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# Ray Model of Light

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Slide that I created to support teaching science to my lower secondary student (Grade 7). The topic is Ray Model of Light. Some contents (pics and videos) are not mine. Hope it is useful for all teacher around the globe.

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### Ray Model of Light

1. 1. By Suta Pinatih Secondary Level Science 2014 Ray Model of Light
2. 2. What is light? How does it travel? What happened when light is blocked? Why do the leaves look green in the day and almost black when there‟s no light?
3. 3. Where does light come from?
4. 4. Sun is our major light source!
5. 5.  If there‟s no light, we would be in the darkness.  Light is form of energy. It has no mass and cannot be stored in a container.  Light travels in a straight lines unless changes what it travels through.  Light travels through matter: gases (air), liquids (water) and solid (glass).  Sunlight travels a distance of 150 million kilometres before reaching the earth. Facts about lights
6. 6. Are these light sources? Moon Water Mirror No, they aren‟t light sources. Because those objects do not emit light from itself but they reflect off the light from other light sources.
7. 7. How do we see? See the interactive content
8. 8. Rays  A thin line of light coming from a source is called a light ray.
9. 9. Beams  A bundle of light rays is called a beam of light. A beam of light can be parallel, divergent or convergent.
10. 10. How does light travel? • Light rays travel in straight lines from the light source. • When it hits an opaque object, some light is absorbed and the rest reflects off. • If the object is transparent, light rays pass through it easily. • If the object is translucent, some light can pass through, but the rest of the light will be reflected. light source
11. 11. CLEAR=TRANSPARENT SMOKY=TRANSLUCENT SOLID=OPAQUE
12. 12. How are shadows formed?  Light rays travel in straight lines, radiating out from the light source.  If rays are blocked by an opaque object a shadow forms where the light cannot reach.  If the light source is moved closer to the object, more light is blocked and a larger shadow is formed. light source light source
13. 13. How does sunlight cause shadows? 6am 8am 9am 12am 2pm 10am 3pm 4pm 7pm Looking North, the Sun appears to rise in the East... ...and travel across the sky until it sets in the West. The position of the Sun effects the position and length of the shadows created. Thanks to this natural phenomenon a sundial is able to tell us the time, as long as it is a sunny day!
14. 14. Phases of the moon.
15. 15. Mid-autumn festival is celebrated on the 15th of the 8th month in the Chinese calendar (full moon).
16. 16. Hari Raya Idulfitri is celebrated at the end of Ramadan, marked by the appearance of new moon on the last evening of Ramadan.
17. 17. Solar eclipse The moon blocks the light from the sun An observer on the earth will experience total darkness The shadow of the moon is formed on the earth.
18. 18. Key Ideas 1. Light travels in a straight lines. 2. In the ray model of light, straight lines with arrows are drawn to represent the path of light rays. 3. Shadows are formed when light is blocked by an opaque object.
19. 19. Reflection of Light
20. 20. How the light is reflected? i= angle of incidence r = angle of reflection normal Flat mirror  The incident ray, reflected ray and the normal at the point of incidence all lie in the same plane.  The „angle of reflection‟ is always equal to the „angel of incidence‟ (i = r).
21. 21. The texture of the surface affects the type of reflection that occurs at the surface. regular reflection (Specular) irregular reflection (Difuse)
22. 22. Have ever cut your hair in barbershop?
23. 23. Plane mirror b a The images formed by a plane mirror are upright, same size (undistorted), virtual and laterally inverted.
24. 24. Plane mirror dance studio room looks larger
25. 25. Periscope Periscope is used to change the direction of light by reflection.
26. 26. Concave mirror  The shape bends inwards.  The images formed by concave mirror are virtual and magnified if the object is put near the mirror.
27. 27. The uses of concave mirror
28. 28. Concave Mirror used in Reflecting Telescope http://www.bro.lsu.edu/telescope/Classroom/2.How%20Telescopes%20Work/Reflecting.gif
29. 29. Concentrate Solar Power on Youtube
30. 30. Convex mirror  The shape bends outwards.  Cover wider field of vision.  The images formed by convex mirror are upright, distorted, laterally inverted and smaller than the object.
31. 31. The uses of convex mirror
32. 32. The word “AMBULANCE” is written laterally inverted at the front of an ambulance. Source: http://brighteststar.org.uk/wp-content/uploads/2013/02/hi-res-ambulance.jpg
33. 33. Key Ideas 1. Reflection is the bouncing of light off the surface. Regular reflection occurs at the smooth surface while irregular reflection occurs at rough surface. 2. We use the ray model of light to represent the path taken by light as it is reflected off a surface. 3. Plane mirror has flat surface. The image formed is upright, laterally inverted, virtual and the same size as the object. 4. A concave mirror has a surface that bends inwards. The image formed is virtual and magnified. 5. A convex mirror has a surface that bends outwards. The image formed is upright, distorted and smaller. 6. Different types of reflecting surfaces are used for different purposes.
34. 34. Concave & Convex Mirror https://www.youtube.com/watch?v=jtTBOMVMSYM Workbook Vol A Worksheet 9.1
35. 35. Refraction Refraction is the bending of light as it travels from one medium to another medium of different density. A B glass block
36. 36. Refraction phenomenon Source: http://upload.wikimedia.org/wikipedia/commons/b/b9/Refraction-with-soda-straw.jpg http://media.digitalcameraworld.com/files/2012/10/Photography_effects_bending_light_refraction_NIK12.zone_4.refraction.jpg
37. 37. Apparent Depth (an effect of refraction)
38. 38. Key Ideas 1. Refraction is the bending of light as it travels through one medium to another of a different density. 2. The ray model of light can be used to show the refraction of light. 3. Object in water appear closer to the surface than they really are. This is due to the refraction of light.
39. 39. Dispersion of Light 1. When a beam of white light travels through a prism, it is split into different colours. 2. This is because the different colours of white light bend or are refracted towards the normal through different angles. This occurs when the beam of white light enters and leaves the prism. 3. A spectrum of seven colours is produced. This splitting of white light is called dispersion.
40. 40. Key Ideas 1. The dispersion of white light is the splitting up of white light into its component colours. 2. The different colours in white light are refracted through different angles by a glass prism. This results in the dispersion of white light.
41. 41. Colours White light is made up of seven different colours (Red, Orange, Yellow, Green, Blue, Indigo, Violet). We classify these colours as primary and secondary colours. Primary colours are basic colours that can not be obtained by mixing other colours together. Primary colours are: red, green, blue. Secondary colours are formed by mixing primary clours. Secondary colours are: cyan, yellow, magenta.
42. 42. Colours
43. 43. How do we see colour? light source  Light from most light sources looks white, but actually contains all the colours of the spectrum; also known as the rainbow.  If an object looks blue, it is absorbing every colour except blue, which is reflecting off it and entering your eyes.  If an object looks orange, it is absorbing every colour except orange, which, again, is reflecting off and entering your eyes.  If an object looks red... (You get the idea!)
44. 44. Key Ideas 1. Red, green, blue are primary colours of light which can be mixed to form the secondary colours of light : cyan, yellow and magenta. 2. The colour of an object depends on the type of coloured light that is reflected off its surface.
45. 45. Resources Joan Fong. Lower Secondary Science Matters Volume B Second Edition. Marshall Cavendish. http://www.childrensuniversity.manchester.ac.uk/interactives/science/brainandsenses/eye/ http://www.cyh.com/HealthTopics/HealthTopicDetailsKids.aspx?p=335&np=152&id=1730 Pictures Credits http://photos1.blogger.com/blogger/5361/1488/1600/forest1.0.jpg https://encrypted- tbn2.gstatic.com/images?q=tbn:ANd9GcT9SJp0ro8CgVLYTnb4bytGF7cxFoPptNy QeWRdZzblfN8lbYh1 http://hqwide.com/wallpapers/l/1366x768/22/landscapes_night_stars_galaxies_ guy_torch_flashlight_beam_1366x768_21690.jpg http://www.edplace.com/userfiles/image/man's%20shadow.jpg http://shop.sealomatic.net/images/1317269359817440511723.jpeg http://www.it.iitb.ac.in/ekshiksha/images_light_VIII/figure_9.JPG http://0.tqn.com/d/animatedtv/1/0/i/A/quimbybanner.jpg http://shirley.moodle2.net.nz/pluginfile.php/5670/mod_imscp/content/1/ess- sci-assets/programme-assets/images/z_block.jpg
46. 46. http://earth.rice.edu/Space_Update/updating/spaceweather/data/sun/eclipses/eclipse_diag ram.jpg http://www.ambitionarts.com/images/dancer_mirror.jpg http://cdn.instructables.com/FR4/B3NZ/GX5XJVBA/FR4B3NZGX5XJVBA.LARGE.jpg http://media2.apnonline.com.au/img/media/images/2013/04/25/WDN_25-04- 2013_ROP_03_Periscope%20rifle%2004_fct848x522x126_t460.jpg http://webs.mn.catholic.edu.au/physics/emery/assets/hsc_as3.gif http://images.wisegeek.com/dentist-inspecting-a-patient.jpg http://solarcellcentral.com/images/top_pic_csp_page.jpg http://www.energy.siemens.com/co/pool/hq/power-generation/power- plants/csp/solar_parabol_large.jpg http://static.fairfaxrural.com.au/multimedia/images/large/1996913.jpg http://olc.spsd.sk.ca/de/physics20/light/light_images/flashlight2a.jpg http://i1063.photobucket.com/albums/t507/cmusngi2929/My%20CLS55%20AMG%20Rebui ld/Headlights1RE.jpg http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/light-and- sight/sci-media/images/convex-mirror/685505-1-eng-NZ/Convex-mirror.jpg http://colorschemetools.net/cms.ashx?req=Image&imageid=7baf807d-ca1d-46dd-9eaf- 4dc50b711656&key=Additive%20color Video Credit http://www.youtube.com/watch?v=N1-zjbRqYXk https://www.youtube.com/watch?v=jtTBOMVMSYM