![]() Light waves may change direction at the boundary between two transparent materials. ![]() This, too, is the same change in direction as for light going from slow to fast.Different materials have different densities. When going from the grass to the footpath, the front wheels can move faster and the mower changes direction as shown. This is the same change in direction as for light when it goes from a fast medium to a slow one. Going from the footpath to grass, the front wheels are slowed and pulled to the side as shown. In both cases, you can imagine what happens by thinking about pushing a lawn mower from a footpath onto grass, and vice versa. Conversely, as shown in Figure 2.3.9(b), the direction of the ray moves away from the perpendicular when it speeds up. Note that as shown in Figure 2.3.9(a), the direction of the ray moves closer to the perpendicular when it slows down. This means that the speed of light is less in medium 2 than in medium 1. In the situations shown in Figure 2.3.9 medium 2 has a greater index of refraction than medium 1. ![]() The change in the speed of light is related to the indices of refraction of the media involved. (Some of the incident light will be reflected from the surface, but for now we will concentrate on the light that is transmitted.) The change in direction of the light ray depends on how the speed of light changes. The angles are measured relative to a perpendicular to the surface at the point where the light ray crosses it. These concepts are especially important for understanding techniques in optical mineralogy and petrology.įigure 2.3.9 shows how a ray of light changes direction when it passes from one medium to another. We will discuss refraction in more detail and introduce polarization of light in the sections below. On leaving the raindrop, the red rays have turned through a smaller angle than the blue rays, producing a rainbow. White light separates into different colors (wavelengths) on entering the raindrop, as red light is refracted by a lesser angle than blue light. Scattering and refraction in a raindrop to produce a rainbow. For example, when the full spectrum of visible light travels through the glass of a prism, or through a raindrop, the wavelengths are separated into the colors of the rainbow. ![]() Different wavelengths of light are slowed at different rates, which causes them to bend at different angles. As light travels into a different medium, the change in speed bends the light. Light travels slower in air than in a vacuum, and even slower in water. Refraction is when light waves change direction as they pass from one medium to another. Even though violet is scattered more than blue, the sky looks blue to us because our eyes are more sensitive to blue light. This scattering of light at shorter wavelengths illuminates the skies with light from the blue and violet end of the visible spectrum. Longer wavelengths of light-red and yellow-transmit through the atmosphere. Light at shorter wavelengths-blue and violet-is scattered by nitrogen and oxygen as it passes through the atmosphere. The sky appears blue because of this scattering behavior. The amount of scattering that takes place depends on the wavelength of the light and the size and structure of the object. Scattering occurs when light bounces off an object in a variety of directions. A CD demonstrating diffraction from grooves in the surface, producing iridescent colors. The figure below shows the grooves on a CD diffracting visible light and producing iridescent colors. In the case of visible light, the separation of wavelengths through diffraction results in a rainbow. It is most pronounced when a light wave strikes an object with a size comparable to its own wavelength. This video reviews the concepts of absorption, transmission, and reflection of light:ĭiffraction is the bending and spreading of waves around an obstacle. When a light wave encounters an object, it is either transmitted, reflected, absorbed, refracted, polarized, diffracted, or scattered depending on the composition of the object and the wavelength of the light. Light waves across the electromagnetic spectrum behave in similar ways. Elizabeth Johnson and Juhong Christie Liu Behavior of Light
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