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General Properties of Light

Since light acts like a wave, it has a wavelength. Light of different wavelengths goes by different names. (See Figure 13-1.)

Light waves of a very long wavelength (greater than one centimeter) are used for broadcast, so the information about television images is encoded on the light waves and broadcast to your television set, if you have one. These are called radio waves or microwaves.


Much of the heat from an electric heater is transported by infrared radiation, with wavelength on the order of 10–5 m to 10–4 m.
If light of a wavelength between 400 nm and 700 nm enters the pupil of your eye, it is likely to interact with the electrons of certain cells in the retina, producing a chemical change in the photoreceptor cells, leading to an action potential in one (or several) neurons. For this reason, light in this range is called visible light.
Light with shorter wavelength is ultraviolet light, responsible for sun tans and melanoma.


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Figure 13-1


X-rays have shorter wavelength still (less than 10–9 m) and can pass through much biological tissue, but not so easily the calcium in bones. They are used in imaging. Nuclear decay produces gamma rays (see Chapter 16), which have even shorter wavelengths, and this is the most penetrating electromagnetic radiation. Gamma rays are able to pass through the Earth like visible light passes through glass.
Light waves can be polarized. In fact, the light from the sky is polarized in most places, as well as light which is reflected from the hot layer of air on a desert road. You can detect the polarization using polaroid glasses. Look through the glasses at the shimmering surface of a hot road and rotate the glasses. You can see the light become dimmer and brighter.
To see what is happening, look at Figure 13-2. Beth is waving her hands up and down sending waves to Sam. The waves easily pass through the picket fence as it stands, but if the slats were horizontal, the waves would not be transmitted to Sam. Polaroid glasses allow the vertically polarized portion of light to go through but absorb the horizontally polarized portion.

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Figure 13-2

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