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DATA In the crystallography lab where you work, you are given a single crystal of an unknown substance to identify. To obtain one piece of information about the substance, you repeat the Davisson–Germer experiment to determine the spacing of the atoms in the surface planes of the crystal. You start with electrons that are essentially stationary and accelerate them through a potential difference of magnitude Vac. The electrons then scatter off the atoms on the surface of the crystal (as in Fig. 39.3b). Next you measure the angle θ that locates the first-order diffraction peak. Finally, you repeat the measurement for different values of Vac. Your results are given in the table.
Vac (V) | 106.3 | 69.1 | 49.9 | 25.2 | 16.9 | 13.6 |
θ (°) | 20.4 | 24.8 | 30.2 | 45.5 | 59.1 | 73.1 |
(a) Graph your data in the form sin θ versus
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