# Find a relationship between the angles of incidence and the angles of refraction by obtaining a set of readings for the angles of incidence and refraction as a light ray passes from air into perspex.

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Introduction

Refraction of Light Aim: To find a relationship between the angles of incidence and the angles of refraction by obtaining a set of readings for the angles of incidence and refraction as a light ray passes from air into perspex. Introduction: Refraction is the bending of a wave when it enters a medium where it's speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law. (Refer to diagram below) The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium. In this experiment, the index of refraction for the perspex is 1.50. Snell's Law relates the indices of refraction of the two media to the directions of propagation in terms of the angles to the normal. It refers to the relationship between the different angles of light as it passes from one transparent medium to another. When light passes from one transparent medium to another, it bends according to Snell's law which states: where: n1 is the refractive index of the medium the light is leaving, n2 is the refractive index of the medium the ...read more.

Middle

Difficulties encountered and how they were overcome: * Accuracy of angles: used a protractor to measure * Accuracy of refractive angles as the beam thickened as it passed through the perspex: measured and marked a point on the grid as closely as possible to the narrowest part of the light ray. * Ensuring that the light went through the centre of the perspex: repeated each angle 2-3 times to be sure of the results acquired * Keeping the perspex stable: one person held the perspex while another marked the points. Results: The results obtained were as accurate as possible, and covered a range of angles, from 0 degrees to 80 degrees and not above that, as the light ray would have been reflected. Also, the results obtained were narrowed to + or - each side of the result. Lastly, the results from three other students in the class were compared and then averaged to ensure accuracy. Angle of Incidence Angle of Refraction Average Sin Incidence Sin Refraction sin i/sin r 0 0 0 0 0 0 0 0 0 10 7 7 6 7 7 0.174 0.116 1.503 20 13 12 13 14 13 0.342 0.226 1.513 30 19 22 20 20.5 19 0.5 0.327 1.528 40 25 25 24 24.5 25 0.643 0.416 1.547 50 31 31 31 32 31 0.766 0.515 1.487 55 33 31.5 32 32.5 33 ...read more.

Conclusion

* The protractor, only measuring to an accuracy of 1 degree, which may cause the results to be slightly inaccurate. * Thick refractive light ray which may have cause a difference of almost 3 degrees. * The ray of light passing right through the middle of the perspex. Uncertainty of data and calculations: * Making precise, exact line of the light rays * Parallax error * Estimation of where to draw point Expected and derived relationships or physical values: * The expected result for the relationship between the incident angle and the refracted angle is a constant, 1.50 which is the relative index for the perspex. The derived results are quite accurate, due to the result being obtained and averaged out by comparing the results of three other people. However, the result can be further improved by using a grid that has the protractor printed on it. This would make it easier, to read the angle of both the incident and refracted rays. Conclusion: The investigation of the relationship between the incident angle and the refracted angle was a success. The absolute refractive index of perspex was proven to be 1.50, although there were slight differences in the results. Also, the investigation proved that Snell's law is correct and that when light passes through a medium that is denser, it bends (refraction). Also, the gradient, of any graph plotted for sin i over sin r for particular material, results in a constant, which is its relative index. ...read more.

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