![]() Now let’s talk about diffraction gratings. However, we can get better resolution if we increase the number of openings to two or more. In a single slit experiment, the light pattern is not resolved very well, meaning that it gets brighter and darker gradually. The minima are created by destructive interference, where the light waves meet up out of phase, or crest to trough, and cancel each other out. The bright spots in the pattern, which we call “maxima”, are created through constructive interference, where the light waves meet up crest to crest or trough to trough and are combined, increasing the amplitude. From this equation, we can see that as we decrease the size of the aperture d, the angle at which the light diverges increases, meaning that it will be bent more with smaller aperture openings. Θ is the angle from the center of the screen to the minima being measured, λ is the wavelength of the light, d is the size of the aperture, and n is the number of minima you are away from the center (1,2,3…). The equation used to describe this pattern based on each individual dark spot is, sine of theta equals n times lambda over d. It creates a pattern with the brightest spot in the middle, which fades to a dark spot, then a light spot again that is slightly less bright on either side until the bright spot fades completely. This experiment is referred to as the single slit experiment. This pattern appears as a series of bright spots. When we shine a beam of light through a tiny aperture onto a wall or screen, we see a diffraction pattern. Since the water waves are similar in size to the opening in the wall, the bending of the waves is visible here. But, what happens when there’s a wall placed in the water with a small opening? Let’s take a look. If you’ve ever been to the ocean, you can imagine the waves of water rolling in. Since the wavelengths of visible light are very, very small, this phenomenon may not be very intuitive. If these two things are similar in size, then the light can be bent more. The amount that the wave bends depends on the size of the wavelength and the size of the opening, or aperture. So, the whole picture of dispersion is that the different wavelengths of light are absorbed differently by the atoms in the refractive medium, which results in slightly different indices of refraction and slightly different angles of refraction for each wavelength of light, thereby dispersing the light.ĭiffraction, on the other hand, refers to the phenomenon of waves bending as they pass through an opening or around the edge of an object. In other words, materials have a range of optical densities corresponding to different wavelengths. ![]() The amount of light absorbed by the refractive material depends on the wavelength of the light. The more optically dense a material is, the higher the index of refraction. The term used to measure the ratio of the speed of light in a vacuum, c, to the speed of light in a medium, v, is called the index of refraction: n=c/v, and it is also an indication of the optical density of a material. While light travels at about \(3 x 10^ m/s\) in a vacuum, it travels slower through any medium, depending on the optical density. The higher the optical density of a material, the slower light is able to pass through it. Refractive materials are described by their optical density, which is a measure of how much of the light gets absorbed by atoms in the material. They refract again once they leave the prism due to the differences in refractive properties between air and the prism. Shorter wavelengths (violet) get refracted more than the longer wavelengths (red). When white light hits the refracting surface, the different colors of light separate because of their differing wavelengths. Let’s take a look at each of them separately.ĭispersion occurs when light of different wavelengths, such as white light, hits a refracting surface, like a prism. Let’s get started!ĭispersion and diffraction are each descriptions of light interacting with matter in different ways, and both can be used to separate light of multiple wavelengths. ![]() Hi, and welcome to this video on the diffraction of light waves! In this video, we will compare and contrast diffraction and dispersion and take a look at how diffraction gratings work.
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