A projector is a device that integrates a light source, an optics system, electronics and displays for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. These devices attach to a computer or video device as we can connect a monitor or television. An overhead projector is a variant of slide projector that is used to display images to an audience. An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it on top of which is a large fresnel lens that collimates the light.
The mirror allows both the presenter and the audience to see the image at the same time, the presenter looking down at the transparency as if writing, the audience looking forward at the screen. The height of the mirror can be adjusted, to both focus the image and to make the image larger or smaller depending on how close the projector is to the screen. The overhead projector facilitates an easy low-cost interactive environment for educators.
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