Main topic: how does light behave?




НазваниеMain topic: how does light behave?
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Megan Kirkpatrick

October 9, 2009

Subject Matter Research Paper


MAIN TOPIC: HOW DOES LIGHT BEHAVE?


Big Ideas 1 and 2: Particle Theory of Light and Wave Theory of Light

Light is a very familiar, yet very mysterious, concept to students and adults alike. However, one question in particular has intrigued scientists for centuries: does light travel in waves or in particles? Dating back to the ancient Greeks, light has most commonly been thought of as a constant stream of particles too small or too fast for the eye to see. These particles are referred to as photons, as named by Albert Einstein in 1905 (Gibbons, 2003, p. 28A). High school physic’s teacher Eric Saltsman describes photons as, “tiny packets of light energy,” (N.D, p.1). Thus, if light were to consist of photons, it would behave, “as if it consists of discrete particles rather than infinitely variable waves,” (Bigelow, 1996, p. 1). On the other side of this debate is scientist Christian Huygen’s 17th century idea that light can act as a wave. Saltsman explains, “When light…bends slightly as it passes around a corner, it shows wavelike behavior. If it were a particle, it would not bend around a corner,” (N.D, p.1). According to Huygens and Thomas Young- a 19th century scientist who supported Huygen’s theory- these waves of lights have specific wavelengths and frequency.

After lifetimes of research on this wondering, scientists have proposed that light can act either as a particle or as a wave. Aptly, these respective theories are the Particle Theory of Light and the Wave Theory of Light. “[Light] can’t [act as] both because the models of waves and particles are very different. The way they behave when traveling and when passing through mediums is very different,” (Saltsman, N.D, p. 1). Essentially, scientists have not uncovered just one way that light definitely moves, and thus these two theories exist. This is a deeply complex concept that scientists acknowledge has no simplistic explanation is available.

Big Ideas 3 and 4: Reflection and Refraction of Light

As Donna Gibbons explains, “When photons of light hit a surface or an object, some are absorbed and some bounce back off again. The bouncing back of light is called reflection,” (2003, p. 28). Reflection inherently involves light changing direction, but light will move in different directions depending on the material of the reflective surface (Wenham, 2005, p. 272). For example, a rough, dull material will scatter light in all directions, while a smooth, flat, shiny surface will reflect light “at the same angle that light strikes the glass,” (Gibbons, 2003, p. 28). If light is reflected at the same angle that it hits the material’s surface, the picture the reflection offers will be received by one’s eye as sharp, clear, and accurate. Thus, with the exception of funhouse mirrors, most mirrors are made of smooth, flat, polished glass. For the same reason, wood tables and cement walls are not popularly used as mirrors (Gibbons, 2003, p. 28).

Meanwhile, refraction of light means that light “changes directions, or ‘bends,’ as it passes the boundary between one medium and another,” (Bigelow, 1996, p. 1). This occurs because, according to Wenham, light travels at different speeds through different mediums (2005, p. 264). This change of speed forces light out of its naturally straight lined path, causing what appears to the human eye as a bend in the light. For example, light slows down when going from less to more dense mediums, such as from air to water. In this case, light will refract towards a “normal” line, otherwise known as any line perpendicular to the surface. On the other hand, when going from a more to a less dense object, light speeds up, such as from glass to air. Opposed to the prior situation, in this circumstance light will reflect away from its “normal” line (Robertson, 2003, p. 7-8). Robertson goes on to explain that there exists a mathematical relationship “that describes exactly how much and in what direction light bends when it goes from one medium to another,” (2003, p.8).


Experiment 1: Particle Theory Model (Gibbons, 2003, p. 29)

Procedure: Roll a wet tennis ball on the floor toward a flat wall. Use a piece of brown butcher paper in order to have visual proof of the ball’s track. Roll the ball against the wall three times. After each roll, use a ruler to measure the angle the ball was rolled and the angle the balled rebounded.

Evidence: Angle of ball roll Angle of ball rebound

Trial 1: 34 34

Trial 2: 76 76

Trial 3: 44 44


Experiment 2: Refraction “Appearing Coin” Test (Gibbons, 2003, p. 33A)

Question: What happens to light as it passes at an angle from air to water?

Hypothesis: The light slows down, since water is denser, and the light will bend.

Procedure: STEP 1- Put a pencil or straw inside of a clear drinking glass. Fill glass 2/3 the way with water. Draw the top and side view of the cup.




STEP 2- Then put a penny in an opaque bowl, using masking tape to make sure it stays in one spot. Look at the bowl from an angle that does not allow you to see the penny. Keep your angle of vision completely still as a partner fills up the bowl with water. What do you see once the bowl is filled with water?




Contributions to Learning


These experiments contributed to my understanding of light behaviors mainly because it allowed me to visually and experientially witness the concepts. Though I grasped the ideas I read about, actually watching as the penny appeared, the straw bent, and the tennis ball reflected before my eyes proved my sources’ points that reflection and refraction truly do cause and affect humans’ vision. As a learner I have consistently struggled with science concepts and connections, but completing these experiments after researching each topic allowed for a new level of enlightenment on the behaviors of light. After considering these concepts in a this new manner, I’ve realized I never directly considered that, as Vicki Cobb says, “Shadows are evidence that light travels in straight lines. Because light travels in straight lines, you can’t see [fully] around corners,” (2005, p. 25). Any scientific facts along these lines have not, until now, registered in my mind as having any connection to what and how I see. I am in the same position as the many students who, “tend to develop theories about the world that are based on their own direct experiences and on everyday language. Thus to learn science, they must often acknowledge that their own theories…are incorrect, and they must accept new theories,” (Anderson, 1986, p. 6). With the help of these experiments, I have been able to accept new theories and further my learning and understanding on light. I can now with confidence think about the “bent” straw in my green water bottle above and declare, as William Robertson does in his book, “light rays bend, or change directions…whenever light travels from one substance to another,” (2003, p.7). I can then too assert that, “Refraction occurs because light travels at different speeds through different materials,” (Gibbons, 2003, p. 34). Overall, these experiments cemented in my mind the connections about light behavior that I had failed to previously make.


Children’s Misconceptions of Light



Children house a myriad of science misconceptions, particularly about the behaviors of light. As Charles Anderson explains in his study on students’ light misconceptions, “to learn science, [children] must often acknowledge that their own theories and the evidence of their sense are incorrect or incomplete, and they must accept new theories that depend on unobservable constructs. This is not easy, and many students come to regard science as difficult to learn,” (1986, p. 6) The most basic of these incorrect or incomplete theories is, “light is not conceived as moving from one point to another with a finite speed…light is associated only with a source and/or its instantaneous effects,” (Hapkiewicz, 1992, p. 1). For example, most children flip the light switch and believe the light immediately appears in all area; they do not realize the light travels in rays from the light bulb out into the room, eventually filling it up. Along these same lines, many children believe objects are only seen when light shines on the object, not recognizing that light is reflected off of the object, moves between the object and the human’s eye, and allows for sight. As Charles Anderson displays, about 60% of the students he interviewed proclaimed that light reflects off of mirrors, but none of those students believed light reflects off of other material. Those students who did realize that light reflects off of opaque objects did not perceive the significance of the information when related to how people see (1986, p. 20). Overall, this proves that although some children may comprehend arbitrary bits of knowledge on light behavior, generally no child comes into school with an understanding of the connections between light, reflection, and human vision. Anderson articulates in his study that most adults neglect the misconceptions of children as they attempt to teach science: “Thus teachers and science curriculum developers often work in ignorance of how their students are thinking,” (1986, p. 6). In order to ensure that students finish their education with a connected, thorough understanding of science, teachers must take student misconceptions into account.


Bibliography

Anderson, C. W., & Smith, E. L. (1986, January). Children’s conceptions of light and

color: Understanding the roles of unseen rays (Rep. No. 166). Retrieved from The Institute for Research on Teaching, Michigan State University website: http://www.eric.ed.gov/

Bigelow, K. (1996). The fundamentals of optics. Retrieved from http://www.play- hookey.com/optics/

Cobb, Vicki. (2005). Light action!: Amazing experiments with optics. The United States of America: The Society of Photo-Optical Instrumentation Engineers.

Gibbons, D., Mayer, S., & Mintmier, J. (2003). Light and sound unit. State College, PA:

State College Area School District

Hapkiewicz, A. (1992). Finding a List of Science Misconceptions. MSTA Newsletter,

38(Winter’92), pp.11-14

Harmsworth, A. P. (2005). GCSE physics: waves. Retrieved from

http://www.gcse.com/waves.htm

Newton’s particle theory of light. (2004). Retrieved from University of Virginia’s website:http://galileo.phys.virginia.edu/classes/609.ral5q.fall04/LecturePDF/

L20-LIGHTII.pdf.

Operation Physics. (1998, September). Children's misconceptions about science. Retrieved from http://www.amasci.com/miscon/opphys.html

Robertson, W. C., Ph. D. (2003). Stop faking it! : Finally understanding science so you can teach it. Arlington, Virginia: National Science Teacher Association.

Saltsman, E. (n.d.). Light: wave or particle? Retrieved from http://www.geocities.com/ CapeCanaveral/7997/light.html

Wenham, M. (2005). Understanding primary science. Los Angeles, California: Sage.


Wiggins, A. W. (2007). The joy of physics. Amherst, New York: Prometheus

Books.

Windschitl, M. (2005, October 7). Learning and teaching science as inquiry: A case study of elementary school teachers’ investigations of light. Science Education, 89(6), 1007-1042. Retrieved from http://www.eric.ed.gov/

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