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Light

Light. Complete Physics pages for IGCSE 139 to 168. OPTICS Lens 3.2 (c) Thin converging lens Core • Describe the action of a thin converging lens on a beam of light • Use the term principal focus and focal length • Draw ray diagrams to illustrate the formation of a

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Light

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  1. Light Complete Physics pages for IGCSE 139 to 168

  2. OPTICS Lens 3.2 (c) Thin converging lens Core • Describe the action of a thin converging lens on a beam of light • Use the term principal focus and focal length • Draw ray diagrams to illustrate the formation of a real image by a single lens 3.2 (d) Dispersion of light Core • Give a qualitative account of the dispersion of light as shown by the action on light of a glass prism 3.2 (e) Electromagnetic spectrum Core • Describe the main features of the electromagnetic spectrum and state that all e.m. waves travel with the same high speed in vacuum • Describe the role of electromagnetic waves in: – radio and television communications (radio waves) – satellite television and telephones (microwaves) – electrical appliances, remote controllers for televisions and intruder alarms (infrared) – medicine and security (X-rays) • Demonstrate an awareness of safety issues regarding the use of microwaves and X-rays IGCSE SYLLABUS

  3. Reflection

  4. incident ray angle of incidence, i normal angle of reflection, r mirror reflected ray Law of Reflection The angle of incidence (i) is equal to the angle of reflection (r) Note: Both angles are measured with respect to the ‘normal’. Thisis a construction line that is perpendicularto the reflecting surface at the point ofincidence.

  5. image object construction lines (virtual light rays) normals plane mirror The image formed by a plane mirror • The image produced by the plane mirror is: • The same size as the object • The same distance behind the mirror as the object is in front • Upright (the same way up as the object) • Back-to-front compared with the object (lateral inversion) • Virtual

  6. Real and virtual images REAL images are formed where light rays cross after reflection by a mirror or refraction by a lens. Real images can be cast onto a screen. Example: A projector image VIRTUAL images are formed where light rays only appear to come from. A virtual image cannot be cast onto a screen. Example: The image formed by a plane mirror

  7. Choose appropriate words to fill in the gaps below: The law of reflection states that the angle of _________ is always _______ to the angle of incidence. Both angles are measured relative to the _________, a line that is at _______ degrees to the reflecting surface at the point of reflection. A plane mirror forms a _______ image which is unlike a _____ image in that it cannot be cast onto a screen. The image in a plane mirror is also the same ______ and the same way up as the object. reflection equal normal ninety virtual real size WORD SELECTION: normal virtual size reflection real equal ninety

  8. Optical illusions - by eChalk BBC KS3 Bitesize Revision: KS3 Light Contents Page What is light? Seeing Test bite on KS3 Light Law of Reflection - NTNU - features a movable plane mirror Reflection in a plane mirror - eChalk Balloon blasting game - eChalk Height of mirror and image seen - NTNU Virtual image formation - eChalk Image formed by a plane mirror - NTNU Reflection and images from two mirrors at 90 degrees to each other - NTNU Law of Reflection - Crocodile Clip Presentation BBC KS3 Bitesize Revision: Reflection & Scattering Simulations

  9. principal focus F C centre of curvature focal length, f radius of curvature, r Concave mirror A concave mirror is like the inside of a spoon. concave mirror principal axis O centre of the mirror

  10. Mirror definitions The principal axis is a construction line that is perpendicular to and passes through the centre of the mirror, O. The principal focus, F is the point through which all rays travelling parallel to the principal axis before reflection pass through or appear to come from after reflection. The focal length, f is the distance from the centre of the mirror, O to the principal focus, F. The centre of curvature, C is the centre of the circle of which the surface of the mirror is a part. The radius of curvature, ris the distance along the principal axis between the centre of the mirror, O and the centre of curvature and equal toTWICE the focal length, f of the mirror.

  11. concave mirror F Standard rays – concave mirror (a) Rays incident parallel to the principal axis pass through the principal focus after reflection. principal axis

  12. centre of curvature F principal axis C (b) Rays passing through the centre of curvature before reflection are reflected back along their initial path.

  13. O (c) Rays striking the centre of the mirror are reflected as if the mirror was flat.

  14. object C O F image Concave mirror images 1. Object more than the radius of curvature away from the mirror. Use: Satellite receiver (with microwaves) The image formed is: Smaller than the object (diminished) Between F and C Inverted (upside down) Real

  15. object O C F image 2. Object between F and C Use: Satellite transmitter (with microwaves) The image formed is: Larger than the object (magnified) Beyond C Inverted Real

  16. object image C F observer 3. Object nearer than the principal focus Use: Makeup and shaving mirrors The image formed is: Larger than the object On the other side of the mirror from the object Upright Virtual

  17. convex mirror F principal axis Standard rays – convex mirror (a) Rays incident parallel to the principal axis appear to come from the principal focus after reflection.

  18. convex mirror C principal axis F (b) Rays heading for the centre of curvature before reflection are reflected back along their initial paths.

  19. O (c) Rays striking the centre of the mirror are reflected as if the mirror was flat.

  20. object C F image observer Convex mirror images Objects at all distances from a convex mirror Use: Security mirrors The image formed is: Smaller than the object On the other side of the mirror from the object Upright Virtual Convex mirrors give a wide field of view

  21. Magnification magnification = image height object height Question: Calculate the magnification if a mirror produces an image of 40cm from an 8cm sized object. magnification = image height / object height = 40cm / 8cm magnification = 5 x

  22. Answers Complete: 8 x 15 cm 5 cm 3 x

  23. Choose appropriate words to fill in the gaps below: There are two types of curved mirror, __________ and convex. Concave mirrors look like the _____ of a spoon. Concave mirrors __________ light parallel to the principal axis so that all the rays pass through the __________ focus. Makeup mirrors can be concave in order to provide a __________ view of the face. Light is diverged by _________ mirrors. These always produce _________ images and are used to provide a wide field of view which is especially useful for ____ rear view mirrors. concave inside converge principal virtual convex magnified car WORD SELECTION: converge magnified concave principal car convex inside virtual

  24. Lens / mirror effect on a beam of light - NTNU Tiger image formation by a plane or curved mirror - NTNU Mirage of pig formed by a concave mirror - includes UTube clip - NTNU Curved mirror images / ray diagrams - NTNU Simulations

  25. Refraction

  26. Refraction occurs when a wave changes speed as it passes from one region to another. This speed change usually causes the wave to change direction. Water waves slow down as they pass over from a deeper to a shallower region. Light slows down as it passes from air into glass, perspex or water.

  27. AIR GLASS normal angle of refraction angle of incidence Refraction of light at a plane surface (a) Less to more optical dense transition (e.g. air to glass) Light bends TOWARDS the normal. The angle of refraction is LESS than the angle of incidence.

  28. angle of refraction normal angle of incidence WATER AIR (b) More to less optical dense transition (e.g. water to air) Light bends AWAY FROM the normal. The angle of refraction is GREATER than the angle of incidence.

  29. Refraction experiment Typical results: No deviation occurs when the angle of incidence is zero. Increasing the angle of incidence increases the deviation.

  30. normals observer AIR WATER image object at the bottom of a pool Why a pool appears shallow

  31. A B D E C F Complete the paths of the RED light rays:

  32. white light prism spectrum Dispersion A prism splits the colours of white light into the spectrum. This is called dispersion. Violet light deviates the most, redthe least.

  33. Choose appropriate words to fill in the gaps below: Refraction occurs when a wave changes ______ as it crosses the boundary between two regions. The _________ of the wave also usually changes. Light rays deviate ________ the normal when they pass from less dense air to more dense _________. The greater the angle of incidence the greater is the _________. Different ______ of light deviate by different amounts. Violet deviates the _____. A prism can be used to split the colours of white light into a spectrum. This is called _________. speed direction towards perspex deviation colours most dispersion WORD SELECTION: towards deviation most dispersion direction perspex speed colours

  34. Refraction - Powerpoint presentation by KT Light Refraction - Fendt Reflection & Refraction at a boundary - NTNU Refraction animation - NTNU - Does not show TIR effect Law of Refraction - Crocodile Clip Presentation Prism - non dispersive reflections and refractions - NTNU Prism/Lens - non dispersive refraction and reflections - NTNU BBC KS3 Bitesize Revision: Refraction Light moving from water to air - NTNU Where is the fish? - refraction by water - NTNU The appearance of an object under water / ray diagram - NTNU How a fish sees the world - NTNU Fibre optic reflection - NTNU BBC Bitesize Revision: Optical fibres Dispersion - Powerpoint presentation by KT Dispersion of light using a prism - NTNU - prism apex angle can be changed Prism showing light dispersion for different colours - Explore Science Dispersion - Crocodile Clip Presentation Sequential Puzzle on Colour Spectrum order- by KT  - Microsoft WORD Prism - multishape prism and single light ray - no extra reflections - netfirms BBC KS3 Bitesize Revision: Dispersion Simulations

  35. Lenses

  36. principal focus centre of the lens O F principal axis converging lens focal length, f Converging lens With glass and plastic lenses a converging lens has a convex shape. Converging lens with a parallel beam of light

  37. principal focus F principal axis O diverging lens focal length, f Diverging lens With glass and plastic lenses a diverging lens has a concave shape. Diverging lens with a parallel beam of light

  38. Lens definitions The principal axis is a construction line that is perpendicular to and passes through the centre of the lens. The principal focus, F is the point through which all rays travelling parallel to the principal axis before refraction pass through or appear to come from after refraction. The focal length, f is the distance from the centre of the lens, O to the principal focus, F.

  39. principal focus F principal axis Standard rays – converging lens (a) Rays incident parallel to the principal axis pass through the principal focus after refraction.

  40. centre of the lens O (b) Rays passing through the centre of the lens are not deviated.

  41. F F principal axis (c) Rays passing through the principal focus before refraction are refracted parallel to the principal axis.

  42. object O 2F F 2F image F Converging lens images 1. Object more than twice the focal length distant from a converging lens The image is real (the light rays really go there).The image is inverted (it is upside down).The image is smaller than the object. (Diminished)

  43. object O 2F F 2F image F Converging lens images 1. Object more than twice the focal length distant from a converging lens Uses: Camera and Eye The image formed is: Smaller than the object (diminished) Between the F and 2F Inverted (upside down) Real

  44. object 2F F 2F F image 2. Object between F and 2F • As above, you can see that the image is not the same as the object.The image is still real and inverted but it is now bigger than the object.

  45. object 2F F 2F F image 2. Object between F and 2F Use: Projector The image formed is: Larger than the object (magnified) Beyond 2F Inverted Real

  46. image F object F observer • The image is called virtual because the light rays never really go there(compare this with a real image).The image is called upright because it is the right way up 3. Object nearer than the principal focus

  47. image F object F observer 3. Object nearer than the principal focus Uses: Magnifying glass The image formed is: Larger than the object On the same side of the lens as the object Upright Virtual

  48. diverging lens F principal axis Standard rays – diverging lens (a) Rays incident parallel to the principal axis appear to come from the principal focus after refraction.

  49. O (b) Rays passing through the centre of the lens are not deviated.

  50. principal axis F O (c) Rays heading for the principal focus before refraction are deviated parallel to the principal axis.

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