Missing Figures
SINGLE SLIT DIFFRACTION PATTERN OF LIGHT
The diffraction pattern observed with light and a small slit comes up in about every high school and first year university general physics class. The intention of this paper is to explain this pattern at the academic level mentioned above. Light is interesting and mysterious because it consists of both a beam of particles, and of waves in motion.
WAVE PARTICLE DUALITY:
All carriers of energy and momentum, such as light and electrons, propagate like a wave and exchange energy like a particle.
It wasn't until the 19th century that convincing evidence was found showing that light behaves like waves. Before reading on, you may wish to review some wave terminology.
The key to understanding why light behaves like waves is in INTERFERENCE and DIFFRACTION.
Interference and Diffraction are the phenomena that distinguish waves from particles: waves interfere and diffract, particles do not.
Light bends around obstacles like waves do, and it is this bending which causes the single slit diffraction pattern.
Some assumptions must be made for this description of the single slit diffraction pattern:
* The slit size is small, relative to the wavelength of light.
* The screen is far away.
* Cylindrical waves can be represented in 2D diagrams as cicular waves.
* The intensity at any point on the screen is independent of the angle made between the ray to the screen and the normal line between the slit and the screen (this angle is called T below). This is possible because the slit is narrow.
point1
Consider a slit of width a, light of wavelength l, and a smaller than l.
When the light encounters the slit, the pattern of the resulting wave can be calculated by treating each point in the aperature as a point source from which new waves spread out.
pointb
Let L represent the distance between the slit and the screen.
Let T represent the angle between the wave ray to a point on the screen
and the normal line between the slit and the screen.
point2
The top part of the figure to the left is an imitation of a single slit diffraction pattern which may be observed on the screen (there would really be more blending between the bright and dark bands, see a real diffraction pattern at the top of this page).
Below the pattern is an intensity bar graph showing the intensity of the light in the diffraction pattern as a function of sin T.
through space. This theory came to life when Heinrich Hertz created those waves and seven
A typical X-ray diffraction pattern is in the form of a graph, with a series of peaks (the actual diffraction pattern), with the horizontal axis being 2θ, or twice the Bragg angle; and the vertical axis is the intensity, or the X-ray count measured by the detector, which is a function of the crystal structure and the orientation of the crystallites.
During the crisis of modern science in the late nineteenth and early twentieth centuries, the postulates of early scientific discoveries had been refuted. In one of science’s most defining moments, an undisturbed photon of light was found to exhibit both wave-like and particulate qualities. The relationship between these two qualities would later be termed complementarity by Niels Bohr, one of the scientists at the forefront of this discovery. As Thomas S. Kuhn notes in The Structure of Scientific Revolutions, “Before [the theory of quantum mechanics] was developed by Plank, Einstein, and others early in [the twentieth] century, physics texts taught that light was transverse wave motion” (12). So staggering was this discovery that in his autobiography, Albert Einstein recounts, “All my attempts to adapt the theoretical foundations of physics [to the new quantum knowns] failed completely. It was as if the ground had been pulled out from under one, with no firm foundation to be seen anywhere upon which one could have been built.” Not surprisingly, this arrest of the fundamental postulates of classical physics sparked a reevaluation of the “world view” by the ...
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Light and sound are similar in some ways too, though. They both have frequencies that humans cannot detect (ultraviolet, infrasonic, etc.). Since both of them are also waves, they can be made to interfere. They can also be made to reflect and refract.
Quantum mechanics was pioneered by Max Planck, who developed the formula E = hv—which is the base for much of the quantum mechanical field. Quantum theory (the origin of quantum mechanics), as described in Talking Tech, was, at its early core, a handful of theories and hypotheses regarding energy quantization and wave-particle duality (Rheingold and Levine). The book goes on to explain how this realm of science is basically an extension of physics attempting to derive a mathematical specification of how the entirety of the universe operates and behaves at the subatomic level. Conversely, it also describes how quantum theory also diverges from classical physics in that it stipulates that the only...
Some physical entities such as light can display some characteristics of both particles and waves. Before the early 20th century, scientists believed that light was in the form of an electromagnetic wave. It wasn’t until the 20th century onwards that scientists found that light has properties of waves and particles. Scientists discovered different properties of light through experimentation and allowed them to determine that light actually has a wave-particle duality.
Sir Isaac Newton held the theory that light was made up of tiny particles. Before, most theories of light had an unexplainable phenomenon. Einstein had suggested that tiny particles which have energy, called protons, formes into light. This suggestion was made when he proposed a solution to the problems of observations discovered on the actions of light having the characteristics of both wave and particle theory.
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waves are further divided into two groups or bands such as very low frequency (
Spectroscopy is measured using a spectrophotometer. A beam of light is first pointed towards the spectrophotometer. The beam of light then strikes a part of the spectrophotometer called the diffraction grating. The diffraction grating works similar to the prism shown above. It separates the light into its component wavelengths by rotating so that only a specific wavelength will reach a part of the spectrophotometer called the exit slit. On the other end of the exit slit there is a sample located in a test tube as well as a detector. After the wavelength passes through the sample, the detector measures the transmittance and absorption of the sample. The transmittance is the amount of light that was able to pass through the sample and reach the detector, and the absorption is the amount of light that was absorbed by the sample. The detector converts the measure of transmittance into s digital display, such as a graph.
Light is a series of self-propagating transverse waves composed of electric and magnetic fields in a fixed ratio. The distance between the crests of successive waves is known as the wavelength, denoted by the symbol λ (lambda), as shown in Figure 2. The frequency of a wave is defined as the number of waves passing through a given point per second.