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# Light

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GCSE Physics double award notes

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### Light

1. 1. Waves- Light GCSE Physics
2. 2. Learning Intentions <ul><li>State how light travels </li></ul><ul><li>Recall how objects can be seen by the eye </li></ul><ul><li>State and use the law of reflection for simple problems </li></ul>
3. 5. Do you see what I mean? <ul><li>A ray of light can be represented as a simple straight line with an arrow pointing the direction the light is travelling. </li></ul>Luminous Non-Luminous Directly into our eye Reflected into our eye
4. 6. The Facts of Light <ul><li>Light is a form of energy </li></ul><ul><li>We see an object when the light energy leaving it enters our eye. </li></ul><ul><li>Objects which give out their own light are called luminous </li></ul><ul><li>Those that do not give out light scatter the light that falls on them are called non-luminous </li></ul><ul><li>Light travels in straight lines in the form of a transverse wave </li></ul>
5. 7. Light Reflecting <ul><li>Page 93 </li></ul><ul><li>Using the Method from page 93 find out how the angle of incidence is related to the angle of reflection </li></ul><ul><li>Watch the straight-forward demo and repeat for 3 different rays of light </li></ul>
6. 8. Normal Incident Ray Reflected Ray Angle of incidence Angle of reflection Smooth Plane Surface Angle of incidence = Angle of reflection Light Reflection
7. 9. Learning Intentions <ul><li>Investigate the path of a light ray through a glass block </li></ul><ul><li>Recall the term ‘ refraction ’ and predict how light is refracted in different media </li></ul>
8. 12. Refraction Experiment <ul><li>Investigate how light travels as it passes from air to glass, then from glass to air </li></ul>
9. 13. Results Table From Air to Glass Angle of Incidence Angle of Refraction 1. 2. 3. 4. From Glass to Air Angle of Incidence Angle of Refraction 1. 2. 3. 4.
10. 14. What to do…… <ul><li>Draw around the Perspex block on a piece of paper. </li></ul>
11. 15. The Normal <ul><li>Mark on a line known as the NORMAL perpendicular to the surface of the block. </li></ul>For the light ray entering the block and the light ray leaving the block mark each ray with two crosses. Draw in the incident ray , emergent ray , remove the block and then join up the two rays. Repeat two more times with the light ray entering the block at different angles.
12. 16. Results If the light ray entered the block parallel to the normal then it travels through un-deviated. If the incident ray enters the block at an angle to the normal then the direction of the ray changes as it enters and leaves the block, the light ray has been refracted. Does the angle of incidence …… … affect the angle of refraction?
13. 17. Air to Glass Angle of Incidence Angle of Refraction 1. 2. 3. Glass to Air Angle of Incidence Angle of Refraction 1. 2. 3.
14. 18. What happened…… <ul><li>As the light ray moved from air into perspex? </li></ul><ul><li>As the light ray moved from perspex into air? </li></ul><ul><li>If the angle of incidence = 0 °? </li></ul><ul><li>What do you notice about the incident ray and the emergent ray? </li></ul>
15. 19. Dense Material Less Dense Material Normal Incident Light Refracted Light Angle of Incidence Angle of Refraction
16. 20. Gobi Desert Mirage
17. 23. Air to Perspex angle of incidence > angle of refraction <ul><li>As the light ray moved from air into perspex it moved towards the normal. </li></ul><ul><li>If light rays move from a less dense material (air) to a more dense material (perspex) they ‘bend’ towards the normal. </li></ul> i >  r
18. 24. Perspex to Air angle of incidence < angle of refraction <ul><li>As the light ray moved from perspex into air it moved away from the normal. </li></ul><ul><li>If light rays move from a more dense material (perspex) to a less dense material (air) they ‘bend’ away from the normal. </li></ul> i <  r
19. 25. Angle of incidence = 0 ° <ul><li>When the angle of incidence is 0  the light ray is not deviated from its path. </li></ul><ul><li>Un-deviated light ray </li></ul>
20. 26. Refraction- summary table Angle of Incidence greater than / less than angle of refraction Angle of Incidence greater than / less than angle of refraction Angles Towards / Away from the normal line Towards / Away from the normal line Change of direction Increase / Decrease Increase / Decrease - From less dense to dense (air to water) - From dense to less dense (water to air) Change of speed Change of optical density
21. 27. Refraction <ul><li>Many surfaces also refract light: rather than bouncing off the surface, some of the incident ray travels through the surface, but at a new angle. </li></ul>
22. 28. Learning Intentions <ul><li>Recall the term ‘ refraction ’ and predict how light is refracted in different media </li></ul><ul><li>Draw light ray diagrams to illustrate ‘ apparent depth ’ </li></ul>
23. 29. A trick of the Light Image Water Air
24. 31. Apparent Depth <ul><li>When light travels from a dense to a less dense material it bends away from the normal (speeds up) </li></ul><ul><li>Our eye senses that light travels in a straight line </li></ul><ul><li>The object’s image ‘appears’ to be closer to the surface of the water. </li></ul>Image Water Air
25. 32. Learning Intentions <ul><li>Investigate the path of a light ray of white light as it passes through a glass prism </li></ul><ul><li>Recall the mean of the terms ‘ dispersion ’ and ‘ spectrum ’ </li></ul><ul><li>Relate the wavelength of light to refraction </li></ul>
26. 37. Dispersion Red light is refracted least. Violet light is refracted the most. R O Y G. B I V ed range ellow reen lue ndigo iolet White light
27. 41. Dispersion (page 95) The white light ray is split into a spectrum of colours. This is known as dispersion . The different colours of light have different wavelengths . Different wavelengths are refracted different amounts. White light Glass prism
28. 42. Dispersion Summary Red/violet Refracted more/less by glass Longer/shorter wavelength Red/violet Refracted more/less by glass Longer/shorter wavelength
29. 43. Learning Intentions <ul><li>recall that visible light is one of many types of electromagnetic waves </li></ul><ul><li>state all types of EM waves </li></ul><ul><li>state the similarities and differences between EM waves </li></ul>
30. 47. Light- Mirror Image GCSE Physics
31. 48. Learning Intentions <ul><li>Recall how an image is viewed in a mirror </li></ul><ul><li>State the differences between the object and its mirror image </li></ul><ul><li>Use ray diagrams to demonstrate how an image appears in a mirror </li></ul>
32. 49. Uses of Reflection <ul><li>The most common use of reflection is to view objects using a mirror (shiny flat surface). </li></ul><ul><li>In science we refer to the reflection as an ‘image’ in the mirror. </li></ul>
33. 51. The Image in a Plane Mirror <ul><li>The characteristics of images in a plane mirror are: </li></ul><ul><li>upright </li></ul><ul><li>virtual (behind the mirror and cannot be projected on a screen) </li></ul><ul><li>laterally inverted (right side of object is left side of image) </li></ul>R R Object Image Mirror
34. 52. Image size and distance For a plane mirror the size of the image is the same as the object’s and the image distance from the mirror is the same as the object’s distance from the mirror. See page 94 for extended notes on an image in a plane mirror mirror Object Image
35. 53. The image in a Plane mirror, pg 94
36. 54. Light- Shadows GCSE Physics
37. 55. Shadows <ul><li>Light can travel through materials which are transparent, e.g. air, glass or water. </li></ul><ul><li>If light cannot travel through a material it is called opaque , e.g. metal, wood etc. </li></ul><ul><ul><ul><li>- If an opaque object is placed in the way of a beam of light a shadow is created. </li></ul></ul></ul><ul><li>- The kind of shadow that is formed depends on the size of the light source. </li></ul>
38. 56. Ray diagrams and shadows
39. 57. Point Light Source A dark shadow with sharp edges is produced. The shadow is called the umbra
40. 58. The moon is in complete shadow of the Earth. Where on the diagram is the umbra? umbra Click Here
41. 60. Extended Light Source The shadow seen on the screen Partial Shadow- penumbra Umbra A hazy shadow with undefined edges is produced (penumbra) which fades into a complete shadow (umbra) Larger Hole
42. 61. Where on the diagram is the umbra? Where is the penumbra? penumbra umbra
43. 64. Application of all this… <ul><li>Why is lighting important in- </li></ul><ul><li>Stadium </li></ul><ul><li>Workshop </li></ul><ul><li>Office or school </li></ul><ul><li>Theatre </li></ul>