Light and calculate refractive Essays

Light and calculate refractive Essays Light and calculate refractive Essay Light and calculate refractive Essay In this experiment, a mechanism is prepared to observe the refraction of light and calculate refractive index of water according to the data taken from the experiment. Refraction means the bending of a wave resulting from a change in its velocity as its moves from one medium to another. Since the frequency of a wave cannot change, independent of the source changing its frequency when it originally emits a wave. This change in wave velocity must result from a change in its wavelength in the second medium. [1] As shown in the diagram, when the waves encounter an oblique interface, both their direction and wavelength change. In the instance illustrated, the wavelengths shorten and the reflected rays â€Å"bend toward the normal† as the wave enter the shallow or slower medium: To quantify the degree of refraction, a dimensionless quantity called index of refraction (n) is introduced. Since the refractive index (optical density) of air is equal to 1 (, refractine index of water is equal to sine of angle of light in medium of air ( over sine of angle of light in medium of water (. That’s why slope of the graph vs gives the approximate value of refractive index of water . Figure : Graph of vs Since is proportional to , the graph which is given above is linear. According to the graph above, slope of best fit line gives the experimental value of refractive index of water, slope of worst line with greatest slope gives the maximum value of refractive index of water and the worst line with least slope gives the minimum value of refractive index of water in this experiment. Uncertainty of refractive index of water : Percentage error calculations: CONCLUSION EVALUATION In this experiment, refractive index or in other words optical density of water ( is aimed to be found by the help of parallax method. When an ultrasonic wave passes through an interface between two materials at an oblique angle, and the materials have different indices of refraction, both reflected and refracted waves are produced. [3] It can be also told that when any wave strikes a boundary, some of the energy is reflected and some is transmitted or absorbed. [4] This also occurs with light, which is why objects seen across an interface appear to be shifted relative to where they really are. Because, when two or three dimensional wave travelling in one medium crosses a boundary into another medium, the transmitted wave may move in a different direction than the incident wave as shown in the figure below. This phenomenon is known as refraction. For example, if you look straight down at an object at the bottom of a glass of water, it looks closer than it really is. Another good way to visualize how light and sound refract is to shine a flashlight into a bowl of slightly cloudy water noting the refraction angle with respect to the incident angle. Figure : Refraction of wave passing a boundary Refraction takes place at an interface due to the different velocities of the acoustic waves within the two materials. The velocity of sound in each material is determined by the material properties like density for that material. In optics, the ration of the speed of light to the speed (v) in a material is called the index of refraction which is shown with â€Å"n†. Refractive index is also defined as; Snell’s law of refraction describes that when light passes from one transparent medium into another with a different index of refraction, part of the incident light is reflected at the boundary. The remainder passes into the new medium. If a ray of light is incident at an to the surface, the ray changes direction as it enters the new medium. This change in direction or bending is called refraction. Figure : Light refracted passing from air into water Figure above shows a ray passing from air into water. Angle ? 1 is the angle the incident ray makes with the y-axis which is perpendicular to the surface and that angle ? 1 is called the angle of incidence. Angle ? 2 is the angle that the refracted ray makes with y-axis and that angle is called angle of refraction. The angle of refraction depends on the speed of light in two media and the incident angle. Snell’s law declares that; (where n: refractive index of the medium) According to that equation is the angle of incidence and is the angle of refraction. It is clear from the equation above that if than, . This equation of Snell is also known as law of refraction. In the experiment, a straight line is drawn at the middle of the paper and upside of the line is marked as medium of water and downside is marked as medium of air. A transparent semicircular container is put in the part of the medium of water. At last needles are sanked into the paper as shown in the figure below and angles with y-axis are measured. Figure: Mechanism of the experiment In order to find the refractive index of water ( Snell’s law of refraction is used. In the equation refractive index of air ( is taken 1. 00. [5] By using the slope of the best fit line in the graph of vs , refractive index of water is found out to be 1. 331. Maximum value of refractive index is found 1. 400 with the worst line of maximum slope and minimum value is found 1. 251 with the worst line of minimum slope. Uncertainty of the measurement is 0. 074 with the formula of . Furthermore, in 0th trial angle between y-axis in both medium of water and air is 0 °. That means the angle between x-axis is 90 °. There is no refraction just because of the light is perpendicular to x-axis. During the percentage error calculations literary value of refractive index of water is taken 1. 334 (i. e 4/3). [6] So the percentage error is calculated with the formula of and it is found 0. 2 % which is really low error. Difference between expected value (1. 334) and experimental value (1. 331) is 0. 003. The results of the experiment is not different from the expected value of optical density of water. In the graph of vs , the best line passes through point â€Å"0†, that shows there is no systematic error in the experiment. In addition, best fit line of the graph passes through all error bars, that shows there is no random error as well. Furthermore, there are some limitation which affects the results of the investigation. Firstly, the amount of water in the semicircular container is very important. The container should be full of water and there shouldn’t be any empty place in the container. Because it can affect the observation of refraction in water. Thus, adding more water to the container to make observations better can make the observation more effective. Another error source can be the thickness of the semicircular transparent container. In this experiment refraction of light between two different media is observed. However, wall of the container is another medium. That’s why, the thinner the semicircular container is, the more effective the results are. So using a thinner transparent container can be a solution for that limitation. Moreover, using thinner container can be helpful for the observer who looks from the medium of air to see the needle. On the grounds that thinner wall of container makes the observations easier for the experimenter by creating a clear visual material. The temperature of water is an important factor which affects th results of the experiment. Because of that, refractive index values are usually determined at standard temperature. A higher temperature means the liqiud becomes less dense and less viscous, causing light to travel faster in the medium. This results in a smaller value for the refractive index due to a smaller ration. A lower temperature means the liquid becomes denser and has a higher viscosity, causing light to travel slower in the medium. This results in a larger value for the refractive index due to a larger ratio. In addition, refractometers which are laboratory or field devices for the measurement of an index of refraction usually takes measurement for standard temperature (298.15K/25 °C). That’s why, making experiment at standard temperature gives better results. Moreover, refractive index of vacuum which is a measurement of standard temperature is taken used during the calculations. Therefore, during the experiment paying attention to the temperature and trying to make it constant at 25 °C makes the results better. Another limitation is the thickness of the needles. Using thick needles can be misleading for the results of the experiment by affecting observations of refraction. So, thinner needles can solve that error source.