Snell\'s Law Experimental Report PDF

Preview

Summary

An experimental report to prove Snell's Law by examining the refraction of light through a Perspex Block...

Description

Experimental Design: Snell’s Law Context: Snell's law is about the speed of light in different media. The law states that when light passes through different materials (for example from air to glass) the ratio of sines of the incidence (incoming) angle and the refraction (outgoing) angle does not change: sin 1 𝑣1 𝑛1 = = sin 2 𝑣2 𝑛2 where, sin 1 is the sine of the incidence ray, sin 2 is the sine of the refracted ray, 𝑣 is the velocity of the light in the medium, and 𝑛 is the refractive index of the medium

Aim: To prove Snell’s law by comparing the sine of the incidence ray and the sine of the refracted ray to find the refractive index of Perspex. Hypothesis: The sine of the incidence ray divided by the sine of the refracted ray will create a constant linear relationship which is known as the refractive index which will be 1.495. Equipment: • LED Light source • Perspex block • Protractor • Paper • Pencil • Blutack Variables: Independent Variable Dependent Variable Constant Variable

Angle of Incidence Angle of Refraction Type of paper, colour and type of light source, pencil used, person measuring angle, person drawing diagrams, size of Perspex

Risk Assessment: Hazard Nature of Hazard or Precautionary action associated risk of harm Perspex

Dropping it on your foot

Wear leather shoes

Light Source

Shining it into eyes and causing eye damage

Use a LED light source rather than a laser

Batteries

Misuse of batteries can cause overheating, rupture or leakage

Use new batteries and remove batteries when not in use

LED Light Source Lid

Young children chocking on it

Ensure the experiment is done in a safe, childfree environment

Emergency Procedure or remedial action in event of accident Make the afflicted person sit down and seek help Close the eyes of the afflicted person and seek help Clear the area around the leaked or ruptured battery, seek an adult, and clean surrounding area DRSABCD

Method: 1. All sources of light were removed 2. The paper was folded into fifths landscape 3. The piece of paper was blutacked onto the table 4. A line was drawn 2cm from the top landscape 5. The LED light source was placed down the middle of the page and the light beam was drawn lightly 6. The Perspex block was placed so the light refracted 7. The light’s new path was measured on the other side of the Perspex block 8. A line from the point the top side of the Perspex block was joined with the bottom line, as to show the light’s path through the Perspex 9. The normal was drawn on the top side of the Perspex glass 10. The incidence angle and refracted angle was measured using a protractor 11. The information was recorded in a table 12. Steps 3-9 was repeated but at different angles

Diagram:

Paper Perspex Block

LED Light Source

Results:

Results Analysis:

Sine of Incidence Angle vs. Sine of Refracted Angle 0.8

0.7 0.6

Sin r

0.5 0.4 0.3 0.2 0.1 0 0.00

0.10

0.31

0.33

0.45

0.62

0.64

0.80

0.82

0.92

0.92

0.97

0.98

Sin i

The sine of the incidence angle is directly proportional to the sine of the refracted angle and creates an increasing line when graphed.

Sine of Incidence Angle vs. Refractive Index 1.55

1.5

Refractive index

1.45 1.4

1.35 1.3 1.25

1.2 1.15 1.1 0.10

0.31

0.33

0.45

0.62

0.64

0.80

0.82

0.92

0.92

0.97

0.98

Sin i Refractive Index found

Refractive Index of Perspex

The sine of the incidence ray compared to the sine of the refractive index is a constant.

Discussion: The experiment had three areas that could have been improved. Firstly, the experiment was conducted over 2 days, meaning two different Perspex blocks were used. This could cause minute differences in data collected. To remedy this, it would be better to use the same Perspex block throughout the course of the experiment. Secondly, a protractor only to the nearest degree was used to measure the angles, meaning the angle could only measure to 0.5 accuracy. A protractor with measurements to minute of arc would be more accurate. However, the same protractor was also used throughout the whole experiment to ensure the measurements were more accurate. Another error was that the light source used produced a light that was wide and so it was difficult to consistently measure the middle of the light beam. A light source which did not do this would be better if this experiment is repeated. However, all data collected was quantitative rather that qualitative to improve accuracy. The experiment was repeated 12 times to improve reliability and different angles were used to ensure the relationship found was reliable. All lights were turned off and the room was kept as dark as possible to eliminate this variable. The same type of paper was used for each trial to keep this variable consistent and the same person measured all the angles to ensure it was measured consistently and the same person drew the path of the light beam to make sure there were no inconsistencies when drawing the light beam. All variables were kept consistent and the only variable being changed was the angle of incidence (independent variable) which caused the angle of reflection to change (dependent variable). Snell’s law of refraction was proved by this experiment as the sine of the incidence ray divided by the sine of the reflected ray created a straight increasing line when graphed. This is also supported when graphing the sine of the incidence ray against the refractive index of Perspex found as it produced a constant of 1.495. This is correct as a paper by the University of Adelaide showed “the actual value for the absolute refractive index of Perspex is 1.495.” In society, Snell’s law of refraction can prove useful in many products. Many do this my taking advantage of total internal reflection. Once the angle of incidence passes the critical angle, total internal reflection occurs. One example is optical fibres. Optical fibres are thin rods of high-quality glass that transmit information by total internal reflection by either visible light signals or infrared light signals. Optical fibres can carry more information and the signals do not weaken as much over long distances compared to an ordinary cable of the same thickness Conclusion: The refractive index of Perspex is 1.495, which was found by dividing the sine of an incidence ray by its refracted ray. The hypothesis, “The sine of the incidence ray divided by the sine of the refracted ray will create a constant linear relationship which is known as the refractive index which will be 1.495” is supported by the results collected. Bibliography: https://usc.adelaide.edu.au/asistm/optics/totalinternalreflection.doc http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/radiation/sendingrev1.shtm l https://columbusphysics.wikispaces.com/Snell%27s+Law+and+Index+of+Refraction...