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# Light and Sight

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• 10A got to here just intro TIR and CA
• ### Light and Sight

1. 1. WAVES● What are waves? What arent they? Give some examples.
2. 2. WAVES A wave consists of oscillations which move without carrying matter with them. The oscillations carry energy.A wave can be used to carry the energy itself, or it can be used to carry a signal.
3. 3. PulseA pulse is a single wave bump or a “disturbance”.A pulse can easily be sent down a string or spring. A wave is made of lots of regular pulses.
5. 5. Amplitude Amplitude determines how much energy the waves have. More amplitude = brighter light, louder sound etc. Wavelength = λ = lowercase (Greek) lambda. What is the relationship between v, f and λ?http://upload.wikimedia.org/wikipedia/commons/f/fa/Wave.JPG
7. 7. Longitudinal WavesLongitudinal waves are the opposite of transverse waves.The direction of propagation is the same as the direction of vibration in the medium. https://encrypted-tbn1.google.com/ima
8. 8. Example William is swimming at a beach with wavesconstantly coming from the sea. He estimates that the distance between the wave crests is 6m, andtwo wave crests pass him every second. How fast are the waves travelling?
9. 9. Example 2David shouts across the room at Aska. He shouts with a low frequency of 5000 Hertz, and the waves travel at a speed of 340 m/s. What is the wavelength of Davids voice?
10. 10. Quick Review● Write a definition in your own words of: A. Frequency B. Wavelength C. Wave speed D. Amplitude E. Crest F. Trough● State and explain the wave equation, including explaining why it works.
11. 11. A. What is the time period of a wave if two wavespass every twenty seconds?B. What is the frequency of the wave from A?C. Hard: what is the relationship between time periodand frequency (for any wave)? Write it like a mathequation, using f for frequency and T for time period.It is ok if you cant do this question :)
12. 12. The speed of sound in air is about three hundred and forty metres persecond.10. What is the frequency of a sound wave with a wavelength of 6.8meters?11. Humans can hear approximately twenty hertz to twenty kilohertz.Calculate the minimum and maximum wavelengths humans can hear.12. The speed of light is 300 000 000 (3 * 108) meters per second.Calculate the wavelength of red light, given that it has a frequency of 500000 000 000 000 (5 * 1014) Hertz.
13. 13. The Microwave● Calculate the wavelength of the microwaves in a microwave oven.
14. 14. Maxence is swimming in a wave pool. The wave generator creates two waves each second, andthey travel at a speed of three metres per second. A. Will Maxence notice the wave crests or troughs? B. How far apart are two crests or two troughs?
15. 15. Quantity Symbol Formula UnitSpeed/ V metres pervelocity s = f*λ second (m/s) f = v/λ Hertz (Hz) λ (lambda)
16. 16. Sound● Sound is a longitudinal wave.● It can travel through liquids and all gases.● An oscilloscope can convert sound waves to visible transverse waves.● Humans can hear from around 20 Hz to 20 kHz, and the range decreases with age. A phone can typically carry waves ranging from 300Hz to 3.4kHz.
17. 17. Pitch and Loudness● Recall humans can hear from 20 Hz to 20 kHz.● Frequency = pitch● Amplitude = volumehttp://www.sciencelearn.org.nz/Contexts/The-Noisy-Reef/Sci-Media/Images/Graphs-of-sound-waves
18. 18. Frequency Ranges● Drum = 20Hz● Low note from a singer = 100Hz.● High note from singer = 1000Hz.● Whistle = 10 000 Hz. All images from wikimedia commons.
19. 19. Testing your Speakers● Use onlinetonegenerator.com to test the speaker in your computer OR smartphone (or other device).● Either wear headphones (not too loud!) or work in groups, for obvious reasons!
20. 20. Testing Skype● Use a tone generator software (tonegen is free but expires, or use a smartphone) to test the frequency response range of skype (or your microphone).
21. 21. Noise and decibels (dB)● Noise is unwanted sound.● Sound level is measured in decibels (dB).http://impact.books.officelive.com/ProtectYourHearing.asp
22. 22. Sound and Waves Review1. What is a wave?2. Describe the two main types of waves.3. State the wave equation, and the formulawhich relates them.4. Name one property of a wave which is not partof the wave equation. How do we observe thisproperty of sound waves.5. How do we observe frequency of soundwaves?6. State the maximum audible range of humans.
23. 23. Ripple Tank Here● Either the real one or a virtual one :) http://phet.colorado.edu/en/simulation/wave-interfer
24. 24. Go to phet.colorado.edu/web-pages/simulations-base.html● Go to Sound and Waves. Choose “Water” (top left), “one drip” and “no barrier” (centre right).● Devise an experiment to calculate the speed of the waves in the water.● Aim: To measure the effect of frequency and amplitude on wave speed in water.● Prediction: As the frequency increases, the wave speed will ____________ because ___________________________________________. As the amplitude increases, the wave speed will ____________ because ___________________________________________
25. 25. Speed, Frequency, Wavelength The velocity of waves in a medium is not affected by amplitude or frequency.● What happens to the wavelength as the frequency increases?● What happens to the frequency as the wavelength increases?● Hard: What is the mathematical relationship between frequency and wavelength?
26. 26. Wavefronts ● A wave can be drawn as a series of lines, where each line represents a crest. ● We can also draw them as a line through the middle of the wave, often called a ray. ● What is the mathematical relationship between the ray and the wavefronts?http://www.studyphysics.ca/newnotes/20/unit03_mechanicalwaves/chp141516_waves/lesson43.h
27. 27. Reflection of Waves● The region two different media meet is called a boundary.● At a boundary a wave can reflect. http://science.jburroughs.org/mschober/waveslite/prob
28. 28. Refraction of Waves● If a wave enters a different medium, its speed will probably change.● A change in speed causes a change in direction.● Depth of water changes the speed of waves. Image from Giancoli Physics, Sixth Edition removed.
29. 29. Diffraction● As waves pass a barrier or through a gap in a barrier, they spread out.● The diffraction is generally only noticeable if the gap is not much larger than one wavelength. http://innovativescience.blogspot.com/2011/02/di
30. 30. Textbook work● All questions on page 95.
32. 32. Electromagnetic Spectrum Wave Approximate Approximate Uses Frequency Wavelength Radio waves 103m Microwaves 10-2m Infra Red 10-5m Waves Visible Light 5 *10-7m Ultraviolet Light 10-8m X Rays 10-10m Gamma Rays 10-12mseeing things; for cell phones and for heating things which contain water; transmittingsignals; photographing bones which cant be seen with visible light; remote controls;identifying genuine or forged documents, and for purification of air and water; to sterilisefood and seeds, and for cancer treatment
33. 33. The words seeing things; for cell phones and for heatingthings which contain water; transmitting signals; photographing bones which cant be seen withvisible light; remote controls; identifying genuine or forged documents, and for purification of air and water; to sterilise food and seeds, and for cancer treatment
34. 34. Signals● Electromagnetic waves are used to carry signals.● A continuous variation is called an analog signal, whereas digital signals are represented as numbers. Most early communications devices used analogue, while most modern devices use digital (exceptions?). http://news.bbc.co.uk/2/hi/technology/6142998.stm
35. 35. Signals● Electromagnetic waves are used to carry signals.● A continuous variation is called an analog signal, whereas digital signals are represented as numbers. Most early communications devices used analogue, while most modern devices use digital (exceptions?). http://news.bbc.co.uk/2/hi/technology/61429
36. 36. Radio Waves● Radio waves are used to carry signals for radio, TV and mobile phones.● Either the frequency or amplitude must be changed (modulation) to carry the signal. http://www.softwareforeducation.com/
37. 37. Frequency Bands● Different frequencies (“bandwidths”) are used for different applications. They must be managed(as a resource) to ensure that people dont use the same frequency in the same place. http://en.wikipedia.org/wiki/Radio_spectrum
38. 38. AM and FM● AM radio waves can diffract around hills and mountains, so are best for rural areas.● FM signals are better quality, and are generally used in urban areas. http://scienceaid.co.uk/physics/wa
39. 39. Fibre Optics ● Fibre optics are thin glass cables which carry electromagnetic radiation(IR or visible light) inside them. ● They are thinner and lighter than electrical wire, and lose less signal over long distances.http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Fibreoptic.jpg/220px-Fibreoptic.jpg
40. 40. Radio Waves● Radio waves are used to carry signals for radio, TV and mobile phones.● Either the frequency or amplitude must be changed (modulation) to carry the signal. http://www.softwareforeducation.com/wikileki/index.php?title=FM
41. 41. Diffraction of AM and FM● AM radio waves can diffract around hills and mountains, so are best for rural areas.● FM signals are better quality, and are generally used in urban areas. http://scienceaid.co.uk/physics/waves/radio.html
42. 42. Frequency Bands● Different frequencies (“bandwidths”) are used for different applications. They must be managed(as a resource) to ensure that people dont use the same frequency in the same place. http://en.wikipedia.org/wiki/Radio_spectrum
43. 43. Absorption by the Atmospherehttp://en.wikipedia.org/wiki/File:Atmospheric_electromagnetic_opacity.svg
44. 44. The Dog at the Beach http://www.flickr.com/photos/velo4it/1746214612/
45. 45. How the Dog Runs Sand Sea http://commons.wikimedia.org/wiki/File:2009-11-19_(31)_Branch,_Ast.JPG http://commons.wikimedia.org/wiki/File:Brittany_Spaniel_Dog.jpghttp://commons.wikimedia.org/wiki/File:Dog_retrieving_stick.jpg
46. 46. How the Dog Runs Sand Sea Sand http://commons.wikimedia.org/wiki/File:2009-11-19_(31)_Branch,_Ast.JPGhttp://commons.wikimedia.org/wiki/File:Dog_retrieving_stick.jpg http://commons.wikimedia.org/wiki/File:Brittany_Spaniel_Dog.jpg
47. 47. LightLight is an electromagnetic wave, therefore:1) It travels at a speed of _________.2) It can travel through _________. 3) As a wave, it can d______, r_______ or r________.●Light can be drawn as rays, where the ray is perpendicularto the w___________.●Light (rays) must travel in s______ l_______.●The eye detects light (more later). Some things emit light(eg __________) while most things we see reflect light (eg_____________________) http://commons.wikimedia.org/wiki/File:Gluehbirne_2_db.jpg
48. 48. Reflection of Light ● Most objects reflect light but scatter it in all directions. Mirrors (and other shiny surfaces) reflect light so that they produce images. ● Reflected rays follow two rules: ι ρ θ =θ 1. The angle of incidence equals the angle of reflection. 2. The incident ray, normal and the reflected ray all lie in the same plane. Angle of incidence Angle of reflectionhttp://upload.wikimedia.org/wikipedia/commons/b/b2/Ray_optics_diagram_incidence_reflection_and_refraction.svg
49. 49. Images from Plane Mirrors ● Plane mirrors form images which are: 1. the same size 2. the same distance from the mirror 3. laterally inverted (left and right swapped). ● A great site below:http://www.kss.sd23.bc.ca/staff/jstracha/physics_11/course_material/unit8/U08L01/pages/ray7_plane_jpg.htm
50. 50. Bookwork● Page 85 and 87.
51. 51. Refraction● When light enters a different medium, it changes direction, unless it enters along the normal (an angle of incidence of ______).● As light enters a more dense medium, it slows down, and bends ____________ the normal.● As light enters a less dense medium, it speeds up, and bends ____________ from the normal. http://www.daviddarling.info/images/refraction.gif
52. 52. The Brain● Recall that the part of the brain which subconsciously controls the eye thinks that light always travels in straight lines. http://www.mikecurtis.org.uk/light3.gif
53. 53. Why Something Looks Bent in Waterhttp://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Pencil_in_a_bowl_of_water.svg/1000p-Pencil_in_a_bowl_of_water.svg.png
54. 54. Refraction and Colour ● High frequency light (eg violet) is bent more than low frequency light (eg red). ● This is why a prism can separate white light into its different colours. ● This process is known as dispersion.http://upload.wikimedia.org/wikipedia/commons/0/06/Prism_rainbow_schema.png
55. 55. Angles
56. 56. The Semi-Circular BlockWhen light is shone towards the centre ofthe (semi) circle, the angle if incidence isalways ________.
57. 57. The Critical Angle is the angle for which therefracted ray has an angle of refraction of 90°.
58. 58. Total Internal Reflection● When light travels from a MORE dense medium to a LESS dense medium, it bends _____ _______ the normal.● If the refracted light has an angle of refraction greater than the critical angle, the light is instead reflected. This is called total internal reflection.
59. 59. Determining The Critical Angle ● Determine the critical angle for perspex. ● While you are using the ray boxes, also observe and draw how light refracts through a rectangular perspex block, and the convex and concave lenses.http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/light/images/criticalangle.pn