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eecavendish Physics GCSE English 129 cards

What does diffraction through a circular aperture look like?

Cards in this deck (129)

  1. 1What is a solar day?The time that passes between the sun appearing at its highest point in the sky on two successive days
  2. 2Why does the moon take longer than 24 hours to return to the same position in the sky?Because the earth is rotating and the moon is orbiting the Earth
  3. 3What is a sidereal day?The time taken for a star to be seen in the same position in the sky - the time taken for the Earth to spin 360 degrees
  4. 4How long is a sidereal day?23 hours 56 minutes 4.09 seconds
  5. 5Why is a sidereal day a different length to a solar day?Because whilst the Earth takes a sidereal day to turn 360degrees, it has also moved relative to the sun which means it takes longer for the sun to be seen in the same position
  6. 6How do we see the moon?It reflects the sun's light
  7. 7What are the phases of the moon?The different shapes that are seen as the moon reflects more, or less, light towards the Earth depending on the angle
  8. 8How many days does it take for the moon to orbit Earth?27.3
  9. 9What is a lunar month?The time between each full moon - 29.5 days
  10. 10How large is the diameter of the moon?1/8 the diameter of Earth
  11. 11Why do the Sun and the Moon appear to be the same size from Earth?The Sun's diameter is 400 times bigger than the Moon's BUT the Sun is 400 times further away than the moon
  12. 12What occurs during a solar eclipse?The Moon passes between the sun and the Earth, casting a shadow on the Earth
  13. 13What occurs during a lunar eclipse?The Moon travels into the Earth's shadow so cannot reflect the Moon's light - it is not visible from Earth
  14. 14What is an umbra?An area of total shadow (e.g. directly behind the Earth on the opposite side to where it is facing the Sun)
  15. 15What is a prenumbra?An area of partial shadow
  16. 16Why is there not a solar or lunar eclipse every month as we would expect?The Moon's orbit is at a different angle to the Earth's orbit around the sun - eclipses only occur when they line up which is a rare occurrence
  17. 17The amount of light that a planet reflects to Earth depends on which four factors?- How close the planet is to the Sun
    - How close the planet is to Earth
    - Size of planet
    - Nature of planet's surface
  18. 18What is retrograde motion?When a planet appears to take a backwards route across the sky
  19. 19Why was the Earth-centred model of the universe problematic?It couldn't explain the movement of planets (retrograde motion) or the variation in brightness
  20. 20Why does retrograde motion occur?The Earth moves/orbits faster than planets further away from the Sun - as Earth overtakes them they appear to move backwards
  21. 21What are constellations?Patterns in the stars
  22. 22Why do we see different stars in the summer from the winter?The Earth has moved to the other side of its orbit
  23. 23What is the declination in terms of locating a star?The height of the star above the equator in the sky
  24. 24What does a negative declination mean?That the star is south of the equator
  25. 25What would be the declination of a star directly above the equator?0 degrees
  26. 26What is the right-ascension in terms of locating a star?The angle that defines the direction (east/west) in which to look
  27. 27When taken together, what do the declination and the right ascension provide?A coordinate system for locating or describing the location of a star
  28. 28What is the celestial sphere?A reference for the coordinate system of stars - an imagined dome that surrounds the Earth made up of all the light from astronomical objects
  29. 29Where is the declination measured from in the celestial sphere?From the celestial equator (directly over the Earth's equator)
  30. 30What is the declination measured in?degrees, minutes and seconds
  31. 31What is the equivalent of one minute (1`) in degrees?1/60 of a degree
  32. 32What is the equivalent of one second (1``) in minutes?1/60 of a minute
  33. 33What is the name given to the plane of the Earth's orbit?The ecliptic - this is the path of the Sun during the year
  34. 34Where is the right ascension measured from in the celestial sphere?The point where the Sun moves to the northern hemisphere
  35. 35What is the vernal equinox?The point where the Sun moves into the northern hemisphere
  36. 36What is the right ascension measured in?hours, minutes and seconds
  37. 37What is the equivalent of 1 hour in degrees?The celestial sphere rotates with Earth once every 24hrs, so 24hrs = 360degrees
    Therefore, 1hr = 15degrees
  38. 38What is the speed of light through a vacuum?300 million m/s
  39. 39What does the speed of light depend on?The substance (medium) in which it is travelling
  40. 40What is refraction?The change of direction and slowing down of a wave as it enters a different medium
  41. 41What do convex lenses do?Bring light rays together at a focal point
  42. 42What is focal length?The distance from the lens to the focal point
  43. 43What happens to the focal length of a lens as the power increases?It decreases - powerful lenses have a shorter focal length
  44. 44What is the unit for power? (Of a lens)Dioptres
  45. 45What is the formula for the power of a lens?Power = 1/focal length(m)
  46. 46What happens to the focal point if the incoming light is not parallel to the principal axis through the centre of a lens?The focus will be away from the axis
  47. 47What are extended objects?Objects that look larger than a point
  48. 48Give at least two examples of extended objectsthe Moon, the Sun and galaxies
  49. 49What do ray diagrams show?How and where an image can be formed as light rays hit a lens
  50. 50What happens to a ray that hits the lens parallel to the axis?It is refracted through the focal point
  51. 51What happens to a ray that travels through the focal point?It is be refracted parallel to the axis
  52. 52What happens to a ray that hits the centre of a lens?It is be undeviated - does not refract
  53. 53What are the names of the two convex lenses that are used to make a simple telescope?Objective lens and eyepiece
  54. 54Describe the focal lengths of the objective lens and the eyepieceObjective lens - long focal length (low power)
    Eyepiece - short focal length (high power)
  55. 55How are the lenses placed in a simple telescope?They are placed so that the length of the telescope is the sum of their focal lengths
  56. 56Why does the objective lens need a larger diameter?To collect more light and make a brighter image
  57. 57What does the eyepiece do?Magnify the image to allow the human eye to see the image formed by the objective
  58. 58What is the overall effect of the telescope in terms of light rays?It increases the angle between the light rays and the axis of the telescope, magnifying the image
  59. 59What is the formula to calculate magnification?magnification =
    (focal length objective)/(focal length eyepiece)
  60. 60What structure receives light in a reflecting mirror?A concave mirror
  61. 61What effect does a concave mirror have on parallel light rays?It reflects the light rays, making them converge at a focal point
  62. 62What is the role of the secondary mirror in a reflecting telescope?It reflects the light rays into an eyepiece
  63. 63What is chromatic aberration?The production of an image with coloured edges by a refracting telescope with a lens too large - the different wavelengths refract different amounts
  64. 64Why are reflecting telescopes better than refracting telescopes?Refracting telescopes need large lenses which are difficult to manufacture, such lenses will be heavy, chromatic aberration occurs
  65. 65What is diffraction?The effect when waves spread out after passing through a gap or around an obstacle
  66. 66When is diffraction greater?When the gap or obstacle is the same size as the wavelength of the wave
  67. 67Which two factors does the diffraction of a wave depend on?The wavelength of the wave and the diameter of the gap/obstacle
  68. 68What happens to the diffraction as the wavelength increases?The effect increases - waves with a longer wavelength diffract more
  69. 69What is an aperture?An objective lens or objective mirror
  70. 70If diffraction causes the light from two stars to blur together an appear as one star, what is this image described as?Unresolved
  71. 71How can we improve the resolution (reduce the diffraction) of an image?By having a wider pupil or using a telescope with a bigger diameter aperture
  72. 72What does diffraction through a circular aperture look like?What does diffraction through a circular aperture look like?
  73. 73How can we form a spectrum of visible light?By passing light through a glass prism
  74. 74What two things can a spectrum tell us about the light source?The temperature and the chemical composition
  75. 75What is a diffraction grating?A reflective plate with lots of closely spaced lines drawn on (e.g. a CD)
  76. 76How does a diffraction grating produce a spectrum?Light reflects from the plate and different wavelengths diffract at different amounts - they are visible from certain angles and produce a spectrum
  77. 77Why are diffraction gratings more effective than prisms at producing spectra?It produces a more evenly spread spectrum and less light is wasted
  78. 78What is a quasar?A highly redshifted and powerful object in the solar system, believed to be matter falling into a black hole
  79. 79What two measurements are needed in order to find the distance to a star?- Position of a star compared to a distant star measure twice (readings six months apart)
    - The parallax angle (using above readings)
  80. 80What can we say about stars with larger parallax angles?They are closer to Earth
  81. 81What are parallax angles measured in?seconds of an arc (")
    often referred to as arcseconds
  82. 82What is a the unit of length defined by using the parallax shift of a star?The parsec
  83. 83What is the formula for calculating the distance to a star in parsecs?distance (parsecs) =
    1/parallax angle(seconds)
  84. 84Why can parallax calculations only be used for nearby stars?The parallax angles of distant stars are too small to measure
  85. 85What is the equivalent of 1parsec in light years?1pc = 3.26 light years
  86. 86What is the luminosity of a star?The total power emitted by a star
  87. 87Which two factors does luminosity depend on?The radius of the star (larger surface area, more radiation emitted)
    The surface temperature (hotter = more radiation)
  88. 88Why do further stars look fainter?The radiation spreads out as it travels through space
  89. 89What is a variable star?A star that changes its brightness
  90. 90What is meant by the period of a variable star?The time taken for a variable star to complete one cycle of brightness change
  91. 91What is a binary star?A star that is orbited by a dimmer partner
  92. 92What are Cepheid variable stars?Large, pulsating stars with a brightness that changes in a predictable way
  93. 93What is a standard candle?An object of known brightness
  94. 94How can we use Cepheid variable stars as standard candles to work out how far away they are?There is correlation between the period and luminosity of a Cepheid variable. We can measure the period to find the luminosity and compare this measurement to how much light we receive on Earth. We can then work out the distance.
  95. 95What did Harlow Shapley's method of measuring galaxies involve?Using Cepheid variable stars to work out distances to globular clusters. Using the assumption all clusters are same size/brightness, can work out distances.
  96. 96What are nebulae?Fuzzy, bright patches of light observed by telescopes
  97. 97Why did Curtis and Shapley disagree about the nature of nebulae?Curtis - nebulae are other galaxies like our own
    Shapley - our galaxy formed the whole universe, nebulae are clouds of gas
  98. 98What is Hubble's Law?speed of recession(of galaxies) (km/s)=
    Hubble constant multiplied by distance (Mpc)
  99. 99What process provides the energy source in stars?Nuclear fusion
  100. 100What happens to the photons of gamma radiation that are released in nuclear fusion?They travel outwards, interacting with atoms throughout the radiation zone and losing energy as they go
  101. 101What is a photosphere?The surface of a star
  102. 102What type of spectrum is produced when light from flaming substances is put through a prism?An emission spectrum - a unique set of coloured lines
  103. 103What type of spectrum is produced when bright white light is shone through the vapour from an element?An absorption spectrum - a spectrum formed with dark lines where the atoms in the element have absorbed some of the wavelengths from the light
  104. 104Explain how spectra can reveal the temperature of a starIonising radiation produces ions - astronomers can tell which atoms have been ionised and this gives a measure of temperature
  105. 105When is light emitted from an atom?When an electron loses energy - it drops from a higher energy level to a lower one
  106. 106Explain what is meant by absolute zeroThe point where all molecules in a substance stop moving - the temperature can not get any lower
  107. 107Describe the relationship between volume and temperature of a gasThere is a linear relationship - volume increase as temperature increases but it is not direct proportionality because the line would not go through the origin
  108. 108What is the Kelvin?A unit of absolute temperature
  109. 109What is absolute zero in Kelvin?-273K
  110. 110How do you convert a temperature in Celsius to Kelvin?add 273
    e.g. 20degrees C =
    20 + 273 = 293K
  111. 111Describe the relationship between volume and absolute temperatureVolume is directly proportional to absolute temperature
  112. 112What is Boyle's law about the relationship between the pressure and the volume in gases?pressure multiplied by volume = constant
  113. 113What are the three gas laws?pressure/temperature = constant at constant volume
    volume/temperature = constant at constant pressure
    pressure times volume = constant at constant temperature
  114. 114What is a protostar?A dense mass of dust and gas pulled together by gravity which attracts more substances from the universe until a new star is formed
  115. 115What is inside the Sun's core at a very high temperature?A plasma of electrons and nuclei whizzing around
  116. 116What happens when two protons collide during nuclear fusion?They form a deuterium nucleus (a heavy form of hydrogen)
  117. 117Why is the high speed of protons important for nuclear fusion to take place?Ordinarily two protons would repel each other as they are both positively charged - the high speed allows them to overcome the electromagnetic repulsion
  118. 118Name the three isotopes of hydrogenHydrogen - 1 proton
    Deuterium - 1 proton + 1 neutron
    Tritium - 1 proton + 2 neutrons
  119. 119What is a positron?An anti-matter equivalent of the electron - same mass but positively charged
  120. 120What is a neutrino?A very low mass, neutral particle
  121. 121What is meant by charge conservation in nuclear reactions?The charges are the same before and after the reaction
  122. 122What happens to the 'missing' mass in a reaction to make deuterium?It is lost as it turns into energy
  123. 123What is Einstein's energy equation?E = mc2
    e=energy released
    m=mass(kg)
    c=speed of light
  124. 124What is the main sequence of a star and what does it involve?The longest phase of a star's life where it fuses hydrogen into helium
  125. 125What is a supergiant?A star that emits a lot of energy per second and is so hot it glows blue
  126. 126What is a yellow giant star?Cooler than our sun but over 200times more luminous
  127. 127What is a white dwarf?Emits a lot of UV radiation, same mass as the sun but same size as Earth
  128. 128What happens to a star when the hydrogen is running out?There is helium core surrounded by a layer of hydrogen that fuses. This releases energy which makes the surface expand making the star appear red - it is a red giant.
  129. 129Why do stars explode in supernovas?Once there is no more hydrogen and all energy has been used to create heavier elements there is nothing left to oppose gravity

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GCSE Physics Flashcards on P7, created by eecavendish on 16/06/2014.
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