The Law of Reflection and Refraction Magno, Jana Raiza S. INPHYS2 A51
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Abstract - The experiment examined the difference between Law of Reflection and Law of Refraction and to further understand the basic principles through observation. For the reflection experiment, the results showed that it followed both parts of the law of reflection. For the refraction experiment, the results showed that it followed Snell’s law of refraction due to a direct relationship between the angle of incidence and angle of refraction. Based on these results, these results exhibited consistency with the theories governing the two different phenomena. I. INTRODUCTION The light travels at 3.00x108 m/s in a vacuum. Reflection indicates how light propagates through space on a straight line. The first law of reflection states that when the incident ray hit a smooth plane surface, creating an angle called the incidence angle, it will lie on the same plane as the normal line and its reflected ray. Thus, the second law of reflection states that the angle of incidence and the angle of reflection, the angle created by the reflected ray, is equal [1].
Fig 1. The law of reflection On the other hand, Refraction presents how light does not travel in a vacuum and at a different velocity. When light travels at a different velocity, it does not follow a straight line and therefore, it bends due to change in direction. This is commonly known as Snell’s Law.
Fig 2. The law of refraction This phenomenon occurs between two different mediums due to differences in index of refraction. The velocity of absorbed light is less than before it entered the second medium; thus, the denser the medium, the slower the light travels. This is governed by the equation:
𝑛 =
$ %
where: n = index of refraction v = velocity of the medium C = speed of light in a vacuum Thus, the main objective of the experiment is to examine the difference between Law of Reflection and Law of Refraction in its simplest form. Also, it is expected to understand the basic principles better through observation. II. METHODOLOGY The materials used were optics bench as the light source, a ray table and base-component holder, slit plate, and slit mask. The single ray of light was aligned to the normal line on the ray table. Ray optics mirror was used as the source of reflected ray while cylindrical lens was used as the source of refracted ray. The flat surface was aligned with the line labelled as “component” on the ray table. The ray table was rotated corresponding to the angle of incidence in order to measure the angle of reflection (or refraction) with respect to the normal line surface. This was repeated with the incident ray from the opposite side of normal.
60° 70° 80° 90°
Fig 4. Reflection equipment set-up [2]
35° 40° 43° 90°
37° 40° 43° 90°
The results showed two different angles of refraction between trials 1 and 2. This can be attributed due to the wide scope of the refracted light which could touch two different degrees at the same time. It may also have been because the lens was not properly placed that it did not form a perpendicular angle to the incident ray when hitting the normal surface [3]. As the ray table was rotated, the refracted ray becomes bent due to the curved surface of the lens which creates an angle that is unparalleled to the incident ray.
III. RESULTS AND DISCUSSION TABLE I REFLECTION USING A RAY OPTICS MIRROR Angle of incidence 0° 10° 20° 30° 40° 50° 60° 70° 80° 90°
Reflection1
Refelction2
0° 10° 20° 30° 40° 50° 60° 70° 80° 90°
0° 10° 20° 30° 40° 50° 60° 70° 80° 90°
The results showed that in both trials 1 and 2, the angle of incidence was equal to the angle of reflection. This is in accordance with the Law of Reflection where in any reflected ray of light upon a plane surface, the angle of incidence and angle of reflection must be equal. Another part of the Law of Reflection which states that the incident ray, the reflected ray, and the normally all lie on the same plane were shown in the experiment by first, aligning the single ray of light on the normal line, and observing both incident and reflected ray on the ray table. TABLE II REFRACTION USING A CYLINDRICAL LENS Angle of incidence 0° 10° 20° 30° 40° 50°
Refraction1
Refraction2
0° 6° 13° 19° 25° 30°
0° 8° 14° 20° 26° 32°
5
y = 0.8309x + 0.0607 0 -2 R² = 0.461790 -5
2
4
Angle of refraction
Fig. 6 Angle of Refraction1 Refraction2 Angle of incidence
Fig. 5 Refraction equipment set-up [2]
Angle of incidence
Refraction1
5
y = 0.5165x -00.2025 -2 R² = 0.216870 -5
2
4
Angle of refraction
Fig. 7 Angle of Refraction2 Both graphs are consistent with the Law of Refraction since there is a direct relationship between the angle of incidence and angle of refraction as indicated in Snell’s Law. IV. CONCLUSION Based on the aforementioned results, the experiment showed the principles behind the law of reflection and law of refraction. The data gathered exhibited consistency with the theories governing the two different phenomena. Therefore, the objectives of the experiment were achieved. Personal errors committed during the experiment can be obliterated by setting the equipment properly and reading the measurements properly. V. REFERENCES [1] Wettergreen, Margaret. “Lab 9 – Reflection, Refraction and Total Internal Reflection.” Accessed January 15, 2017.
http://www.academia.edu/9357508/Lab_9__Reflection_Refraction_and_Total_Internal_R eflection [2] De La Salle University. “Physics Laboratory 2 (compiled experiments in Heat, Electricity & Magnetism, Optics).” Accessed January 13, 2017. http://www.dlsu.edu.ph/academics/colleges/co s/physics/experiments.asp [3] Ruiz, Burhan. “Refraction Rays of Cylindrical Lens.” Accessed January 15, 2017. https://www.scribd.com/doc/134033346/Refra ction-Rays-of-Cylindrical-Lenses
