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Flashcards

Waves

Holly Stokes-geddes Physics A-Level English 85 cards

Cards in this deck (85)

  1. 1What do waves do?Transfer energy from one place to another without any net transfer of matter
  2. 2Give an example of longitudinal wavesSound waves, ultrasound waves
  3. 3What are longitudinal waves like?The energy vibrates along the direction of the wave, perpendicular to the source
  4. 4Give an example of transverse waveselectromagnetic waves
  5. 5What are transverse waves like?They vibrate at 90 degrees to the direction of energy transfer
  6. 6What are progressive waves?Waves that move away from a source
  7. 7What are the two ways we can graphically represent waves?A 'snapshot' of the wave as it travels outwards; plotting displacement of the wave on the x axis and the distance from the source of the Y axis
    We can plot the oscillation of a particle against time. The particles will vibrate up and down so we plot displacement of the particle against time.
  8. 8What are the conditions for the amplitude of a wave to remain consistant?Energy is continuously transferred to that wave so it doesn't lose energy as it travels
  9. 9What is wavelength?The distance between two successive identical points that have the same pattern of oscillation. The distance from peak to peak.
  10. 10What is the period?The time taken to complete one full period of oscillation.
  11. 11What is the frequency of a wave?The number of oscillations per unit time. f=1/t
  12. 12What is the displacement of a wave?The distance moved from the source
  13. 13What is amplitude?The maximum displacement of a wave
  14. 14What is the phase difference?the relationship between the patterns of vibration at two points. Two points which have the same pattern of oscillation are said to be in phase because there is zero phase difference between them.
  15. 15What are waves known as if their ocsillation patterns are exact opposites?anti-phase!
    They are a half cycle different from each other
  16. 16What angle out of phase are waves in antiphase?pi radians
  17. 17How do we plot longitudinal waves on a graph?displacement against position
  18. 18What is the wave equation (VERY IMPORTANT ONE)Velocity = frequency x wavelength
  19. 19What is the speed of light?3 x 10^8 ms^-1
  20. 20What is the speed of sound?340 ms^-1
  21. 21what is the equation for powerenergy / time
  22. 22What is the eqauation of intensity?Power / area
  23. 23What is the relationship between amplitude and intensity?Intensity is directly proportional to amplitude squared
  24. 24What are ray lines used for?To simplify waves in diagrams. They are always drawn at right angles to the wavefronts.
  25. 25What happens to the wavelengths of waves when they are reflected?They don't change
  26. 26When does refraction occur?When a wave travels from one medium to another
  27. 27What two things can be observed when refraction occurs?The wave will change it's speed
    There may be a change in direction
  28. 28When using a ripple tank, what do the darker shadows show?The wave crests
  29. 29What kind of things can you adjust in a ripple tank?glass sheet to decrease water depth
    angles of waves
    obstacles or no obstacles
  30. 30What is diffraction?the spreading out of a wave after passing through an obstacle or gap
  31. 31When is diffraction most pronounced?When the wavelength of the wave being diffracted is the same size as the gap they are travelling through
  32. 32What process will occur if waves meet?interference
  33. 33What is interference?the addition of two or more waves (superposition) that results in a new wave pattern
  34. 34When can the interference of radio waves occur?when waves from the transmitter interfere with waves reflected off buildings
  35. 35What are the common properties of electromagnetic waves?They can all travel through a vacuum
    They have an electronic wave and a magnetic wave perpendicular to each other
    In free space they travel at the speed of light
    They are transverse
    They can all be reflected, refracted and diffracted
    They can all demonstrate interference
    They can be polarised
  36. 36What are all the waves on the electromagnetic spectrum (check out the table on page 221, it's super important)?Radio, microwave, Infrared, visible, UV, x-rays, gamma
  37. 37What is the actual difference between x-rays and gamma rays?X-rays are made from accelerated electrons outside the nucleus, and gamma rays are always emitted from the nucleus of an atom.
  38. 38Why can't radio waves ionise?They don't have high enough photon energy
  39. 39Why is ionising radiation dangerous to the bodyIt can lead to human cell mutations
  40. 40What are the three types of UV radiation?UV-A (99%, causes tanning)
    UV-B (causes sunburn and skin cancer)
    UV-c (filtered out by the atmosphere)
  41. 41What are the two waves that make up electromagnetic waves?electronic
    magnetic
  42. 42What is a plane polarised wave?A wave that has fields in only one plane
  43. 43What kind of waves can be polarised?Transverse waves ONLY because longitudinal waves do not oscillate at right angles to the direction of travel
  44. 44How do polarising filters work?They produce plane-polarised light by selective absorption of one component of the incident oscillations. The filter transmits only the component of light polarised perpendicular to that direction.
  45. 45What is malus' law?I = Imax . cos^2 a
    Therefore at 90 degrees no light will pass through and at 0 degrees maximum light will pass through
  46. 46Give an example of naturally occuring partially polarised light (light with more particles oscillating in one direction than another)When light has been reflected: light reflecting off a river, the blue light from the sky. These are because blue light is more easily scattered by dust particles and water vapor.
  47. 47How does strain analysis work?Some plastics such as the ones used to make rulers contain long chain molecules which can rotate the plane of polarisation. When placed between crossed polaroids, coloured images are produced that change when the material is stretched or squashed.
  48. 48What are the two things that tend to happen when refraction occurs?the wave will change speed
    the wave will change direction (unless it is travelling along the normal)
  49. 49In refraction, when will the speed of the wave DECREASE?when the wave moves from a lower to higher refractive index
  50. 50What is the equation for refractive index?refractive index = speed of light in a vacuum/speed of light in the material
    n = c/v
  51. 51What is the refractive index for light in a vacuum? in air? in water? glass? diamond?1
    1.00028
    1.333
    1.523
    2.41903
  52. 52What is Snells law?n1 . sin . I = n2 . sin . r
    The angles of incident and refraction are always measured from the normal
  53. 53In refraction, If the light speeds up when it enters the second medium, what happens to the angle of refraction?It gets bigger
  54. 54When does total internal reflection occur?when light travels from a medium of higher refractive index to lower, at less than the critical angle
  55. 55what else increases when you increase the angle on incidence?The angle of refraction
  56. 56What is the critical angle?The angle of incidence when the angle of refraction is 90 degrees
  57. 57What is the equation for the critical angle?sinC = 1 / n1 (if it involves air)
    or sinC = n2 / n1
  58. 58What does the principle of superposition state?when two or more waves of the same type meet, the resultant wave can be found by adding the displacements of the incident waves.
  59. 59What is constructive interference?The resultant wave is larger than the incident waves because they are in phase
  60. 60What happens (in superposition) when two waves are in anti-phase?They cancel each other - destructive interference
  61. 61What do we need in order to calculate a meaningful resultant using the principle or superposition?The waves need to have a constant phase difference, they must be coherent
  62. 62What is path difference?(referred to in wavelengths) The difference in distance travelled by two waves arriving at the same point
  63. 63What is the phase difference?(measured in radians) the difference in phases of two waves of the same frequency
  64. 64What does a path difference of a whole number mean?The waves will arrive at the same point in phase
  65. 65How can interference be demonstrated using sound waves?As you walk between two loudspeakers, there will be areas of destructive interference where the sound will be quieter and areas of constructive interference where the sound will be louder.
  66. 66How is interference demonstrated using microwaves?The wave is split into two separate paths in a wave tube. By adjusting the path lengths, you can create constructive or destructive resultant waves. (diagram on page 234)
  67. 67What two conditions have to be satisfied in order to measure the wavelength of light?The light must be monochromatic
    There must be an accurate method of producing very small path differences
  68. 68What did young do?used a monochromatic red light source which he placed in front of a piece of black card with a narrow slit, X (to make the wave coherent). In front of this was another piece of card with two slits, Y. Lights from the two slits interfere to create a wave pattern on the beard behind.
  69. 69What is the equation for working out the wavelength of a light source (Youngs double slit experiment)?wavelength = ax/D
    a is the distance between the slits
    x is the distance between the fringes
    D is the distance between the screen and the slits
  70. 70What is a diffraction grating?A thin piece of optical equipment made of glass that has thousands of tiny grooves created by a diamond. Light shone through it will be diffracted.
  71. 71Why is it difficult to obtain wavelengths accurately using Young's model? and how is this overcome?The diffraction fringes are quite blurred
    It is overcome by using multiple slits
  72. 72In a diffraction grating, what is the affect of having more 'slits'?It improves the brightness and sharpness of the maxima and makes it easier to measure an accurate value for wavelength. The maxima will also be further apart.
  73. 73what is th equation for a diffraction grating?n(wavelength) = dsina
    n is the order of the maxima
    wavelength is the wavelength of the incident monochromatic light
    d is the separation of the slits
    a is the angle the beam makes with the grating
  74. 74when are no further maxima observed and how can this help you answer questions on the diffraction gratingwhen
    n(wavelength) / d
    is bigger than one
    because sina can't exceed 1
    This is useful because if asked how many maxima there are, just divide the distance between the slits by the wavelength
  75. 75What is a stationary wave?A wave who's energy is confined to a fixed position
  76. 76How are stationary waves formed?(Diagrams in figure 3)
    -Two waves in antiphase (phase difference of pi) move toward each other and cancel out
    -A fraction of a second later, both waves have moved a little and are now in phase which creates a larger wave
    -This switches continuously, in phase, out of phase, in phase...and so on
  77. 77What are nodes and antinodes?Nodes are points in a stationary wave at which there is no displacement of particles at any time.
    At antinodes, the displacement of the particles varies by the maximum amount.
  78. 78How do we measure stationary waves using microwaves?A microwave generator projects microwaves at a metal sheet. Place a microwave detector in the middle and when you move it along the stationary wave, the microwave signals will be particularly strong every half wavelength.
    If you multiply the frequency of the microwaves by the measured wavelength values from the stationary wave, you can work out the speed.
  79. 79What is the frequency of vibrations on a string governed by?It's mass per unit length
    It's tension
    The length of the string
  80. 80How are stationary waves created on a string?The string is plucked and a wave travels down it. When it reaches the end it is reflected back and the two waves interfere to create a stationary wave.
  81. 81What is the fundamental mode of vibration?The length of the string is half the wavelength of the note.
  82. 82What are the other harmonics in relation to the fundamental mode?Whole number multiples of the frequency of the fundamental mode
  83. 83How can we create a stationary longitudinal wave?By blowing accross one end of the tube, pushing the air down it.
    (diagram on page 247)
  84. 84For stationary waves in a tube, what is the relation between displacement and air pressure?A node for displacement will be an antinode for air pressure and so on.
  85. 85Why are stationary waves still formed in open tubes?Waves are still reflected from the open ends. because of this, each end is an antinode (see diagram page 247)

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A-Level Physics Flashcards on Waves, created by Holly Stokes-geddes on 12/08/2016.
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  • Created by Holly Stokes-geddes · Jul 15, 2016
  • Copied by Holly Stokes-geddes · Aug 12, 2016
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