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Photoelectric_Sean_Tulin - Sean Michael Tulin...

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Sean Michael Tulin [email protected] 228 E. University Pkwy. Baltimore, MD 21218 410-662-9381 Intermediate Physics Lab The Photoelectric Effect Abstract: By exploiting the Photoelectric Effect, we demonstrate the corpuscular nature of light, and experimentally deduce Planck’s constant, the constant of proportionality between the energy and frequency of a single light quantum. Introduction: In the early 20 th century, Albert Einstein, excited with his recent work in Relativity and the Photoelectric Effect, wrote to a colleague to share his new ideas; the former contained interesting mechanics, he said, but the latter was truly revolutionary. Indeed, the Photoelectric Effect overthrew centuries-old classical theory which maintained that light was a wave, and helped cement the foundation of the Quantum Mechanical revolution. In this experiment, we examine the key features of the Photoelectric Effect; i.e., demonstrating contradictions to the classical theory of light waves and evidence for a theory of light quanta, measuring the proportionality between the energy and frequency of a light quantum, and measuring the work function, the energy needed to free an electron from the photoelectric plate.
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Procedure: The experimental apparatus was as follows: A white light beam was shined from a mercury vapor lamp and, passing through a lens/diffraction grating, spread into a fan of its individual component colors. The location of the lens/diffraction grating was adjusted (in the direction of light propagation) to sharpen the resolution of light on the detector. The detector could be rotated to intercept any single maxima of the rainbow diffraction pattern. In addition, the detector window could be masked with up to three different filters: a yellow filter (i.e., one which allows only yellow light to pass through), a green filter, and an intensity filter, to block a fraction of incoming light regardless of color, which itself was subdivided into five subsections: 20%, 40%, 60%, 80%, and 100% transmission. When measuring a green or yellow maximum, their respective filters were used to mask ambient room light and overlying higher-order maxima from higher frequencies from the light source. Inside the detector, light incident on the photoelectric plate, the anode, ejected electrons onto the cathode. Since the maximum kinetic energy of an ejected electron was limited by the energy, and thus the frequency, of the light quantum which dislodged it, once sufficient charge had accumulated on the cathode, the potential difference between anode and cathode would be too great for a single electron to surpass. The relationship between this potential difference (hereafter, termed ‘stopping potential’), the electron kinetic energy, and the photon energy and frequency will be examined in more detail later. The experiment itself consisted of the following measurements: the
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Photoelectric_Sean_Tulin - Sean Michael Tulin...

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