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Waves Presentation


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This is up until Wednesday 14th September

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Waves Presentation

  1. 1. WAVES <ul><li>What are waves? What aren't they? Give some examples. </li></ul>
  2. 2. WAVES A wave carries consists of oscillations which move without carrying matter with them. The oscillations carry energy. The energy can be used to carry a signal.
  3. 3. Pulse A pulse is a single wave 'bump' or a “disturbance”. A pulse can easily be sent down a string or spring.
  4. 4. Amplitude Amplitude determines how much energy the waves have. More amplitude = brighter light, louder sound etc.
  5. 5. Wavelength = λ = lowercase (Greek) 'lambda'. What is the relationship between v, f and λ? Waves
  6. 6. Transverse Waves
  7. 7. Longitudinal Waves Longitudinal waves are the opposite of transverse waves. The direction of propagation is the same as the direction of vibration in the medium.
  8. 8. Train Analogy Speed = frequency * wavelength. V=fλ λ λ λ λ λ λ
  9. 9. Example Stella is swimming at a beach with waves constantly coming from the sea. She estimates that the distance between the wave crests is 6m, and two wave crests pass her every second. How fast are the waves travelling?
  10. 10. Example 2 Avinarsh shouts across the room at Paul. 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 Avinarsh's voice?
  11. 11. Quick Review <ul><li>Write a definition in your own words of: A. Frequency B. Wavelength C. Wave speed D. Amplitude E. Crest F. Trough
  12. 12. State and explain the wave equation, including explaining why it works. </li></ul>
  13. 13. A. What is the time period of a wave if two waves pass every twenty seconds? B. What is the frequency of the wave from A? C. Hard: what is the relationship between time period and frequency (for any wave)? Write it like a math equation, using f for frequency and T for time period. It is ok if you can't do this question :)
  14. 14. The speed of sound in air is about three hundred and forty metres per second. 10. What is the frequency of a sound wave with a wavelength of 6.8 meters? 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 * 10 8 ) meters per second. Calculate the wavelength of red light, given that it has a frequency of 500 000 000 000 000 (5 * 10 14 ) Hertz.
  15. 15. The Microwave <ul><li>Calculate the wavelength of the microwaves in a microwave oven. </li></ul>
  16. 16. Hana is swimming in a wave pool. The wave generator creates two waves each second, and they travel at a speed of three metres per second. A. Will Hana notice the wave crests or troughs? B. How far apart are two crests or two troughs? Note for blog: This was not covered in class, but would be a good revision exercise.
  17. 17. Quantity Symbol Formula Unit Speed/ velocity V s = f* λ metres per second (m/s) f = v/ λ Hertz (Hz) λ (lambda)
  18. 18. Virtual Experiment <ul>Go to <li>Go to Sound and Waves. Choose “Water” (top left), “one drip” and “no barrier” (centre right).
  19. 19. Devise an experiment to calculate the speed of the waves in the water. </li></ul>
  20. 20. Wavefronts <ul><li>A wave can be drawn as a series of lines, where each line represents a crest.
  21. 21. We can also draw them as a line through the middle of the wave, often called a ray .
  22. 22. What is the mathematical relationship between the ray and the wavefronts? </li></ul>
  23. 23. Reflection of Waves <ul><li>The region two different media meet is called a boundary.
  24. 24. At a boundary a wave can reflect. </li></ul>
  25. 25. Refraction of Waves <ul><li>If a wave enters a different medium, its speed will probably change.
  26. 26. A change in speed causes a change in direction.
  27. 27. Depth of water changes the speed of waves. </li></ul>Image from Giancoli Physics, Sixth Edition. Please ask me if you would like to see the book it came from.
  28. 28.
  29. 29. Diffraction <ul><li>As waves pass a barrier or through a gap in a barrier, they spread out.
  30. 30. The diffraction is generally only noticeable if the gap is not much larger than one wavelength. </li></ul>
  31. 31. Electromagnetic Radiation <ul><li>Electromagnetic radiation is a family of waves which are made of an electric field and a magnetic field interacting with each other.
  32. 32. All EM Waves A. Are transverse B. Can travel through a vacuum C. Travel at c, 3*10 8 m/s </li></ul>
  33. 33. Speed, Frequency, Wavelength <ul>The velocity is always the same. <li>What happens to the wavelength as the frequency increases?
  34. 34. What happens to the frequency as the wavelength increases?
  35. 35. What is the mathematical relationship between frequency and wavelength? </li></ul>
  36. 36. The Electromagnetic Spectrum
  37. 37. Electromagnetic Spectrum Wave Approximate Frequency Approximate Wavelength Uses Radio waves 10 3 m Microwaves 10 -2 m Infra Red Waves 10 -5 m Visible Light 5 *10 -7 m Ultraviolet Light 10 -8 m X Rays 10 -10 m Gamma Rays 10 -12 m seeing things; for cell phones and for heating things which contain water; transmitting signals; photographing bones which can't be seen with visible light; remote controls; identifying genuine or forged documents, and for purification of air and water; to sterilise food and seeds, and for cancer treatment
  38. 38. The words seeing things; for cell phones and for heating things which contain water; transmitting signals; photographing bones which can't be seen with visible light; remote controls; identifying genuine or forged documents, and for purification of air and water; to sterilise food and seeds, and for cancer treatment
  39. 39. Signals <ul><li>Electromagnetic waves are used to carry signals.
  40. 40. A continuous variation is called an analogue signal, whereas digital signals are represented as numbers. Most early communications devices used analogue, while most modern devices use digital (exceptions?). </li></ul>
  41. 41. Radio Waves <ul><li>Radio waves are used to carry signals for radio, TV and mobile phones.
  42. 42. Either the frequency or amplitude must be changed (modulation) to carry the signal. </li></ul>
  43. 43. Frequency Bands <ul><li>Different frequencies (“bandwidths”) are used for different applications. They must be managed(as a resource) to ensure that people don't use the same frequency in the same place. </li></ul>
  44. 44. Absorption by the Atmosphere
  45. 45. The Ionosphere <ul><li>The ionosphere is a layer of charged particles in the upper atmosphere. Medium waves are reflected off the ionosphere, and this can be used to spread them around the Earth.
  46. 46. Microwaves pass through the atmosphere, and can be reflected off satellites to pass signals around the Earth. </li></ul>
  47. 47. AM and FM <ul><li>AM radio waves can diffract around hills and mountains, so are best for rural areas.
  48. 48. FM signals are better quality, and are generally used in urban areas. </li></ul>
  49. 49. Textbooks <ul><li>Physics for Higher Tier
  50. 50. Questions on page 95, 97 and 99. </li></ul>
  51. 51. Fibre Optics <ul><li>Fibre optics are thin glass cables which carry electromagnetic radiation(IR or visible light) inside them.
  52. 52. They are thinner and lighter than electrical wire, and lose less signal over long distances. </li></ul>
  53. 53. This lesson: SOUND <ul><li>Sound waves
  54. 54. Speed of sound
  55. 55. Noise and vibration
  56. 56. Pitch and volume (=frequency and amplitude)
  57. 57. Pages 100-107
  58. 58. 10A did the bookwork but not experiment Tuesday (fire drill)
  59. 59. 10B Wednesday
  60. 60. 10C Thursday (One slide completed already) </li></ul>
  61. 61. Sound <ul><li>Sound is a longitudinal wave.
  62. 62. It can travel through liquids and all gases.
  63. 63. An oscilloscope can convert sound waves to visible transverse waves.
  64. 64. Humans can hear from around 20 Hz to 20 kHz, and the range decreases with range. A phone can typically carry waves ranging from 300Hz to 3.4kHz. </li></ul>
  65. 65. Textbooks <ul><li>Physics for Higher Tier
  66. 66. Questions on page 95, 97 and 99, 101.
  67. 67. Write answers in the most efficient way for your learning. I will only check completion; they are not 'assignments' and all material is covered in the notes, </li></ul>
  68. 68. Pitch and Loudness <ul><li>Recall humans can hear from 20 Hz to 20 kHz.
  69. 69. Frequency = pitch
  70. 70. Amplitude = volume </li></ul> Pitch and volume image
  71. 71. Frequency Ranges <ul><li>Drum = 20Hz
  72. 72. Low note from a singer = 100Hz.
  73. 73. High note from singer = 1000Hz.
  74. 74. Whistle = 10 000 Hz. </li></ul>All images from wikimedia commons.
  75. 75. Testing Skype <ul><li>Use a tone generator software (tonegen is free but 'expires' to test the frequency response range of skype (or your microphone). </li></ul>
  76. 76. Noise and decibels (dB) <ul><li>Noise is unwanted sound.
  77. 77. Sound level is measured in decibels (dB). </li></ul> Decibels scale image
  78. 78. Antinoise <ul><li>An antinoise plays the a 'opposite' wave to sound in the air to cancel it out.
  79. 79. It is difficult because sound comes from all around and bounces off walls etc. </li></ul> Antinoise image
  80. 80. The Speed of Sound <ul><li>Sound is a longitudinal wave.
  81. 81. Try out the following simulations:
  82. 82.
  83. 83.
  84. 84. Sound can travel in many different media. Which properties of the medium will determine the speed of sound in it?
  85. 85. Answer: density (also elasticity – not grade 10 level).
  86. 86. Does sound travel faster in helium or air (mostly nitrogen)? Note: not covered with 10A yet </li></ul>
  87. 87. Measuring the Speed of Sound <ul><li>Load logger pro and open '33 – Speed of Sound'.
  88. 88. Formative – teacher view.
  89. 89. Instructions in handout.
  90. 90. Follow-up activities: Old IGCSE exam questions (handed out in class). </li></ul>
  91. 91. IGCSE June 2008 Question 2
  92. 93. Bookwork <ul><li>Read 102-107
  93. 94. Answer questions on page 103 and 107.
  94. 95. Note: this was only used for 10A on Tuesday 9/13 (fire drill); you will do the experiment and other slides next class. </li></ul>
  95. 96. Next time: <ul><li>The Sound of Music </li></ul>
  96. 97. Musical Notes <ul><li>A simple, 'pure' note is a sound wave of a single frequency, such as that produced by a tuning fork.
  97. 98. However, most things which produce sound (especially musical instruments) produce other notes, called overtones, which make notes of the same frequency sound different.
  98. 99. If two notes are an octave apart, one has double the frequency of the other. </li></ul>
  99. 100. Laboratory <ul><li>No need for 'approx'. Just round sensibly.
  100. 101. Compare your result to the official value. Write a comparison – more? Less? Reasonable? Why might they be different?
  101. 102. A number without a unit is meaningless. </li></ul>
  102. 103. Assessment <ul><li>Waves investigation and Presentation (summative - start presenting in two weeks).
  103. 104. Ripple Tank will be summative.
  104. 105. Speed of Sound and IGCSE exam will be formative.
  105. 106. We have now finished the sections on sound, waves and the EM spectrum. </li></ul>
  106. 110. Light Light is an electromagnetic wave, therefore: <ul><li>It travels at a speed of _________.
  107. 111. It can travel through _________. </li></ul><ul><li>As a wave, it can d______, r_______ or r________.
  108. 112. Light can be drawn as rays, where the ray is perpendicular to the w___________.
  109. 113. Light (rays) must travel in s______ l_______.
  110. 114. The eye detects light (more later). Some things emit light (eg __________) while most things we see reflect light (eg _____________________) </li></ul>
  111. 115. Electromagnetic Spectrum Visible light has a wavelength of approximately 400 to 750nm (_________________) . Our eyes are probably sensitive to these frequencies because ____________________ _____________________.
  112. 116. Lasers <ul><li>Laser stands for Light Amplification through Stimulated Emission of Radiation (not IGCSE).
  113. 117. Laser light is all the same frequency (c________) and all in phase, meaning that the troughs and crests are all in the same place. Lasers have many uses:
  114. 118. Fibre optics (data)
  115. 119. Medical Operations
  116. 120. Cds/DVDs </li></ul>
  117. 121.
  118. 122. Holograms A hologram is a 3D image made using lasers. They are often added to important documents and to make forgery more difficult.
  119. 123. Reflection of Light <ul><li>Most objects reflect light but scatter it in all directions. Mirrors (and other shiny surfaces) reflect light so that they produce images.
  120. 124. Reflected rays follow three rules: 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. </li></ul>Angle of incidence Angle of reflection θ i = θ r
  121. 125. Images from Plane Mirrors <ul><li>Plane mirrors form images which are:
  122. 126. 1. the same size 2. the same distance from the mirror 3. laterally inverted (left and right swapped).
  123. 127. A great site below: </li></ul>
  124. 128. Bookwork <ul><li>Page 85 and 87. </li></ul>
  125. 129. The Dog at the Beach (no need to load this URL unless you like pictures of dogs and/or the beach)
  126. 130. How the Dog Runs,_Ast.JPG
  127. 131. How the Dog Runs,_Ast.JPG
  128. 132. Refraction <ul><li>When light enters a different medium, it changes direction, unless it enters along the normal (an angle of incidence of ______).
  129. 133. As light enters a more dense medium, it slows down, and bends ____________ the normal.
  130. 134. As light enters a less dense medium, it speeds up, and bends ____________ from the normal. </li></ul>
  131. 135. The Brain <ul><li>Recall that the part of the brain which subconsciously controls the eye 'thinks' that light always travels in straight lines. </li></ul>
  132. 136. Why Something Looks Bent in Water
  133. 137. Refraction and Colour <ul><li>High frequency light (eg violet) is bent more than low frequency light (eg red).
  134. 138. This is why a prism can separate white light into its different colours.
  135. 139. This process is known as dispersion. </li></ul>
  136. 140. Angles
  137. 141. The Semi-Circular Block The angle if incidence is always ________.
  138. 142. The Critical Angle is the angle for which the refracted ray has an angle of reflection of 90 °.
  139. 143. Total Internal Reflection <ul><li>When light travels from aMORE dense medium to a LESS dense medium, it bends _____ _______ the normal.
  140. 144. 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. </li></ul>
  141. 145. Quick Experiment <ul><li>Determine the critical angle for perspex.
  142. 146. While you are using the ray boxes, also observe and draw how light refracts through a rectangular perspex block. </li></ul>
  143. 147. Fibre Optics
  144. 148. Why Do Diamonds Sparkle
  145. 149. Questions <ul><li>Page 89 & 91. </li></ul>
  146. 150. Convex Lenses A convex lens can produce a real image. A real image forms when light leaves an object and meets somewhere else. The object appears to be where its image is.
  147. 151. Images An image can be: <ul><li>enlarged, diminished or the same size
  148. 152. upright or inverted
  149. 153. real (light focusses there) or virtual (light looks like it focuses there). </li></ul>
  150. 154. Real Images A real image can be focussed onto a screen. The object appears to be where the image is. If it is bright and clear enough, a real image can trick the eye (and person) into thinking that something is really there. C F F Ray 1: Parallel to the principle axis and through the focus. Ray 2: Through the optical centre. Ray 3: Through the closest focus and then parallel to the principle axis. principle axis
  151. 157. Lens Calculations d o = distance from object to lens d i = distance from image to lens F = focal length C = centre of curvature = 2F
  152. 158. Convex Lens Summary object position Image position Real /virtual Enlarged / Diminished / same size Upright / Inverted Use (if any) Beyond C On C Between C and F On F Between F and the Lens
  153. 159. CAMERA Film/ CCD If the image were a very, very long way away, what would the distance from the lens to the film be?
  154. 160. Concave Lenses <ul><li>A concave lens is the opposite of a convex lens.
  155. 161. Light always diverges (spreads out).
  156. 162. Parallel light rays spread out as if they had come from a point called a focus.
  157. 163. Images will always be _______, ______,and ________.
  158. 164. Concave lenses will not be examined in IGCSE exams. </li></ul> This site explains lenses very well:
  159. 165. Alternate Names <ul><li>Convex lenses are also called converging lenses (because they converge light).
  160. 166. Concave lenses are also called diverging lenses.
  161. 167. Concave = “going into a cave”. </li></ul>
  162. 168. Parallel verses Non-Parallel Rays <ul><li>Objects from a long way away produce (virtually) parallel rays of light. Light rays from the sun can be considered parallel because its distance is considered to be ___________.
  163. 169. Parallel light rays converge at the __________. </li></ul>Objects nearby produce light rays which are not parallel. Light rays fro m an object of finite d o will meet at a distance d i . This distance can be found using a ray diagram or calculations. DON'T FORGET ARROWS!! sun
  164. 170. Lenses in IGCSE <ul><li>Only diagrams for convex lenses will be examined. </li></ul>
  165. 171. Answers
  166. 172. Crocodile Physics <ul><li>Try the “Lenses” exercise until it gets to concave lenses (try if you like). </li></ul>