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    Home / Science lessons / The Camera & the Vacuum Cleaner
    • The Camera & the Vacuum Cleaner

      We are surrounded by inventions that make our lives easier. It is hard to imagine life without a vacuum cleaner, and we would all miss the ability to record our lives in photographs. These inventions and others are the results of many creative people, sometimes devoting their lives to a single project. Inventors require a lot of perseverance - Thomas Edison, for example, tried thousands of experiments before he perfected his light bulb design.


      In these days of disposable cameras, digital cameras, and camera phones, it is hard to imagine a time when people couldn't record their memories in color with the push of a button. Before 1888, photography was expensive and the necessary equipment cumbersome. But then George Eastman developed roll film and patented the first portable, hand-held Kodak camera. The camera came pre-loaded with film, and after taking 100 exposures the owner sent the entire camera to the Eastman Kodak Company, where the film was removed and developed. Kodak loaded new film into the camera and sent the pictures and camera back to the owner. In other words, Eastman's slogan, 'You Press the Button and We Do the Rest,' was very accurate!

      A camera can be a very complex machine with focusing mechanisms, flashes, and other features, but at its most basic it needs just three main elements:

      • Lens. Light is reflected off of an object in all different directions. A convex lens bends the light rays and focuses them so they converge in a single point. At that point, an upside-down, reversed 'real image' of the object is formed. (You can see how a lens focuses light by holding one over a piece of white paper in front of a window. The lens will focus the sunlight into a small bright beam on the paper.) To take a picture, a camera lens has to focus the light reflecting off the scene in front of it into a small area on a light-sensitive surface.
      • Light-sensitive material. In a camera, the lens focuses the light into a point on film. Film is treated with chemicals that undergo a chemical reaction when exposed to light, thus recording the image. Since it is light sensitive, the film has to be developed in a dark room. Developing involves several steps and different kinds of chemicals before you get a picture ready for your scrapbook.
      • Shutter. Since film is highly sensitive to light, it will be ruined if it is exposed to light too long. The shutter is the part of the camera between the lens and the film - it controls when and how long light can reach the film. When you take a picture, the shutter opens allowing light to hit the film, then closes almost immediately. How long the shutter stays open (exposure time) depends on how sensitive your film is and how much light there is. On bright sunny days, the shutter will need to stay open for much less time than at night.

      You may be wondering why the real image is upside-down and reversed. This is because light bouncing off the bottom of an object has to be bent upward by the lens, and light from the top has to be bent downward. They will cross, so when they make the image, it will be upside down. The same thing happens side to side, which is why the image is also reversed.

      The earliest type of camera was called a camera obscura, which is Latin for 'dark room.' It consisted of a dark room with a tiny hole for light to come through. The hole acted like a lens, because it only allowed light to enter as a single narrow beam; this beam produced a reversed image of outside objects on the wall opposite the hole. Since Aristotle mentions this type of camera in his writings, we know it was used to view the sun as early as 300 B.C.! Eventually the camera obscura was made out of a large box and had lenses to flip the image right side up. Historians believe that artists such as Johannes Vermeer used these to view an image of the scene they wished to paint.

      The camera obscura accomplished only half of what a modern camera does - it focused light reflecting off of objects into a single narrow beam that produced a real image of the objects. But this only produced the image; it didn't record it. It wasn't until the early 19th century that scientists developed light-sensitive plates that could receive the image. And the early methods weren't very efficient - photographic images were the result of 8 hours or more of exposure to light. Eventually a Frenchman named Daguerre invented the Daguerreotype - a process of photographing on metal plates. The exposure time was considerably shorter - about 10 to 20 minutes - but still long enough to explain why people didn't try to smile in those old photographs! Through the efforts of many different people, exposure time was reduced to a few seconds by the mid-1800s. When Eastman figured out how to roll the film so it could fit in a hand-held camera, photography became available to the masses, and cameras have been indispensable ever since!

      Camera technology continues to advance. Today's digital cameras do away with film altogether. The light is focused onto a semiconductor that records it electronically, instead of chemically like film does. Then the electronic impulses are converted into the 1s and 0s of computer language, producing an image made up of tiny colored dots, or pixels. These images can be easily changed, resized, e-mailed, or uploaded on websites.

      Click here to make your own camera obscura, also called a pinhole camera!

      Vacuum Cleaner

      Imagine wanting to vacuum your carpets in the early years of the 20th century. You would have to call a door-to-door vacuuming service, which would send a huge horse-drawn machine to your house. Hoses would be fed through your windows, attached to the gasoline-powered vacuum outside in the street. Not very convenient, right? And when the first portable electric vacuum was invented in 1905, it weighed 92 pounds...also not very convenient!

      Vacuums have undergone many modifications over the years, going from simple carpet sweepers to high-powered electric suction machines. The vacuum cleaner as we know it was invented by James Murray Spangler in 1907. He used an old fan motor to create suction and a pillowcase on a broom handle for the filter. He patented his 'suction sweeper,' but soon after that, William H. Hoover bought his patent and started the Hoover Company to manufacture the vacuum cleaners. Hoover's ten-day free trial and door-to-door sales soon placed vacuum cleaners in homes all over the country. Over the years Hoover added components (such as the 'beater bar') to dislodge dirt in the carpet so the vacuum could suck it up.

      Vacuum cleaners work because of Bernoulli's Principle, which states that as the speed of air increases, the pressure decreases. Air will always flow from a high-pressure area to a low-pressure area, to try to balance out the pressure. A vacuum cleaner has an intake port where air enters and an exhaust port where air exits. A fan inside the vacuum forces air toward the exhaust port at a high speed, which lowers the pressure of the air inside, according to Bernoulli's Principle. This creates suction - the higher pressure air from outside the vacuum rushes in through the intake port to replace the lower-pressure air. The incoming air carries with it dirt and dust from your carpet. This dirt is trapped in the filter bag, but the air passes right through the bag and out the exhaust. When the bag is full of dirt, the air slows down, increasing in pressure. This lowers the suction power of your vacuum, which is why it won't work as well when the bag is full.

      Click here to make your own simple vacuum cleaner!

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