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Drexel SDP GK 12 ACTIVITY Subject areas Unit title physical science Astronomy Holt Astronomy activities Activity title Grade level Reflection and refraction Holt Chapter 1 6 Time required 60 minutes Keywords reflection refraction light Educational standards 3 4 7D Portions of this lesson plan were permissibly adapted from Joshua Faber http w3 physics uiuc edu jfaber optics1 html Concept Vocabulary In this activity students investigate the behavior of light as it passes from one transparent medium air to another water They will use and investigate the concepts of reflection and refraction by studying the behavior of light as it travels through the air and through a tank of water They will also use the Holt text and other resources to review the astronomy terms telescope refraction refracting telescope reflecting telescope electromagnetic spectrum Students will exercise geometric concepts of angles and symmetry They will practice measurement skills using sketches and protractors Objectives Students will learn and understand how light can be reflected and refracted This activity will aid in the understanding of how light behaves in reflecting and refracting telescopes INSTRUCTIONAL STRATEGIES Group size This activity can be performed in groups of 4 6 students Duration It can be performed in one class period Before Students will perform the Motivate Activity on page 8 of the Holt Astronomy Teacher Edition text They will construct a water drop lens They should learn how light traveling through a lens can be used to magnify an image During A small rectangular fish tank or other similar small clear enclosure should be set on top of white sheets of paper The paper should extend out beyond the tank on all sides The instructor should fill the tank with water Students will be asked what will happen to light if we shine a flashlight onto the surface They should be encouraged to briefly discuss within groups the direction or directions the light will travel One student from each group should stand on one side of the aquarium and shine a flashlight on the surface The other members of the team should stand on the other side of the tank and note that some of the light is reflected at the water s surface Students should learn that when we see light upon the surface it is an indication that reflection is taking place some of the light is hitting the surface and bouncing into our eyes The students should now be asked if all the light is reflected from the surface They should be able to determine that some of the light is traveling down through the water It may help if students place their hands under the water to see that some of the light is indeed passing down through the liquid The light should also be visible on the white paper sitting beneath the tank Students should understand that transparent materials like water and glass can both reflect light and transmit light Ask them to think about another example of this concept i e seeing your reflection in transparent window glass Next students should place a yardstick within the water Students should look at the yardstick from a number of different angles and note how it appears to bend at the point where it enters the water Students should attempt to make a few accurate sketches of the bending they observe They can use protractors to estimate the bending angle in these drawings If a digital camera and printer are available it may be instructive to take photos of the ruler from various points and have the students measure the angle on printouts Students should be asked to think about whether the yardstick is truly bending when it enters the water Encourage the groups to feel the ruler as it enters the water to demonstrate that the yardstick remains straight despite its bent appearance Remind the students that we see the yardstick because light reflects from it and enters our eyes Once they have verified that the ruler does not physically bend in the water ask them to consider what might be bending instead Students should identify that the light itself bends as it travels from air to water Introduce them to the term refraction the process in which light changes speed and direction when it passes between different transparent media i e glass air water Ask the students to offer examples of refracted light they have encountered such as the apparent bending of a straw in a glass or the optical illusion of shallow water in a deep swimming pool Finally students will use a laser pointer to follow a path of light through the aquarium Students should be reminded that lasers are not to be shined in one another s eyes In order to make the laser beam visible in the water it will be necessary to add a small amount of milk Depending on the amount of water present it may only be necessary to add a few drops of milk If too much milk is added it will not be Portions of this lesson plan were permissibly adapted from Joshua Faber http w3 physics uiuc edu jfaber optics1 html able to travel through the tank Ask the students to think about why the milk allows us to see the laser beam Encourage them to consider the fact that the laser traveling through clear water travels in a straight line until it reaches the other side of the tank However by adding milk which contains small globules of proteins and fats the water becomes cloudier The small particles within the milk cause the light to scatter away from its straight path and some of those scattered beams find their way into our eyes allowing us to see the laser light Draw a parallel to other phenomenon in the natural world where light is scattered by small particles Ask the students to consider what makes beams of light visible in fog or mist They should learn and understand that small droplets of water condensing in the air will scatter light and make light beams visible Have the students try shining the lasers from various directions and at various angles First ask the students to shine the laser straight through from the front of the tank to a wall or sheet of paper behind the tank Then they should direct the light through the front of the tank at an angle so that it re emerges from one of the sides Finally can they shine the light through the front of the tank hitting one of the side walls and bouncing out the back These various angles are shown in the top down view here Finally students should construct a rudimentary telescope following the instructions of a basic kit such as the Anchor Optics kit B26057 They

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