The famous ancient Greek mathematician Archimedes reportedly used large concave mirrors during the war with Rome. By arranging six large concave mirrors in a circular pattern, he focused sunlight onto Roman ships, setting them on fire and securing victory. This is an example of using the principles of mirrors in warfare. It’s the same principle we used as children to focus sunlight through a magnifying glass to burn paper or leaves. Mirrors acted as a light-concentrating weapon.
We can see objects because of light. Objects that do not emit their own light reflect light from sources like the sun or lamps. This reflected light enters our eyes, allowing us to perceive the objects.
Mirrors are tools that reflect light to show the appearance of objects. They are made by coating the back of a flat glass surface with mercury and then painting it to prevent moisture. The reason objects are reflected in mirrors is that light travels in a straight line, hits the object, then reflects off the mirror into our eyes. Plane mirrors show the appearance of objects as they are.
The surface of a mirror is flat and smooth, reflecting all light at a consistent angle. Therefore, when we look at our face in a plane mirror, it appears exactly as it is, except for a left-right reversal..
Besides plane mirrors, we use curved mirrors in our daily lives. Curved mirrors can be concave or convex. The inside of a spoon acts as a concave mirror, and the outside acts as a convex mirror. Generally, concave mirrors gather reflected light, while convex mirrors disperse it.
When lighting the torch for the National Sports Festival at Manisan in Ganghwa Island using sunlight, a concave mirror is used to focus the light.
Concave mirrors are used in car headlights, lighthouses, and searchlights for safety purposes because they can gather light to project it brightly and far. The concave mirrors used for these purposes are parabolic rather than spherical to focus parallel light beams at a point and direct most light from the focal point parallelly to reach far distances. Placing the light at the focus of a parabolic mirror results in light reflecting parallel to the axis.
In car headlights, placing the bulb at the focus allows light to be projected far in the direction parallel to the axis. This is known as high beam. To avoid blinding oncoming cars, low beams are used, achieved by moving the bulb away from the focus. The light then spreads up and down, with the upward light blocked, so it only illuminates a short distance ahead.
Lighthouses operate similarly. They are not designed to brightly illuminate the surrounding sea but to mark dangerous areas like reefs with strong light. Scattered light could confuse sailors navigating in the dark. The basic purpose of a lighthouse is to ‘indicate.’ Ships rely on lighthouse beams to avoid hazards in pitch-black conditions.
Lighthouses use a lighting device called a lantern, surrounded by plane lenses to make the light parallel.
In contrast to concave mirrors, convex mirrors show a reduced, upright image regardless of the object’s position. The light reflected from a convex mirror reaches the eyes, with the curvature causing the light to converge more closely than from a flat surface. This makes objects appear smaller but allows a wider field of view, ensuring broader visibility.
Convex mirrors are used to see wide areas, such as in car side mirrors, at blind spots on accident-prone road corners, and in convenience stores or department stores to monitor blind spots. They are indispensable in convenience stores plagued by shoplifters.
Convex mirrors are also ideal for children’s rooms. A convex mirror in a corner allows a mother to see a child playing in a corner even from outside the room. Installing a convex mirror at an angle next to a baby’s crib is a good idea too, allowing constant monitoring from a distance without needing to check the crib closely.
Thus, convex and concave mirrors are tools that enhance our safety. Paying close attention to how mirrors work in our daily lives and acting accordingly can help prevent accidents.