All about light

Here are the major things we have learned about light.

Light can carry both energy and information. It both is the way the sun delivers energy to the world, making life possible, and it is a very important way that we learn about the world, through our sense of sight.

Part of the information content of light is just the direction it is travelling -- light travels in straight lines, so that when we see a bird in a certain direction, we usually assume that there is a bird there. But lenses and mirrors are devices to change the direction light is travelling.

The brightness of a light is a measure of the rate of delivery of energy; if we saw the world only in black and white, vision would be hardly more than a determination of where the sources of energy seemed to be.

White light (both light from the sun and household lighting) is a mixture of lights of many different frequencies or wavelengths. The recipe that describes this combination is called the spectrum. A diffraction grating is a tool that lets us separate white light (which is a mixture of light of many wavelengths) into its components. It is a way to distinguish and identify light that comes from different sources.

The sense of sight is greatly enriched by the perception of color. Color is related to a physical property of light; however, light is even more complicated than our eyes reveal, because there are physically distinguishable kinds of light that are perceived as the same color.

There are many kinds of light that we cannot see, though they can be detected in other ways. Visible light is necessary in order for us to see. In the absence of visible light, we see nothing.

The branch of science and technology that studies light is called optics.  Optics investigations can reveal important properties of light.  A understanding of the properties of light and of materials can be applied to control light in many situations.  The most basic fact of optics is that light travels in a straight line in a uniform medium. This leads directly to the concepts of shadows and light beams. A light beam is light travelling in just one direction. It is the opposite of a shadow, and so you can't understand one without understanding the other.

We studied how light is affected by optical elements such as lenses and mirrors. When light is reflected by a mirror, the reflected beam is related to the incident beam by a geometrical relationship: the angles the two beams make with the mirror are the same. This is even true for curved mirrors.

Light also can change direction when it moves from one medium to another. This is the physical basis for lenses.

Lenses and curved mirrors can cause parallel light beams to become convergent (to a focal point, giving a real image) or divergent (giving a virtual image).

All light carries energy. A lens does not change the rate that energy is carried by the beam, but may concentrate it into a smaller area, or spread it out. The ability of light to cause chemical and physical reactions depends on its wavelength; light from the blue end of the spectrum (including ultraviolet light and Xrays) is generally more capable of having an effect than light from the red end.

This is the end of the Virtual Workshop on Light. Congratulations!

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