Question: Reflection Refraction opaque objects that are ...

1 Grade 8 Science Module 4, Lesson 3 23 Vocabulary transparent opaque Reflection Law ofReflection light ray incident ray reflected ray normal angle ofincidence angle ofreflection Refraction Laws ofRefractionLesson 3 Reflection and RefractionLearning OutcomesAfter completing this lesson you will be able to explain the laws of Reflection identify examples of Reflection in daily life compare the Refraction of light through substances of differentdensities explain how Reflection and Refraction produce naturalphenomenaHow Does light Interact with objects ?At the beginning of this unit, when you were brainstorming whatyou knew about light , you may have included some of the waysthat light interacts with objects . In Grade 4 you learned thatobjects can be classifiedas transparent(let light pass through)or opaque (don't let light pass through).

2 In this section you'llexamine in more detail what happens when light interacts withopaque objects that are reflective in nature, and also withtransparent : ReflectionThere are many instances where areflectioncan be observed ineveryday life, for example, your face in a bathroom mirror. Whatare other examples of where you might encounter your reflectionover the course of a day? Give two or three Module 4,Lesson 3 Grade 8 ScienceHowDoes LightReflect?*How does a ball bounce back to you after you throw it against awall? It depends how you throw it. If you throw the ball straight,itwill bounce back straight. If you throw it at an angle, it willbounce back at an , you know, can bounce. "Bounced" light is reflected can predict how reflected light will behave.

3 Just follow single beam of light is called alightray. light is made up ofmany, many light rays. But let us look at one light / reflectedray raymirrorThis is a single light ray. It is hitting a flat mirror at an it is bouncing off. It is ray that hits the mirror is called the incident ray that bounces off the mirror is called the reflected ray. Now let's draw a line that makes a right angle (90 degrees)where the incident ray hits the mirror. This line is called / reflectedray ray3(0 angle of 7\-30 angle ofincidence Reflection ,aandGrade 8 ScienceModule 4, Lesson 3 25 Practice: How Does light Reflect?Two reflecting rays are shown in Figures A and B. Identify theparts shown by number. Choose from the following:normalangle of incidenceangle of reflectionWrite youranswers next to the correct AFigure the Law of of the angles above are equal?)

4 (Use nincident rayreflected raya26 . Module 4,Lesson 3 Grade8 ScienceWhat is Refraction ?* light travels in straight lines. But light rays can also "bend."They can_change have seen that light changes direction when it is also changes direction when it passes at an angle from onemedium into another medium. This bending is called causes us to see objects at positions different fromtheir actual positions. You may have experienced Refraction . Didyou ever reach into a fish tank to pick up a rock? Was the rockexactly where you thought it was?How can Refraction be explained? light travels at different speeds through different travels at about 300,000 kilometers (186,000 miles) persecond in air. But light slows down in other substances.)

5 Inwater, for example, light slows down to about 225,000 kilometers(140,000 miles) per speed at which light travels through a medium dependsupon the density of that medium. Density has to do with howclosely packed the molecules of a substance are. The more closelypacked the molecules are, the more dense the substance substances have different densities. For example,water is more dense than following are the Laws of Refraction . They explain howlight ) light that moves at an angle froma less dense medium to a moredense medium bends toward 8 ScienceModule 4, Lesson 3 27 Practice: What is Refraction ? light rayw normal your own experience,you know thatglass isdense than , less2. In Figure A, light is passingfromglassto air, airto glassLiglassFiguxe light is hitting the glassat an angle,straight light bending.

6 It being , is not is, is isn't the light being refracted? the part of the Law of Refraction that explains whythis is at Figures B through G. In each, light is being dotted line in colour is the normal. Is the light beingrefracted toward the normal or away from the normal? Completethe sentence under each Module 4, Lesson 3 Grade 8 ScienceNow, answer with complete FFigure : What's Happening?Look at Figures H and I. Answer the questions with In Figure H, light ispassing fromFigure Hglass to air, air to glassb. Glass is densemore, lessthan light is hitting the glassat an angle, straight light bending. It being , is not is, is light is being refracted the , away the part of the Law of Refraction that explains whythis is 8 Science Module 4, Lesson light is hitting the glassat an angle, straight light bending.

7 It being , is not is, is light is being refracted the , away the part of the Law of Refraction that explains whythis is : Refraction and Change of PositionStudy Figure J. Answer the Jactually at C. But to tlhe fish appears to be atkd1,30 Module 4, Lesson 3 Grade 8 boy sees the fish in line with the refracted light . Therefracted light isA, The boy sees the fish than it really away,closerb. The boy also sees the fish in the waterthan it really is. higher, seem. to change the position of Edoes, does notNatural light PhenomenaSeveral natural phenomena are created by the Reflection and/orrefraction of light . These include everything from our blue sky tosunsets, sundogs, rainbows, mirages, and perhaps the mostimpressive-northern lights.

8 The following articles describe someof these phenomena. Read the articles and complete the questionsthat appear after *In a rainbow, raindrops in the air act as tiny prisms. light entersthe drop, reflects off the side of the drop and exits, and in theprocess is broken into a spectrum just like it is in a triangularglass prism. Like this:DI >Grade 8 Science Module 4, Lesson 331 The angle between the ray of light coming in and the red raycoming out of the drops is 42 degrees for red, and 40 degrees forviolet. You can see in this diagram that the angles causedifferent colours from different drops to, reach your eye, forminga circular rim of colour in the sky-a rainbow! In a doublerainbow, the second bow is produced because droplets can havetwo reflections internally and get the same effect.

9 The dropletshave to be the right size to get two reflections to Is the Sky Blue?Here is something interesting to think about. When you look atthe sky at night it is black, with the stars and the moon formingpoints of light on that black background. So why is it that ,during the day, the sky does not remain black with the sunacting as another point of light ? Why does the daytime sky turna bright blue and the stars disappear?The first thing to recognize is that the sun is an extremely brightsource of light -much brighter than the moon. The second thingto recognize is that the atoms of nitrogen and oxygen in theatmosphere have an effect on the sunlight that passes throughthem. There is a physical phenomenon called "Rayleighscattering" that causes light to scatter when it passes throughparticles that have a diameter 1/10th of that of the wavelength(colour) of the light .

10 Sunlight is made up of all different coloursof light , but because of the elements in the atmosphere, thecolour blue is scattered much more efficiently than other when you look at the sky on a clear day, you can see the sunas a bright disk. The blueness you see everywhere else is all ofthe atoms in the atmosphere scattering blue light toward you(but not scattering red light , yellow light , green light , etc., nearlyas well).32 Module 4, Lesson 3 Grade 8 Sciencefaces flat, parallel to the ground. An observer may pass throughthe same plane as many of the falling ice crystals near sunrise orsunset. During this alignment, each crystal can act like aminiature lens, refracting sunlight into our view and creatingparhelia,the technical term for : Natural light phenomenon is created by the Refraction of light andwhat medium causes the Refraction ?