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# Find the critical angle and refractive index for plastic using a graphical treatment for my results.

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Introduction

Gurveer Saggu

Investigating Refraction

Aim: Find the critical angle and refractive index for plastic using a graphical treatment for my results.

Introduction: The Refractive Index is how the much a material bends the light. In this experiment I will be looking at the how much the angle of incidence gets refracted and I will multiply my results by sine. I will plot a graph from my results and, using a line of best fit, I will calculate the size of the angle of incidence in order for the refracted angle to be equal to 900 (critical angle). I will then calculate the refractive index by using Sine I and Sine R. I will be looking at light going from glass to air (from a dense medium to a lighter one).

Theory: Incident ray: Ray of light before refraction. Angle of refraction (R): Angle between refracted ray and normal at point of incidence. Angle of incidence (I): Angle between incidence ray and normal at point of incidence. Point of incidence: Point at which incident ray meets boundary and becomes refracted ray. Critical angle

Middle

Diagram:

Method:

1. Arrange the equipment as shown.
2. Then in the middle of the paper, draw around the block of plastic and keep it placed there.
3. Then around the curved part of the diagram mark out the normal line, then mark out the angles in 50 intervals.
4. Connect the PSU to the mains socket and then the ray box to the PSU.
5. Fit the slit on the ray box allowing only a small ray of light through.
6. Then turn on the PSU.
7. Then shine the light on the interval and make sure it comes out of the centre of the straight side.

Conclusion

0, then the answer would be 20% incorrect. By showing that the critical angle is slightly out by a degree either side shows that these marginal errors have been taken into account.

Evaluation: My method of carrying out the experiment was good and very simple to follow. Before this version of the experiment, I performed a trial and error attempt of the experiment to get an approximate idea of what the angle would be. Some errors were caused by simple things like rounding an angle to certain decimal places and misjudging an angle. If I were to redo the experiment again then I would take these factors into account and make sure that they would not have a significant effect on the final results. These improvements would make my results more accurate.

My results were valid as they allowed me to get an accurate line of best fit which was important in calculating the critical angle. The results were all along the line of best fit, which was as I had predicted. My results did not have any anomalies which did not affect my results. This conclusion led me to a final conclusion of the critical angle was 430 and the refractive index of the critical angle was approximately 1.28.

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4 star(s)

This is a well structured and well written report.
1. The sources of information need to be referenced.
2. The conclusion needs to quote data from the investigation to back up the patterns.
3. The evaluation should suggest further research opportunities.
****

Marked by teacher Luke Smithen 13/08/2013

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