Diffraction – light as a wave. Examples of wave diffraction: . Water waves diffract through a small opening in the dam. Sound waves diffract through a crack on the wall. Light diffracts. Huygens’ principle of diffraction:
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Examples of wave diffraction:
Water waves diffract through a small opening in the dam.
Sound waves diffract through a crack on the wall.
Huygens’ principle of diffraction:
Wave front made of spherical wavelets travel to the small opening, those wavelets passing through this opening result in a spherical wave front with coherent wavelets.
Constructive interference, bright fringe
Destructive interference, dark fringe
So light diffracts because the wavelets interfere!
Coherent monochromatic light is incident on a slit whose width is 0.0211 mm. The diffraction pattern is viewed on a screen that is placed 3.12 m from the slit. The distance along the screen from the middle of the central maximum to the first dark fringe is 10.1 cm. What is the wavelength of the light?
m = 1, a = 0.0211 mm.
Solve for , = 683 nm.
When light passes through a circular aperture with a diameter comparable to the light wavelength, one sees diffraction patterns shown on the right photograph. The angle θ to the first minimum is:
2d sinθ = m
d = distance between planes of atoms
θ = angle between ray, plane of atoms
m = order of maximum
= wavelength.Another example of diffraction -- grating
X-rays reflected from a regular structure of a crystal creates diffraction pattern that can be used to measure the crystal structure. Like this diffraction pattern of a DNA molecule.