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To find out the factors affecting the refractive index of liquid by using different temperature and concentration of salt solutions, glucose solutions, sucrose solutions and corn oil.

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Introduction

Factors affecting the refractive index of liquid Aim To find out the factors affecting the refractive index of liquid by using different temperature and concentration of salt solutions, glucose solutions, sucrose solutions and corn oil. Research and rationale Before doing this investigation, I have a few choices of topics, including properties of condom, centripetal force of a four wheel drive toy car, and refractive index. I started researching through the Internet. I have come across a web site called 'Brother Gregory investigate', 1 concerning measurement of refractive index. I found this experiment very interesting, using simple and easily available instruments and appropriate for A-level standard. I found that refractometry is very useful in measuring sweetness in food industry.2 The experiment in the web site is using glass, in order to make more variations, I choose to use salt and sugar solutions. Moreover, the refractive index of some liquids is already known, so that I can have a basic idea of how accurate are my results. Here are some of the basic principles about refractive index found from some web sites and books. Physics principle Refraction is the process that takes place when light travels from one medium to another with a different optical density and its path bends. Refractive index of a medium means the magnitude of refraction as light travels through the medium. The higher the value of refractive index means the light bends more as it travels through the medium. The amount the light bends is dependent upon the velocity of light in the medium. The speed of light decreases in the denser medium.3 If the refractive index is 1, which means it travels through the medium in a straight line, the angle of incidence (i) is equal to the angle of refraction (r). Based on Snell's law, the basic formula for measuring the refractive index is: Where � is the refractive index of the medium. ...read more.

Middle

So I change the container to a 12 cm (depth) x 15 cm x 12 cm size to ensure that the angle of incidence is bigger. - 200 ml of solution is very little, the depth is only about 1mm, so I have to use a lot more liquid, to reach the depth of 8.6cm, which is about 3000 ml. If I use a smaller container, I need only 1400 ml to maintain a reasonable depth. Therefore I can use less liquid for a smaller container for saving of resources. - The light beam will run out of batteries easily, however I cannot move the light source to change batteries once it is fixed. I have made a battery pack and connect it with the light source by electric wires, since the batteries are now AA batteries they can stay on for a lot longer time. The batteries are now external and I can change batteries easily. There is a switch at the battery pack, I can turn the power on and off without moving the light source (see photo 1 in the next page). - The initial method is not accurate since there can be refraction when light travel through the bottom of the container. To improve accuracy, instead of putting the container on the rack and mark on the A4 paper, I stick a ruler with silicon adhesive at the inside of the bottom of the container, before I put the solution into the container I set the light beam to a position where it shone exactly on the point '0' on the ruler. I do not need the paper anymore since I can read the distance L1 from above the container (see photo 2). - It is very difficult to measure the value of L2 and x, since the point where the light beam enters the solution is not shown on the solution surface. ...read more.

Conclusion

If the two anomalous results is compare to the 5% uncertainty they are still acceptable. However, this investigation does not prove my fourth hypothesis that the refractive index decrease as the temperature increase. From the research from the Internet, there are some changes for the refractive index with the temperature, but very small 4. For example, the difference in refractive index of water at 50 degree Celsius and 60 degree celsius is only 0.001. It may require a scientific refractometer like an Abbe refractometer 2 to detect a tiny change. Instead of increasing the temperature, I may need to decrease the temperature to below the melting point, so that the solution changed from liquid state to solid state and see whether the refractive index increase. One drawback of using oil is, the concentration of oil is 100%, I cannot compare it with the other results, since it cannot be diluted by water and I have difficulty looking for other solvents to dilute oil. Besides using oil I can use some other solutions such as ethanol, sulphuric acid, acetic acid, etc. Further investigation can be done using different wavelength of light. I have tried to look for a light source providing blue monochromatic light beam. I predicted that the reflective index would be different if I use another light source of different colour since they are having different wavelength. However blue monochromatic light source is no commercially available. Conclusion This investigation proves that various factors affect the refractive index of liquid. They include different concentrations and different types of liquid. The temperature of the solution does not change the refractive index in same state. My results are fairly accurate; all the results are within the uncertainty limit. Although this experiment looks simple and easy to conduct, actually it requires very precise skills, since one millimetre difference can change the refractive index to about 0.05, which is a great change. The principle of this investigation is very useful in food industry like Abbe Refractometer. It can be used for determining the sucrose content of food. I found this investigation very challenging and interesting. ...read more.

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