Light: Objects that Absorb, Transmit and/or Reflect Light
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- Common Misconceptions
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Background InformationPrior Knowledge:In this unit before starting these activities, students should have already learned: Some objects give off their own light and some require an external source of light to be seen Light travels away from a source in all directions Light travels in straight lines They may also know: Some history of manmade light Natural and artificial light are different Fireflies make light There are different colours of light Mixing two colours of light gives a third different colour Common Misconceptions:Light either passes through or does not pass through an object, it cannot do both Only mirrors or smooth shiny things reflect light We see things because light shines on them and brightens them, not because they reflect light to our eyes Light is instantaneous, it does not travel over a distance Did You Know?For a more in-depth understanding of light, there are two very good online resources. NSTA (National Science Teachers Association) has a variety of free resources. “Science Objects” are information packages about specific topics. Go to http://www.nsta.org. You may be required to register, however registration is free. Under Learning Resources and Opportunities click on Science Objects. There is a search box on the left. In this case, type “light”. There are four Science Objects related to light. The Physics Classroom found at http://www.physicsclassroom.com/Class/light/U12L2a.cfm talks about the electromagnetic spectrum, visible light and the eye, light absorption, transmission, and reflection and colours. Models for light With grade four students the ray model of light is used. You should be aware that there are actually three models of light that scientists find useful when thinking about and discussing light: the ray model the particle model the wave model Some properties of light are best described using rays, some using particles and some are best described using waves. None of the models by themselves, describe all of light’s properties. Information is given on each of the models to provide you with a better idea of how light acts, even though the particle and wave models will not be used with students at this level. The ray model is an excellent model for visualizing how light refracts and reflects. An object that gives off light sends “light rays” in straight lines in every direction until they hit something. If it is a mirror, the rays are reflected in a very specific and predictable way. The angle of the incoming light ray determines the angle of the outgoing light ray. Those angles are always equal. You may have heard “the angle of incidence (the incoming ray) is always equal to the angle of reflection (outgoing ray)”. This may be hard to see with a normal flashlight since the light rays are spread out. Lasers give a pretty accurate result. If you wanted to measure these angles, you could use a protractor. 
This is also true with curved mirrors. This site might help http://www.learner.org/teacherslab/science/light/lawslight/funhouse/index.html 
The Wave model is very useful when talking about the electromagnetic spectrum. This includes visible light, microwaves, x-rays plus a few others. Electromagnetic waves are similar to sound waves and water waves in that they have a wavelength (the distance between two adjacent peaks) and a frequency (how many waves pass a given point in a certain amount of time). The wavelengths of visible light are exactly that, visible to the human eye, while wavelengths that are shorter or longer are not visible but still able to be perceived given the right equipment such as x-ray film, a TV (signals sent by a remote control), or a cell phone tower. White light is made up of all the colours of the spectrum (ROYGBIV) and black is the complete absence of those colours. Every colour has a very specific wavelength or frequency. Depending on the wavelengths reflected, different objects appear as different colours. If a certain material absorbs every wavelength but red, the red is reflected making the object appear red. This also explains why some objects can be transparent, translucent or opaque. It depends on how many light waves are absorbed. The third model for light is the photon model and it is helpful in explaining fluorescence and phosphorescence. The idea is that everything is made up of atoms which contain protons, neutrons and electrons. Usually electrons have a certain amount of energy and stay in the same “energy level” of their atom. Sometimes, however, when energy is added, the electrons use that energy to jump to a higher “energy level”. A useful analogy would be having electrons on a beach in a lower energy level then getting an energy injection that allows them to jump up onto a cliff. When the electrons jump from the higher energy level back down to the lower energy level, they emit light (photons). Fluorescent light bulbs work this way. They contain a bit of mercury that gets excited when electricity is passed through. The mercury atoms, in turn, excite the electrons in the coating of the glass which glow as the electrons move back from the higher energy level to the lower energy level. Instructional Plan Access Prior KnowledgeHave students think about objects and materials that allow light to pass through and those that prevent light from passing through (block light). The list can be generated on 2 separate pieces of chart paper, or each item could be written on an index card and placed under the appropriate heading on a bulletin board. The lists shared as a group could also be recorded on your smart board.
Post student versions of curricular outcomes on chart paper (see page 28). Inform students that these outcomes will be addressed over the next portion of the unit. Point out to students which outcomes are being addressed in each activity. Directory: sites -> asd-e sites -> Nstructions for Acquiring Excess Equipment online, through the 1033 Program sites -> Memorandum of agreement asd-e -> Anglophone East School District asd-e -> Asd-e code of Conduct Preamble asd-e -> Arnold. H. McLeod Expectations asd-e -> October 2013 re: school closures dear Parents/Guardians asd-e -> A great way to improve reading and writing skills over the summer asd-e -> Scholarships – bursaries – awards asd-e -> Qes pssc meeting December 4th Minutes Present Download 0.94 Mb. Share with your friends:
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