![]() It follows that the wavelength of light is smaller in any medium than it is in vacuum. Where λ λ is the wavelength in vacuum and n is the medium’s index of refraction. As it is characteristic of wave behavior, interference is observed for water waves, sound waves, and light waves. Here we see the beam spreading out horizontally into a pattern of bright and dark regions that are caused by systematic constructive and destructive interference. Passing a pure, one-wavelength beam through vertical slits with a width close to the wavelength of the beam reveals the wave character of light. The laser beam emitted by the observatory represents ray behavior, as it travels in a straight line. In Figure 17.2, both the ray and wave characteristics of light can be seen. Interference is the identifying behavior of a wave. However, when it interacts with smaller objects, it displays its wave characteristics prominently. As is true for all waves, light travels in straight lines and acts like a ray when it interacts with objects several times as large as its wavelength. The range of visible wavelengths is approximately 380 to 750 nm. Since different colors diffract by different amounts, white light seen through a diffraction grating will spread out into its component colors as shown in this YouTube of incandescent and florescent diffraction.Where c = 3.00 × 10 8 c = 3.00 × 10 8 m/s is the speed of light in vacuum, f is the frequency of the electromagnetic wave in Hz (or s –1), and λ λ is its wavelength in m. A diffraction grating is a piece of glass or plastic with a series of very small grooves, each of which acts like a slit.Why is the light pattern complicated instead of a simple spot? What is the difference in the light pattern between the single slits and the double slits? Finally the laser is shone through a series of double slits. Then the laser is shone through single openings of different sizes. The first is a square opening, the second a hexagonal opening. A red laser beam is shone through several different small openings. Notice that the plane waves on the right spread out into a circle on the left after passing through the small opening. You are looking down onto the surface of a tray of water. Here water waves travel through an opening about the same size as the wavelength and change their direction. Likewise sunsets are orange because when the sun is on the horizon the path the light travels to reach us passes through more atmosphere and even more violet/blue is removed. The sun looks a little more yellow than it really is because the violet/blue part of the spectrum has been removed (scattered out in other directions). ![]() Violet and a little blue light is scattered but since our eyes are not as sensitive to violet we see the blue. The sky is blue because clusters of nitrogen and oxygen molecules (which make up most of the atmosphere) have resonances at the same frequency of violet light. The wave is first absorbed and then re-emitted in all directions (or sometimes perpendicular to the incident direction). Scatteringis a similar phenomenon that occurs when a wave interacts with an object that has a resonance frequency the same as the wave frequency. ![]() We only notice diffraction when the opening or object is close to the size of the wavelength, so to see diffraction of light it needs to pass through a much smaller opening than a doorway.
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