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Unformatted text preview: Chapter 10: Modern Physics Abstract: The purpose of this experiment was to explore several phenomena that are relevant to the field of modern physics. First, the speed of light was calculated by measuring the time it took for light to travel through a fiber optic cable of known length and index of refraction. The charge-to-mass ratio was supposed to be calculated using an electron tube with Helmholtz coils, but the apparatus was not working on the day of the experiment. Finally, an experiment was performed to calculate Plancks constant by measuring the knee voltage through LEDs of known frequency. 10.1 The Speed of Light 1. Time required to move through cable is 104 ns. 2. ( d/ t)= (20m/104e-9 sec) = 1.923e8 m/s 3. V = c/n Vn = c = [(1.923e8)(1.5)] = 2.8845e8 m/s 4. [abs(2.8845e8 3 e8)/3 e8] x 100 = 3.85% 5. Some possible sources of error for this experiment are with the oscilloscope itself as it has built in limits to its accuracy, and limits to the precision because we measure the change in time by placing the cursors with our eyes inexact. 6. Fizeau used a toothed wheel to help him measure the time taken for light to travel 12 miles. A converging lens gathered up the light rays from a powerful light source. A plate of glass was placed at an angle to these rays just before they would have been brought to a focus. Instead, the light rays were reflected and brought to a focus on one side of the glass plate. These rays were made parallel by a collimating lens placed so that the actual light focus coincided with the principal focus of the lens. The rays traveled in this parallel condition over a distance of about 6...
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