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October, 2006
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Confined Spaces: A space which has limited openings for entry and exit combined with unfavorable natural ventilation such as Caves, refrigerators, deep tunnels, pipelines, sewers, silos, tanks, vats, mines, deep trenches or pits, vaults, manholes, chimneys, etc.

Reflection and Refraction

JoVE 10409

Source: Derek Wilson, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

Light travels at different speeds depending on the material through which it is propagating. When light travels from one material to another, it will either slow down or speed up. In order to conserve energy and momentum, the light must change the direction in which it propagates. This bending of light is known as refraction. Some fraction of the light is also reflected at the interface between the two materials. In special cases, a light beam can be refracted so sharply at an interface that it is actually completely reflected back into the medium from which it was coming. Lenses make use of the principle of refraction. Lenses come in two varieties with different curvatures: convex lenses and concave lenses. Convex lenses are often used to focus light but can also be used to create magnified images of objects. When a convex lens causes the light rays coming from an object to diverge, the human eye judges the light to be coming from some point behind the actual object from which the light is originating. The image of the object will in this case be magnified. This type of image is called a virtual image. Concave

 Physics II

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