships (as Archimedes allegedly did).
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Convex mirrors
They curve outward, spreading light rays and creating smaller images that show a wider field of view. This property is used in vehicle rearview mirrors as well as safety mirrors in stores and corridors, with the familiar warning that objects are closer than they appear.
Mirrors are placed in space to collect and focus faint light from distant stars, allowing astronomers to unravel the mysteries of our universe. For example, the James Webb Space Telescope utilizes a 6.5-meter mirror composed of 18 gold-coated hexagonal segments to capture more light than any previous space telescope, enabling us to marvel at the birth of stars.
Both terms refer to the same type of mirror: a sheet of glass coated with a thin, lightly reflective layer. If one side is brightly lit and the other remains in the dark, people on the bright side see their mirror reflection, while those on the dark side can see through. These mirrors are used in observation, interrogation, and security settings for discreet monitoring.
The difference in terms is mainly perspective:
- One-way mirror emphasizes the effect: mirror on the bright side, window on the dark side;
- Two-way mirror emphasizes the construction, which both reflects and transmits light.
Yes, mirrors can reflect a laser as long as the surface is smooth and reflective enough for the laser’s wavelength. However, if the laser beam is very strong, it can damage or even burn the mirror, so high-power lasers require special mirrors that are made of materials that can withstand intense energy.
This article was written by Anna Szczepanek and reviewed by Steven Wooding.