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# Light

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### Light

1. 1. PHYSICAL SCIENCE GRADE 11 TOPIC
2. 2. LIGHT: Geometrical Optics 1. Reflection of light 2. Refraction of light 3. Lenses
3. 3. Nature of light  Light is a form of energy  Light is a form of a word motion  The way in which light radiates from its source is similar to the way in which it ripples spread outwards across a pond.
4. 4. ● Everyday life situations that involve refraction of light. ● How the direction of light as it passes from one medium to another is associated with a change in velocity and wavelength. ● Provide visual examples to help you understand how refraction of light occurs.
5. 5. REFRACTION OF LIGHT
6. 6. 3rd period
7. 7. Refraction of Light • Refraction is the bending of a wave as it passes at an angle from one medium into another. • this occurs when the light’s velocity changes.
8. 8. Examples • Glass, water, ice, diamonds, and quartz are all examples of transparent media through which light passes through. * Keep in mind that the speed of light in these material is different.
9. 9. Direction of Light • Light travels in straight lines until it encounters another material where it is partially reflected and partially transmitted. • The angle of the ray when transmitted through the material changes and depends on the speed of light in the two materials.
10. 10. cont… • As light travels through a given medium, it travels in a straight line. However, when light passes from one medium into a second medium, the light path bends. • Refraction occurs only at the boundary; once the light has crossed the boundary between the two medias, it continues to travel in a straight line. Now the direction of that line is different than it was in the former medium.
11. 11. For Example:
12. 12. Example (cont.):
13. 13. Think about it Refraction of light happens everywhere. Take a moment and ask yourself: “Why do fish look larger in the water?” “What causes a spoon to appear bent in a glass of water?” “Why does light travel indefinitely in an optical cable?” And the most common question, “How are rainbows, and mirages formed?”
14. 14. Lenses
15. 15. Refraction  Waves bend towards the normal when entering a more dense medium. Incident ray Refracted ray
16. 16. Converging Lenses
17. 17. Diverging Lenses
18. 18. Ray Diagrams - Optical Centre Principle axis . F
19. 19. Optical Centre Principle axis Light rays passing along the principle axis are not refracted as they strike both surfaces at 90° Any ray passing through the Optical Centre can be thought of as passing straight through. In a thin lens the displacement is negligible.
20. 20. REFLECTION OF LIGHT We can see  luminous objects: as they give off light which enters our eyes. Non-luminous objects: as they reflect light from a source to our eyes.
21. 21. NATURE OF LIGHT Light is a form of energy. Light is a form of wave motion. The way in which light radiates from its source is similar to the way in which ripples spread outwards across a pond.
22. 22. NATURE OF LIGHT Light travels at a speed of 3 x 108 m/s through empty space. Light can be detected by human eye. This speed is equivalent to travelling 7 times round the Earth in less than a second! Light travels in straight lines.
23. 23. Light travels in straight lines.
24. 24. Light travels in straight lines.
25. 25. LIGHT RAYS The path along which light energy travels is called a ray. A light ray A bundle of light rays is a beam of light. Line represents the path along which light travels. Arrow represents the direction in which light travels.
26. 26. LIGHT BEAMS 3 different types of light beams : Parallel Beam : Light rays travels from very far away Divergent Beam : Light rays from a point source (not far away) Convergent Beam : Light rays meet at a point
27. 27. A reflecting surface Any shiny (smooth) surface. E.g a plane mirror Symbol of a plane mirror reflecting surface
28. 28. TERMS USED IN THE STUDY OF REFLECTION The incident ray The ray that approaches the mirror. incident ray
29. 29. The reflected ray The ray that bounces off the mirror. reflected rayincident ray
30. 30. TERMS USED IN THE STUDY OF REFLECTION The point of incidence The point where the incident ray meets the mirror. reflected rayincident ray point of incidence
31. 31. The normal The line that is perpendicular (at 90o) to the mirror. normal reflected rayincident ray
32. 32. The angle of incidence is represented by: i The angle between the incident ray and the normal. normal reflected rayincident ray i
33. 33. The angle of reflection is represented by r The angle between the reflected ray and the normal. normal reflected rayincident ray i r
34. 34. The angle of incidence is equal to the angle of reflection. i = r normal reflected rayincident ray i r
35. 35. The incident ray, the reflected ray and the normal at the point of incidence all lie on the same plane. We always see all of them on the flat piece of surface.
36. 36. The image is virtual. The image is upright. The image formed has the same size as the object. Image cannot be formed on the screen. Light rays do not meet at the image position. It is an imaginary image.
37. 37. IMAGE IN A PLANE MIRROR The image is as far behind the mirror as the object is in front of the mirror. Object distance d1 = Image distance d2 d1d2
38. 38. IMAGE IN A PLANE MIRROR The image is laterally inverted (left-to- right inversion) Left side of the object becomes the right side of the image.
39. 39. The following slides shows how you can apply laws of reflection
40. 40. To locate image formed in a plane mirror. EYE O
41. 41. Step 1 : Locate the image position. EYE I O
42. 42. Step 2 : Draw reflected rays (connect Image I to eye) EYE I O
43. 43. Step 3 : Draw incident rays. (connect object O to reflected rays) EYE I O
44. 44. USES OF REFLECTION Periscope Mirror in meter Optical testing Other uses
45. 45. This is commonly called short sighted. Distant object brought ‘closer’ Distant objects the lens is not stretched enough. (Too fat) Rays are focused in front of retina. Object close up are focused clearly. A diverging lens would cause distant rays to focus on the retina and normal sight is restored. Short Sighted
46. 46. Compound Microscope F• 2 F F F 2 F View this slide as slide show!
47. 47. REFERENCES • The Broken Pencil. (n.d.). The Broken Pencil. Retrieved March 06, 2014, from http://www.physicsclassroom.com/mmedia/optics/bp.cfm • Changing the Speed of Light. (n.d.). Optics For Kids. Retrieved March 06, 2014, from http://www.optics4kids.org/home/teachersparents/articles/the- refraction-of-light/ • The Direction of Bending. (n.d.). The Direction of Bending. Retrieved March 06, 2014, from http://www.physicsclassroom.com/class/refrn/U14L1e.cfm • Refractrion of Light. (n.d.). http://www.physicsclassroom.com. Retrieved March 06, 2014, from http://www.ece.gatech.edu/academics/outreach/step- up/lesson_plans/2010/Refraction/REFRACTION-OF-LIGHT.pdf
48. 48. • refraction of light. (n.d.). refraction of light. Retrieved March 06, 2014, from https://www.google.com/search?q=refraction+of+light&source=lnms&tbm =isch&sa=X&ei=TnluUpm9FNHpkAfSroC4AQ&sqi=2&ved=0CAcQ_AUoA Q&biw=1366&bih=664#imgdii=_ • Refraction and Sight. (n.d.). Refraction and Sight. Retrieved March 06, 2014, from http://www.physicsclassroom.com/class/refrn/u14l1b.cfm • http://www.slideshare.net/AlexanderZhongPing/physics-light- 21211682?qid=a46f0666-227d-45cb-a5f9- 70add51ddede&v=qf1&b=&from_search=6
49. 49. H T T P : / / W W W . S L I D E S H A R E . N E T / M I N E N H L E Z / M S - Z U N G U - 2 0 1 2 2 1 2 0 0 - 3 1 9 8 3 9 8 5 Link to my presentation