![]() ![]() However, since each color has a specific wavelength, the locations of the other interference maxima depend on the wavelength. All of the different wavelengths will constructively interfere in the center of the detector. If the concepts in Figure 1-8 are extended one step further and polychromatic light is used, the different colors of radiation are separated. The above discussion was for monochromatic radiation. The blue lines above correspond to the alignment of maximum constructive interference. Distinct bands are show here for illustrative purposes only the bands are actually broader areas of light (constructive interference) that gray to areas with no light (deconstructive interference). An Idealized Illustration of the Two-Slit Experiment Illustrating the Constructive and Deconstructive Nature of Electromagnetic Radiation. Instead of a sinusoidal variation in intensity, a series of narrow bright bands appears on the detector.įigure 1-8. a diffraction grating) the regions of constructive interference become very narrow. If the two slits are replaced by many narrow, equally spaced slits (i.e. Each of these situations is illustrated in Figure 1-8. Overall the intensity distribution on the detector varies sinusoidally, with high intensity corresponding to constructive interference, and zero intensity corresponding to destructive interference. Positions on the detection plate that correspond to odd integer multiples of half a wavelength create deconstructive interference, with no resulting intensity. Regions on the detector in which the path length difference between these two waves is an integer multiple of the wavelengths constructively interfere and produce a large intensity. Constructive and deconstructive interference between these beams can be observed on a flat plate (a detector in this case). As radiation is passes through the second slits, diffraction occurs at both slits creating two beams that spread out and overlap. The monochromatic light is passing through one narrow slit before being passed through two more slits. Start by considering monochromatic electromagnetic radiation passing through two slits (Figure 1-8). Variation in Slit Width Openings.ĭiffraction is intimately related to the constructive and destructive interference of waves. ![]() As the slit becomes more narrow (Figure 1-7b), the uncertainty in position becomes smaller which results in greater diffraction.įigure 1-7. When the slit is sufficiently wide, the diffraction is small because there is still great uncertainty in position (Figure 1-7a). The Heisenberg Uncertainty Principle indicates that as the uncertainty in the position of a photon decreases (in a direction transverse to its propagation direction), the uncertainty in its transverse momentum must increase this uncertainty in transverse momentum is what causes the light to spread out. As the slit width narrows waves of radiation spread out more strongly. In order to more easily understand how diffraction can be used to disperse wavelengths, picture the passage of radiation through a narrow barrier. ![]() The manipulation of diffraction forms the basis of selecting a narrow range of wavelengths of light in a monochromator. Because diffraction depends on the wavelength of light, it can be used to separate polychromatic light (white light) into its constituent optical frequencies in the case of white light, this would result in a rainbow of colors. An interesting distraction effect was observed in a laboratory setting by Thomas Young in 1801 when he performed the two-slit experiment (discussed below). Diffraction is a process in which a collimated beam of radiation spreads out as it passes (1) though a narrow opening or (2) by a sharp barrier. ![]()
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