Experiment 5 - 1 Experiment 5. Atomic Spectra PHY 134...

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1 Experiment 5. Atomic Spectra PHY 134 (Section 11)
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2 Purpose The purpose of this experiment was to observe the spectra of lamps containing different elements using diffraction grating. The value of wavelength (λ) and energy level (n) of each color was calculated from the experiment and was compared with the chart on the wall. Apparatus Hydrogen lamp, Diffraction grating, rulers, aperture, household (regular) lamp, Sodium (Na) lamp, Mercury (Hg) lamp, and Neon (Ne) lamp Theory The diffraction grating provides the simplest and most accurate method for measuring wavelengths of light. It consists of a very large number of fine, equally spaced, parallel slits, usually thousands of lines (slits) per centimeter. Diffraction refers to the "bending" of waves around sharp edges or corners. The slits of a grating give rise to diffraction and the diffracted light interferes so as to set up interference patterns. Complete constructive interference occurs when the phase or path difference is equal to some whole number of the wavelength. In general the grating equation for constructive maxima is mλ = dsinθ. Here, m is the order of the spectrum, λ is the wavelength, d is the spacing between grating lines, and θ is the diffraction angle measured with respect to the direction of the light incident on the grating. Since the θ is very small, in this experiment, sinθ ≈ tanθ ≈ y/L. So, the equation can be rewritten as mλ =dy/L. The light appears as bright lines separated by dark regions: hence, the name line or discrete spectra. Each line has its own characteristic spectrum. The discrete lines of a given spectrum depend on the atomic structure of the atoms and are due to electron transitions. The
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3 line spectrum of hydrogen was shown to follow the description of Balmer's empirical formula: 1/ λ = 0.01097{(1/4)-(1/n 2 )}. Here, n refers to the energy level. Procedure First, the value of L and d were measured and recorded. Here, the value of d in centimeter was converted to nanometer. Then, the y value was measured for each bright color on both sides of the aperture. Using the data and the formula mλ =dy/L, wavelength was calculated for each color. Then, the results were compared with the chart on the wall. Using the formula 1/λ =
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Experiment 5 - 1 Experiment 5. Atomic Spectra PHY 134...

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