REFLECTIONIda Lyn A. Azuelo BSED Physics 3

• involves two rays• Specular and Diffuse• “Law of Reflection”

REFLECTION

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LAW OF REFLECTION When light falls on a

surface which is plane, the angle with which the light falls on the surface is equal to the angle with which the light reflects back and the incident ray, reflected ray and the normal ray lies in the same plane.

Reflection

All the light travelling in one direction and reflecting from the mirror is reflected in one direction.

Smooth, shiny surfaces

The rays incident at slightly different points on the surface are reflected in completely different directions.

Rough, dull surfaces

Specular Reflection Diffuse Reflection

Specular Reflection

Specular Reflection

Which part of the figures (a) or (b), better shows specular reflection of light from the roadway?

(a) (b)

Diffuse Reflection

Applying Physics

An observer on the west-facing beach of a large lake is watching the beginning of a sunset. The water is very smooth except for some areas with small ripples. The observer notices that some areas of the water are blue and some are pink. Why does the water appear to be different colors in different areas?

Explanation The different colors arise from specular and

diffuse reflection. The smooth areas of the water will specularly reflect the light from the west, which is the pink light from the sunset. The areas with small ripples will reflect the light diffusely, so light from all parts of the sky will be reflected into the observer’s eyes. Because most of the sky is still blue at the beginning of the sunset, these areas will appear to be blue.

The light reflects off in all directions because of the irregularities on the surface of an object that are larger than the wavelength of light but it does not mean that the law of reflected is flouted. All objects obey the law of reflection on a microscopic level. This means that at different points on the surface, the normal is different. The angle of reflection is still equal to the angle of incidence at that point and the normal is unique at that point in the surface.

NAIVE CONCEPTION (corrected version)

Test.

1. Specular or Diffuse Reflection?

Plane mirror

θI θR

IR

Test.

1. Specular or Diffuse Reflection?

I

R

Keep in mind that the diagrams are made to view in a microscopic outlook of an object on the atomic level. There are billions of light rays and billions of surfaces. So while seeing things, a lot of the light is diffused. That's why when a person looks at something, even if it is not directly faced into the sun, the person still get enough light to see it.

NAIVE CONCEPTION (corrected version)

In diffused reflection light scatters away then people must not be able to see it. So, how are people seeing any things in the world?

References (1999, July 27). Retrieved December 6, 2014, from The reflection and

refraction of light: http://physics.bu.edu/~duffy/PY106/Reflection.html Doris Jeanne Wagner and Rensselaer Polytechnic Institute. (2004).

Retrieved December 6, 2014, from Sample Problems for The Law of Reflection: http://www.rpi.edu/dept/phys/ScIT/InformationTransfer/reflrefr/rr_sample/rrsample_05.html

Elert, G. (2010). Reflection. Retrieved December 6, 2014, from The Physics Hypertextbook: http://physics.info/reflection/

Fitzpatrick, R. (2007, July 7). Law of Reflection. Retrieved December 6, 2014, from http://farside.ph.utexas.edu/teaching/302l/lectures/node127.html

Freudenrich, P. C. (2001, March 6). How Fiber Optics Work. Retrieved December 6, 2014, from HowStuffWorks.com: http://computer.howstuffworks.com/fiber-optic.htm

Geometric Optics. (2014). Retrieved December 6, 2014, from SparkNotes: http://www.sparknotes.com/physics/optics/geom/problems.html

References Law of Reflection. (2014). Retrieved December 6, 2014, from

TutorVista.com: http://physics.tutorvista.com/light/law-of-reflection.html Lesson 26: Reflection & Mirror Diagrams. (2013, July 11). Retrieved

December 6, 2014, from studyphysics.ca: http://www.studyphysics.ca/2007/30/07_emr/26_reflection_mirror.pdf

Optics 4 Kids. (2014). Retrieved December 6, 2014, from The Reflection of Light: http://www.optics4kids.org/home/content/what-is-optics/reflection/the-reflection-of-light.html

Serway, R. A., & Jewett, J. W. (2014). Physics for Scientists and Engineers with Modern Physics Ninth Edition. Boston: Brooks/Cole.

Serway, R. A., Vuille, C., & Faughn, J. S. (2009). College Physics Eighth Edition. California: Brooks Cole.

Specular and diffuse reflection 2. (2014, May 8). Retrieved December 6, 2014, from Khan Academy : https://www.khanacademy.org/test-prep/mcat/physical-processes/reflection-and-refraction/v/specular-and-diffues-reflection

References The Law of Reflection. (1996-2014). Retrieved December 6, 2014, from the

Physics Classroom: http://www.physicsclassroom.com/Class/refln/u13l1c.cfm

Total Internal Reflection. (2010, December 9). Retrieved December 6, 2014, from Youtube: Khan Academy: https://www.youtube.com/watch?v=WRuatAcd2WY

Total internal reflection. (2014, May 8). Retrieved December 6, 2014, from Khan Academy: https://www.khanacademy.org/test-prep/mcat/physical-processes/reflection-and-refraction/v/total-internal-reflection

Weisstein, E. W. (2007). Law of Reflection. Retrieved December 6, 2014, from Eric Weisstein's World of Physics: http://scienceworld.wolfram.com/physics/LawofReflection.html

THANK YOU!

REFLECTIONIda Lyn A. Azuelo BSED Physics 3