Optics Devices: Overhead Projecter

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by saad123
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Optics Devices: Overhead Projecter

HOW IT WORKSThe main component of an overhead projector is the base. This base contains a clear glass top with an interior light. A small fan on the back of the unit removes heat that is produced by the light, preventing the overhead projector from overheating.When the light is turned on, the only portion of the base that lets light escape is the glass top; this causes a portion of the light to illuminate the glass as well as anything placed on top of it. Clear plastic projector sheets are placed on the glass with whatever image or text is to be displayed, letting the light shine through the sheet so that it can be projected

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HistoryThe first overhead projector was used for police identification work. It used a cellophane roll over a 9-inch stage allowing facial characteristics to be rolled across the stage. The U.S. Army in 1945 was the first to use it in quantity for training as World War II wound down. It began to be widely used in schools and businesses in the late 1950s and early 1960s.A major manufacturer of overhead projectors in this early period was the company 3M. As the demand for projectors grew, Buhl Industries was founded in 1953, and became the leading US contributor for several optical refinements for the overhead projector and its projection lens. In 1957, the United States' first Federal Aid to Education program stimulated overhead sales which remained high up to the late 1990s and into the 21st Century.

Advantages 1.Color can be used. 2. Transparencies may be written on and then the writing can be removed afterwards. 3. Transparencies are easy to prepare. 4. Overlays can be used for sequenced presentations. 5. Transparencies are reusable. 6. They can be used with both large and small groups. 7. Transparencies can be used with normal room lighting. 8. Overhead projectors are simple to operate. Disadvantages1.The overhead projector, while educationally a bargain, costs money, especially if each classroom is to have one. 2. As with any mechanical device, moving the projector around can result in damage.


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