Diffraction of light

What causes the light and dark rings surrounding the shadow of this object?If you shine light at a small object, such as the paper clip in the figure at right, you’ll see something peculiar: a series of bright and dark rings (or bands) surrounding the shadow of the object! This diffraction pattern of bright and dark bands is caused by constructive and destructive interference when light passes around a barrier or through an opening. Read the text aloud
How do diffraction and interference create this pattern? On page 833, you learned how waves diffract around the edge of an obstacle. Sound waves can diffract around the wall of a room, but light waves cannot, because the wavelength of light is much smaller than the size of the barrier. What happens if you use a smaller barrier, such as a paper clip? Does light diffract around it? Read the text aloud
Diffraction pattern due to wave interference around a barrierWhen light waves pass a barrier, a little bit of the light’s intensity diffracts around the barrier’s corner. These waves can interfere with light waves diffracting around the other side of the barrier, which creates a pattern of interference. If the diffracted light is projected onto a screen, such as in the illustration at the top of this page, you will see a pattern of bright and dark bands around the edge of the barrier. The bright bands are constructive interference, whereas the dark bands are destructive interference. The brightness of the interference bands falls off away from the edge of the barrier. Read the text aloud Show Resolution of telescopes
The illustration at the top of this page shows this diffraction pattern for light passing around a paper clip. The diffraction pattern of light is an example of how light can behave like a wave. Read the text aloud
Monochromatic light has the same wavelengthThe diffraction pattern is difficult to see when you use ordinary, white light. Diffraction is a wave phenomenon, so it is best demonstrated when all the light has the same wavelength. Light waves are called monochromatic if they have the same wavelength, although they may differ in amplitude or phase. Consider the green light color of the illustration at the top of the page. A monochromatic, green light source was used to create it. Furthermore, the light must be coherent or in phase to see the interference pattern from diffraction around a barrier. Lasers are often used as sources of coherent light. Read the text aloud

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