What are those two locations you can assume that the

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at two locations. What are those two locations? You can assume that the water surface is perpendicular to the side of the container. 4. Write down the expressions for Snell’s law at these two locations. Remember the one location is the critical situation where the beam ceases to leave the water. How is this critical situations expressed with Snell’s Law? Also write down a 31
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TOTAL INTERNAL REFLECTION – 1202Lab1Prob8 trigonometric relationship that relates angles at these two locations. You should have 3 relationships. 5. One relationship should be solvable for the critical angle of the first part of the prediction. The other two relationships can be manipulated to solve for the angle of the trajectory of the incident laser beam in terms of the critical angle. P REDICTION First, calculate the angle at which the beam ceases to exit the surface of the water. The angle is measured from the normal to the surface to the trajectory of the beam. E XPLORATION Warning: Laser beams may cause permanent vision impairment or blindness. Do NOT allow the laser beam (or its reflection) to point into anybody's eye. To avoid stray beams in the laboratory, make sure beams from your laser terminate on a screen at all times. Laser beams are extremely intense compared to light from any common light source (even compared to sunlight, as viewed from earth). Permanent blindness may result from prolonged exposure to any laser beam, even those from small laser pointers. Arrange the container and shine the laser through the container. Adjust the trajectory of the laser and observe where the beam ends up so that you can determine if it exits the water surface. As you adjust the laser trajectory, does the resultant beam move in a continuous or gradual manner or does it abruptly change? What would you expect? M EASUREMENT Once you have a solid understanding of the limitations of your measurements proceed to measure the angles. A NALYSIS Compare your angle measurements to your predicted values. Are they within your uncertainty? If not, reevaluate your uncertainty and/or take your measurements again. What is the minimum percent error you can attain? 32
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