Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1665. As physical objects have wave-like properties (at the atomic level), diffraction also occurs with matter and can be studied according to the principles of quantum mechanics. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays, and radio waves. Similar effects occur when light waves travel through a medium with a varying refractive index or a sound wave through one with varying acoustic impedance. In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. If there is destructive interference, (the trough of one light wave meeting the crest of another), the light will either appear darker or disappear entirely.ĭiffraction can also be referred to a phenomena that occurs when a wave encounters an obstacle. If there is constructive interference, (the crests of two light waves combining), the light will appear brighter. When sunlight (or moonlight) encounters a cloud droplet, light waves are altered and interact with one another in a similar manner as the water waves described above. This concept also applies to light waves. However, if a crest of one wave and a trough of another wave combine, they cancel each other out to produce no vertical displacement (destructive interference). If the crests of two waves combine, an amplified wave is produced (constructive interference). As these waves spread outward in all directions from the float, they interact with other water waves. If water waves were incident upon a float residing on the water surface, the float would bounce up and down in response to the incident waves, producing waves of its own. To visualize this, imagine light waves as water waves. Optical effects resulting from diffraction are produced through the interference of light waves. The illustration below shows how light (from either the sun or the moon) is bent around small droplets in the cloud. An optical effect that results from the diffraction of light is the silver lining sometimes found around the edges of clouds or coronas surrounding the sun or moon. Diffracted light can produce fringes of light, dark or colored bands. In the atmosphere, diffracted light is actually bent around atmospheric particles - most commonly, the atmospheric particles are tiny water droplets found in clouds. For large apertures the wave passes by or through the obstacle without any significant diffraction. For very small aperture sizes, the vast majority of the wave is blocked. It occurs when the size of the aperture or obstacle is of the same order of magnitude as the wavelength of the incident wave. However, if the two are closer in size or equal, the amount of bending is considerable, and easily seen with the naked eye.ĭiffraction is also the spreading out of waves as they pass through an aperture or around objects. If the opening is much larger than the light’s wavelength, the bending will be almost unnoticeable. The amount of bending depends on the relative size of the wavelength of light to the size of the opening. Diffraction is the slight bending of light as it passes around the edge of an object.
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