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Compare the measured refractive index of three liquids against the unknown values and to then use the technique to measure the refractive of an unknown liquid.

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Introduction

Charlie Hyde 11C

Compare the measured refractive index of three liquids against the unknown values and to then use the technique to measure the refractive of an unknown liquid.

Diagram

Pilot

A pilot experiment was carried out, using a Perspex block.  The block was placed onto a piece of paper and drawn around to ensure that the block remained in the same place throughout the entire duration of the experiment. The normal was also drawn and from this, five different angles of incidence were drawn. These were placed at 10,20,30,40 and 50.  At each angle of incidence a ray of light was shone and the light that entered and exited the Perspex block was noted and the angle of refraction measured.

Method

Refraction is caused by the change in speed of light when it passes into a medium that has a different optical density to air or the medium through which it is passing.

A Perspex tank will be placed on a piece of paper and drawn around. Then the shape will be cut out. The tank will then stay in this position. The tank will be filled around 2/3 full of liquid.

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Middle

30°

21°

0.50

0.36

1.3

40°

29°

0.64

0.48

1.3

50°

40°

0.77

0.64

1.2

60°

41°

0.87

0.66

1.3

Oil

Angle of incidence (I)

Angle of refraction (R)

Sin I

Sin R

Refractive index (R.I)

Sin I

Sin R

10°

0.17°

0.10°

1.70

20°

12.5°

0.34°

0.22°

1.55

30°

20°

0.50°

0.34°

1.47

40°

27°

0.64°

0.45°

1.42

50°

32°

0.77°

0.53°

1.45

60°

36°

0.87°

0.59°

1.47

Ethanol

Angle of incidence

(I)

Angle of refraction

(R)

Sin I

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Conclusion

When testing ethanol, two beams of light could be seen on the paper because some light went over the shutter in the ray box.  So it was not necessarily clear as to which one was the correct angle of refraction.  Despite this, accurate results seem to have been obtained.

The experiment was reliable enough to complete the investigation safely, fairly and accurately.  It was an easy way of succeeding in finding out what was needed to be investigated.

However, although in the plan it said that each experiment was going to be repeated to check for errors and therefore make the results more accurate, there was not enough time to do so. So if there was an opportunity to do this investigation again, each experiment for each of the three liquids would be repeated. This would mean that an average could be taken and so the results would be even more accurate. 

To take the investigation even further, it could be done in slightly different circumstances. The liquids could be poured into a different shaped tray, or a tray made out of thicker plastic, or the liquids could be a different temperature. This would then give a larger range of results, by showing how the refractive index changes under different circumstances.

Mr Strange        Physics Coursework        

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