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# To determine the refractive index of glass

Extracts from this document...

Introduction

PHYSICS COURSEWORK LAB REPORT

Aim: To determine the refractive index of glass.

Hypothesis: The incident ray, the normal and the refracted ray all lie in the same plane. Also, according to Snell’s law, for 2 particular media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction should be a constant:

Sin i

Sin r

Apparatus:

1. A rectangular prism
2. Four 1 inch pins

Middle

The rectangular prism is placed at the middle of the top of the page and its perimeter is traced with the help of the ruler and pencil. The normal is soon after marked out in the approximate centre of the perimeter using the protractor at the 90 degrees point.  The operation is then repeated at the middle of the bottom of the page and finally to the back of the page.4 perimeters with a normal on each should already be drawn at that stage. Next, an angle should be measured and traced from the point where the normal touches the perimeter line from any of the 4 sketch. The angle is noted at the table as an angle of incidence.

Conclusion

Results

Conclusion

The results seem satisfying enough to support the hypothesis, hence supporting the idea of the law of refraction.

Evaluation and precautions

• Blue tack was used so as to keep the paper stable while working to prevent errors.
• A double check with another protractor was performed to ensure its accuracy.
• Mistakes such as not perfectly vertical pins stuck or not exactly parallel positioning of the eye could have been performed relying on the results.
• Parallax errors or other mistakes such as too bumpy cardboard may have lead to not accurate enough results.
• Another method of performing the experiment yet roughly the same precision would be to use light beams which would be more accurate than our eyes’ positioning therefore reducing parallax error.

This student written piece of work is one of many that can be found in our GCSE The Earth and Beyond section.

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## Here's what a star student thought of this essay

4 star(s)

### Response to the question

The candidate has planned and carried out an investigation into Snell's Law. They have measured the angles or incidence and refraction of beams of light through a glass block, and used their data to support their conclusion that Snell's Law ...

### Response to the question

The candidate has planned and carried out an investigation into Snell's Law. They have measured the angles or incidence and refraction of beams of light through a glass block, and used their data to support their conclusion that Snell's Law is true. They have included hypothesis, method, results, conclusion, and evaluation sections. However, they could have gone into more detail in some areas, such as the suggestions for improvement in the evaluation section. However, they have still managed to carry out the experiment well and therefore come to a well supported conclusion.

### Level of analysis

The candidate has manipulated their results well by using mathematical functions, including the sine function. However, they have made the common error of giving their results of their calculations to a higher degree of accuracy than their original data - it would have been better to record the angles to two significant figures (not just in increments of 5 degrees) in order to improve the accuracy of their results. They could also have improved their analysis by including a graph - for example a graph of the sine of the angle of incidence to the sine of the angle of refraction.
They have considered the possible causes of error in their data in their evaluation section, along with suggestions for improvement, although they could have described these a bit more clearly.
Overall, their excellent mathematical manipulation of the original data should have gained them good marks, and they should only have been slightly held back by these small issues.

### Quality of writing

Their spelling, grammar, and punctuation is excellent throughout. They have generally explained and described things clearly, but their method section in particular could have been improved by a labelled diagram. The report is organised well into well-titled sections, the only noticeable issue here is the lack of a 'reducing uncertainties/ errors' section, which is an essential part of the method. However, much of the information which should have been here has been included in the evaluation.

Reviewed by dragonkeeper13 18/07/2012

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