Class Group: S15 Lab Group’s No: 9 CENTRE OF FOUNDATION STUDIES FOUNDATION PHYSICS II LABORATORY REPORT Experiment Name Student ID Lab Instructor’s Name Date of Experiment REFLECTION & REFRACTION OF LIGHT SYED AMZAR BIN SYED MUSTAFA 2021201512 NOR FARIDAH HANIM BINTI MAT JUNIT 23RD FEBRUARY 2022 Member 1 SYED AMZAR BIN SYED MUSTAFA (2021201512) Member 2 SUMAYYAH BINTI LOKMAN (2021815144) Member 3 WAN NUR FHARISA BINTI WAN MOHAMAD ZANI (2021845722) Marks Comment PHY098 REFLECTION & REFRACTION OF LIGHT Syed Amzar Syed Mustafa Partners: Sumayyah Lokman, Wan Nur Fharisa Date Performed: February 23, 2022 Tutor’s/Lecturer’s Name: Nor Faridah Hanim Mat Junit ABSTRACT An experiment was performed to verify the law of reflection of light known as Snell’s law and to determine the refractive index of glass block. The refractive index of glass, n2 is determined by calculating the slope of graph sin θi versus sin θr which results in the value of 1.52. The refractive index of air, n1 is 1. INTRODUCTION The processes of reflection and refraction can occur when light moving in one medium hits a boundary then going into a second medium. In reflection, some of the light that strikes the second medium reflects and it is called reflection. Refraction occurs when light passing through the second medium bends at an angle to the normal to the boundary. Reflection that occurs on smooth surfaces will result in parallel to one another and it is called specular diffusion, while for the rough surface, it will reflect the rays in many directions. The incident and reflected rays make angles θi and θr with a line perpendicular to the surface at the point where the incident rays strike the surface which called as normal line. The reflection law’s states that angle of incidence θi is equal to the angle of reflection as shown below. θi = θr Refraction of light happens when a ray of light passing through a transparent medium meets up with a boundary leading to another transparent medium, part of the ray is reflected, and the other part enters the second medium. The light that enters the second medium is refracted when it bends at the boundary. At the point of incidence, the incident ray, reflected ray, refracted ray, and normal are all in the same plane. The law of refraction is known as Snell's law. The constant in Snell's law is the ratio of the refractive indices of the two materials n and n'. The law of refraction is usually written as below. n1sinθ1 = n2sinθ2 Thus, this experiment is conducted in order to verify the law of reflection of light and determine the refractive index of glass block by doing calculations. METHODOLOGY 1. Procedure for reflection of light experiment The mirror was placed on a sheet of paper, holding it vertically, and its outline was drawn. The ray box was set up such that a ray of light strikes the mirror. The incident and reflected rays were marked with crosses. The mirror was removed and marked the point of incidence. A ruler was used to join the crosses along the lines of the ray of light. The protractor was used to draw the normal at the point of incidence. Measure angle of incidence θi, and the angle of reflection θr. Steps 1-7 was repeated for five different angles of incidence using the same set up. 2. Procedure for refraction of light experiment The glass block was placed on a sheet of paper and its outline was drawn. The ray box was set up such that a ray of light enters the glass block from the longest side. The incident and the emergent rays were marked with crosses, and the point of incidence. The glass block was removed, and the ruler was used to join the crosses to draw the path of the ray of light. The protractor was used to draw the normal to the glass surface. Angle of incidence θi, and the angle of refraction θr were measured. Steps 1-6 was repeated for five other angles of incidence. RESULTS Table for reflection data Angle of incidences, θi (°) Angle of reflection, θr (°) 10 10 20 20 30 30 40 40 50 50 60 60 Table for refraction data Angle of incidences, θi (°) Angle of refraction, θr (°) n2 10 6.65 1.50 20 13.18 1.50 30 19.47 1.50 40 25.37 1.50 50 30.71 1.50 60 35.26 1.50 ANALYSIS PART 1 Graph of θi against θr 70 60 60 50 50 40 40 θi 30 30 20 20 10 10 0 0 10 20 30 40 50 60 θr PART 2 θi (°) θr (°) sinθi sinθr 10 6.65 0.17 0.12 20 13.18 0.34 0.23 30 19.47 0.50 0.33 40 25.37 0.64 0.43 50 30.71 0.77 0.51 60 35.26 0.87 0.58 70 Graph of sinθi against sinθr 1 0.87 0.9 0.77 0.8 0.64 0.7 sinθi 0.6 0.5 0.5 0.34 0.4 0.3 0.17 0.2 0.1 0 0 1 2 3 4 5 sinθr ANALYSIS (CALCULATION) • Calculation of n2 using Snell’s law formula n1sinθ1 = n2sinθ2 n2 = 𝑛1 sin 𝜃1 sin 𝜃2 (1.00)sin(10) = sin(6.65) • Example calculation of sinθi: sinθi = sin 10˚ sinθi = 0.17 • Example calculation of sinθr sinθr = sin 6.65 sinθr = 0.12 • Gradient of the graph Maximum gradient: 0.77−0.64 mmax = 0.51−0.43 = 1.63 Best line gradient: 0.87−0.17 m = 0.58−0.51 = 1.52 Minimum gradient: 0.64−0.50 mmin = 0.43−0.33 = 1.4 = 1.50 6 7 • Error of gradient Δm = • mmax −mmin 2 = 1.63−1.4 2 = 0.12 Refractive index, n 1.52± 0.12 • Percentage of precision of refractive index Δm m • 0.12 × 100% = 1.52 × 100% = 7.89% Accuracy of refractive index in medium by experiment % Accuracy = 𝑛𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡−𝑛𝑡ℎ𝑒𝑜𝑟𝑦 × 100% 𝑛𝑡ℎ𝑒𝑜𝑟𝑦 1.52−1.50 × 100% 1.50 = = 1.33% DISCUSSION PART 1 In part 1, a mirror is held vertically and placed on a sheet of paper. The incidence and reflected rays were marked on the paper when the light ray strikes the mirror. The angle of incidence, θi and angle of reflection, θr is measured using protractor. The steps are repeated for five different angles of incidence using the same apparatus set up. This experiment is conducted to verify the law of reflection. The law of reflection states that when the light ray reflects from a smooth surface, the reflected angle, θr is equal to the incidence angle, θi as shown in this equation, θi = θr. The reflective angles formed with respect to normal lines are equal to incidence angle when measured using protractor. When a graph of θi versus θr is plotted, a straight line is produced which is consistent with the law of reflection. Based on the graph, The incidence angles are equal to reflected angle for every incidence angle used. PART 2 In part 2, The glass block was placed on a sheet of paper and its outline was drawn. The incident and emergent angle are marked and angle of incidence, θi along with angle of reflection, θr is measured using protractor. The steps are repeated 5 times more using 5 different angles and same apparatus set up. In this experiment, Snell’s Law is used to determine the refractive index of the semicircular glass. When the light ray passes from less dense medium which has a smaller refractive index to denser medium, the ray will bend towards normal. In contrast, when the light ray passes from denser medium towards less dense medium, the light ray will bend away from normal. Using Snell’s Law formula which is n1sinθ1 = n2sinθ2, the refractive index of the glass block, n2 is calculated. The refractive index of air, n1 is constant which is 1. The refractive index obtained from the graph is 1.52 ± 0.12. A graph of sinθi against sinθr is plotted resulting in a straight line. The slope of the graph obtained indicates the refractive index of the glass block which is 1.52. It is slightly different from the actual refractive angle of the glass block which is 1.50. The result has 7.89% error. Errors made in this experiment may be caused by a lot of factors. For instance, inaccuracies when measuring the incidence angle which is categorized as random error. Other than that, the laser beam might not be aligned on the track. CONCLUSION In this experiment, the law of reflection is proven, and the refractive index of a glass block is determined using Snell’s law. The angle of reflection is always equal to angle of incidence while the angle of refraction differs depending on index of refraction on two mediums. REFERENCES  light - Reflection and refraction | Britannica. (n.d.). Encyclopedia Britannica. Retrieved March 2, 2022, from https://www.britannica.com/science/light/Reflection-and-refraction  Video details - clickview library of educational videos. ClickView UK. (2021, September 24). Retrieved March 2, 2022, from https://www.clickview.co.uk/curriculumlibraries/videodetails/id=31410460&cat=3708355&library=secondary#:~:text=A%20plane% 20mirror%20forms%20the,be%20equidistant%20from%20the%20mirror .  Austin, J. (2014, May 23). Experiments to illustrate the relationship between the behaviour of light rays interacting with optical elements. Academia.edu. Retrieved March 2, 2022, from https://www.academia.edu/6980598/Experiments_to_illustrate_the_relationship_between_the _behaviour_of_light_rays_interacting_with_optical_elements PRE-LAB QUESTIONS 1. State the law of reflection. Angle of incidence equals to angle of reflection. 2. Sketch a ray diagram of a plane mirror showing the incident ray, the reflected ray, and the normal lie on the same plane. 3. State the theoretical value of index of refraction, n of a glass. n= 1.50 4. Sketch a ray diagram of the refraction of light as it. (a) moves from air into glass. Air Glass ϴr ϴi (b) moves from glass into air. Glass Air ϴr ϴi 5. By plotting a graph of sinϴ1 versus sinϴ2, what is the physical quantity represented by the gradient of the graph? Gradient of the graph represents refractive index of the glass. POST LAB QUESTIONS 1. List properties of images formed by plane mirror. A plane mirror forms the image of an object by reflecting the light rays coming from the object that we used. The properties of image formed by plane mirrors are virtual, erect, and same size as the object and the image also equidistant from the mirror. 2. State the relationship between incident and reflection angle for plane mirror. Incident and reflection angle are the same for plane mirror. 3. Explain why the index of refraction is dimensionless and must be greater than or equal to 1. Index of refraction, n is dimensionless as it is a ratio of the speed of light in vacuum 𝑐 and in a certain material, n= 𝑣. The value must be greater than or equal to 1 because light travels the fastest in vacuum.