Montshire Minute: Lenses

Originally aired during the week of September 24, 2001

Monday

How do lenses make objects look bigger or smaller? Lenses are made from materials that you can see through, like glass or plastic. One or both sides of the lens are curved. Rays of light are refracted causing the object beneath the lens to look larger or smaller. Refracting light means that light rays are bent when they pass through a lens. That's right, bent. Different types of lenses refract light in different ways. A concave lens is thick at the edges, and thin in the middle. Look through a concave lens, and objects will look smaller. A convex lens will make an object look bigger than it is. These types of lenses are thick in the middle, and thin on the edges. Glasses with convex lenses help people see better by making objects look bigger! Our new visiting exhibit called Experiment Gallery allows you to do all kinds of experiments with lenses.

Tuesday

We encounter lenses every day in life, from eye glasses to telescopes. But just how long have people known that we can bend light with lenses? The Greeks and Romans made the earliest lenses, which were basic glass spheres filled with water. True glass lenses were manufactured around the beginning of the 13th century in Europe. Lens making has not changed much since then. High quality glass is used because it is free of air bubbles and other imperfections. The glass goes through a process of shaping and polishing until a perfect lens is created. Development of plastics and special molding processes in recent times has led to an increased use of non-glass materials for lens making. Plastic lenses are lighter, cheaper, and not as fragile as glass ones.

Wednesday

If a smooth surface, flat or curved, is capable of reflecting most of the light that falls on it, it can be called a mirror. Mirrors are scarce in nature - most objects would absorb too much light to be good mirrors, even if they were comparatively smooth. Surfaces of objects in the natural world like dirt, stones, and leaves, are mostly irregular - they are made up of many tiny surfaces. Light rays bouncing off these surfaces scatter in many different directions, resulting in a diffused reflection. Ordinary household mirrors are made of plate glass coated on the back with an alloy - the glass serves only to shape the metal film and protect it. This "plane mirror" is the only optical device that's capable of forming a completely accurate image (although it appears to be in reverse) of an object.

Thursday

Looking for a quick weight loss solution? Take a goooood look in Montshire's anti-gravity mirror. This mirror can make it look as though you are actually floating in mid-air. How does it work? Light will always bounce off a mirror at the same angle that it hits. If you stand in front of a mirror slightly to one side, you'll see your image reflected slightly to the other side. The Anti-Gravity Mirror combines one side of your body and its mirror image together - an observer might momentarily be fooled into thinking it's you, but it's really only half you and your half's reflection. Hopefully your better half. Anyway, stand on your leg that's behind the mirror, lift your other leg up, and you'll appear to be hanging in mid-air, defying gravity. There are several other mirrors that are part of Monthsire's new touring exhibit The Experiment Gallery.

Friday

We've been learning about lenses all week on the Montshire Minute. Want to make your own? It's easy! Get a small piece of cardboard, or heavy paper. Carefully cut a round hole into the middle of the cardboard, about one inch in diameter. Stick a piece of clear plastic tape across the hole. Now use a straw to place a drop of water onto the tape. Then you can look at a newspaper, a leaf, or your hand through the drop of water. Notice how the object looks bigger? What you've made is a convex lens. Convex lenses bend light to make objects look bigger. Concave lenses make things look smaller. You can find out more about lenses and many other things here at the Montshire Museum. Our new exhibit, called Experiment Gallery, allows you to make all kinds of other experiments with lenses. The exhibit will be on display until January 13!