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P8.3 Flashcards

1
Q

What is the history of the model of the universe?

A
  • 400BC Aristotle = Earth was centre of universe
  • 100AD Ptohamy = Earth centre model and universe was surrounded by fixed unchanging stars
  • 1543AD Copernicus = Sun centred model
  • 1609AD Galileo = Stars changed and not all object orbit Earth
  • 1687AD Newton = theory of gravity confirms sun-centric model
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2
Q

Why did ideas about the universe change?

A
  • they have changed as observations have been made and create thinking occurred to explain the observations
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3
Q

What is red shift?

A
  • when source moves away from you the wavelength of the light it emits increases and the frequency decreases = this is red-shift
  • if the source moves faster, the red shift is bigger
  • if the source if moving towards you, the light is blue shifted
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4
Q

Who proposed the idea of red shift?

A
  • 1929 - Erwin Hubble measured the speed of galaxies from the absorption spectrum of the light they emit
  • Hubble used red-shift to work out that galaxies were moving away from us and that the more distant a galaxy is, the faster it is moving away
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5
Q

What evidence is there that the universe is expanding?

A
  • Different chemical elements absorb different frequencies/ wavelength of light
  • Each element produces specific pattern of dark lines at the it frequency absorbs in the visible part of the EM spectrum
  • light from distant galaxies = see same patterns but at a slightly lower frequency/higher wavelength
  • observed increase in wavelength of light coming from the galaxy = the light is shifted towards the red end of the spectrum = light is red-shifted
  • measurements of Redshift suggest that all distant galaxies= moving away from us & each other very quickly and it’s the same result in every direction
  • more distant galaxies = greater Redshift than near ones (bigger observed increase in wavelength)
  • More distant galaxies are moving away faster the new ones = universe is expanding
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6
Q

What is the Big Bang theory?

A
  • Universe started as something very dense and tiny (smaller than an atom) which underwent sudden expansion 13.7m yrs ago
  • Big band model = space between the galaxies is expanding and we aren’t at the centre of the universe
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7
Q

What is cosmic microwave background radiation? (CMBR)

A
  • discovered in 1960s
  • low frequency microwave radiation came from all directions and all parts of the universe
  • scientists worked out this radiation was left over from the Big Band itself
  • very high energy and high frequency radiation has been stretched over time so it’s now in the microwave region of the spectrum
  • as universe expands and the cools the background radiation drops in frequency
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8
Q

What evidence suggests that the universe started with a bang?

A
  • galaxies are moving away from each other at great speed, suggesting that something got them going in the first place (big bang theory)
  • initially all matter in universe occupied a single point
  • this single point exploded (Big Bang)
  • space started expanding and expansion is going on
  • CMBR is leftover energy of this initial explosion and redshift proves it’s still expanding
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9
Q

What is the model of our Solar system now?

A
  • sun (star), planets (spherical objects in orbit around sun), moon (orbits around planets), minor planets (comet in orbit around sun, asteroids, dwarf planets) and comets (made of ice and dust that orbit the sun)
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10
Q

Describe the inner planets in our solar system

A

Inner = mercury, Venus, Earth , Mars (rocky and have an atmosphere

  • mercury and mars have very thin atmospheres
  • Venus has an atmosphere that’s mainly CO2 and rains sulfuric acid
  • Earth = 1 moon, Mars = 2 moons and Venus &Mercury = no moons
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11
Q

Describe the inner planets in our solar system

A
  • Jupiter, Saturn , Uranus and Neptune
  • Jupiter and Saturn = gas giants
  • Uranus and Neptune = ice giants and all of the, have lots of moons and all have rings
  • asteroid belt between Mars and Jupiter = pieces of rock left over from formation of the solar system and also has a dwarf planet, Ceres
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12
Q

How was the Sun formed?

A
  • Sun formed from a huge cloud of dust and gas put together by gravity
  • As this happened the core got very hot and eventually particles move fast enough for nuclear fusion to occur (joined together)
  • Balance between gravity pulling particles inwards and expansion of hot gases outwards means that the Sun is stable right now
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13
Q

In the life cycle of stars, how are they formed?

A
  • huge gas clouds (mainly hydrogen) called a nebula begins to be pulled together by gravity
  • large ball of gas forms at the centre of the cloud
  • as it gets more denser = more gas is pulled in, ball gets hotter and forms a PROTOSTAR
  • protostar continues to use to grow larger until nuclear fusion occurs to form a helium nuclei, giving out massive amounts of energy = star is born
  • star enters period of equilibrium as the energy releases by nuclear fission results in outward pressure which tries to expand the star, and is balanced by the force due to gravity pulling onwards (gravitational collapse) = this is the the stable part of the lifecycle and called the main sequence star phase and it lasts several billions years (sun is in the middle of it)
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14
Q

In the life cycle of stars, how do small to medium stars die?

A
  • death depends on mass of a star so if small (Sun):
  • as hydrogen core runs out, the fusion of heavier elements occur and the stars swell up and turns red as the surface cools = RED GIANTS
  • it becomes unstable and ejects its outer layer of the dust and gas and so the star breaks away and forms a PLANETARY NEBULA
  • this leaves just the hot dense solid core of the star, called WHITE DWARF
  • this cools over time and fades away
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15
Q

In the life cycle of stars, how do large stars die?

A
  • large stars expand and cool but grow larger to form RED SUPERGIANTS
  • starts to glow brightly again as they undergo more fusion and expand and contract several times = forming even heavier elements in various nuclear reactions
  • when they run out of fuel, they collapse into themselves called a SUPERNOVA
  • the exploding supernova causes the centre of the star to be crushed by immense gravitational forces to form a very dense star made of neutrons = NEUTRON STAR (spins very fast and sends pulses of radiowaves to Earth which we can detect)
  • or if the star is big enough, it will form a BLACK HOLE
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16
Q

How do black holes form?

A
  • When very large stars collapse after a supernova, the core can be crushed down into a very tiny space, forming a black hole
  • a super dense point in space that the forces of gravity these are so immense that not even light can escape
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17
Q

What do stars form in their lifecycle?

A
  • small- medium = cloud of dust and gas (nebula), protostar, main sequence star, red giant, planetary nebula, white dwarf
  • large - very large = cloud of dust and gas (nebula), protostar, main sequence star, super red giant, supernova, neutron star or if very big = black hole
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18
Q

What are the two types of satellites?

A
  • Artificial satellites = sent by humans to orbit objects like the Sun or planets
  • Natural (moon) = made from same material as rest of the objects in the Solar system
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19
Q

What are the two types of orbits we use for the satellites around the Earth?

A
  • Geostationary orbit - appear to be in same position above the Earth’s surface
  • Low polar orbit - travel over different parts of the Earth’s surface in each orbit
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20
Q

Describe satellites in the geostationary orbit:

A
  • high orbit over the Earth’s equator - 36,000 km above Earth’s surface
  • orbit once every 24 hours
  • they stay above at the same point as they Earth’s surface rotates with them
  • ideal for communications - telephone, TV, radio as they stay at the same point so it’s easy to point transmitters and receivers at them
  • can transfer signals from one side of Earth to other in a fraction of a second
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21
Q

Describe satellites in the polar orbit:

A
  • sweep low over both poles whilst the Earth rotates beneath them
  • takes 2 hours for each orbit as really quickly
  • much closer to the earth (2000km) so move faster
  • can scan the next bit of the globe each orbit, allowing the whole surface of the Earth to be monitored each day
  • used for weather, military (spy), mapping and surveillance
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22
Q

What is a stable orbit?

A

When an object is moving at the right speed for the distance from the object it orbits (e.g planets)

  • must be moving at just the right speed as if too fast it would fly off into space and if too slow, it would spiral down and crash into whatever it was orbiting
  • if object’s speed changes then radius of its orbit must also change to keep it stable
23
Q

What is the shape of the orbits of the planets around the Sun?

A
  • Almost circular
  • object travelling in a circle = constantly changing direction and so velocity is constantly changing so it’s accelerating (speed is not changing as it doesn’t have a direction)
24
Q

What force causes objects to orbit?

A
  • for object to accelerate = must be a force acting on it
  • object moving in circle = force is directed towards the centre = centripetal force
  • orbiting objects = force is provided by gravity
  • gravity could cause the object to just fall towards what it’s orbiting but as it’s already moving, it just causes it to change its direction
  • object keeps accelerating towards what its orbiting but it’s velocity is at right angles to the acc so it keeps moving in a circle
25
Q

What happens to the speed when you get closer to an object?

A
  • closer you get to star or planet, the stronger the gravitational force is
  • stronger the force the, the faster the orbiting object needs to be going to avoid falling into what it’s orbiting
  • so the closer you get the faster you need to go to stay in orbit
26
Q

What happens when an object in a stable orbit starts moving faster or slower?

A
  • for an object in the stable orbit, if its speed changes, the size (radius) of its orbit must do so too
  • if an object moves faster, the radius must get smaller
  • if object moves slower, the radius must get larger
27
Q

What would happen if Neptune sped up or slowed down?

A
  • if Neptune sped up then the gravitational force would be too small to keep it in orbit and it would fly off
  • if Neptune slowed down then it can’t maintain the fixed orbit and accelerates towards the Sun as the pull of gravity is stronger than the force pushing outwards
28
Q

What emits radiation?

A

All objects

- intensity needs wavelength distribution depends on the object’s temperature

29
Q

What is intensity?

A
  • power per unit area ( y - axis)
  • y axis on graph shows how much energy each wavelength of emitted radiation transfers to a given area in certain amount of time
30
Q

What happens to the intensity of every emitted wavelength when temperature increase?

A
  • the intensity also increases
  • intensity increases more for shorter wavelengths than longer wavelengths (because shorter wavelengths of EM radiation transfers more energy)
  • this causes the peak wavelength (most common wavelength) to decrease
31
Q

What happens to the peak wavelength as objects get hotter?

A
  • peak wavelength gets shorter and the intensity-wavelength distribution becomes less symmetrical
32
Q

What is the peak wavelength of most objects?

A
  • IR region

- so most objects emit IR (some emit visible light too - filament bulb/glowing light)

33
Q

What type of radiation is emitted by objects?

A
  • warm objects emit IR radiation high we can detect with a thermal imaging camera
  • type of radiation emitted depends on temp of object = hottest is bluish white, hot is yellow and cooler is red
  • hotter objects emit more radiation at a higher frequency and lower wavelength
  • less radiation means less frequency and high wavelength
34
Q

What does the radiation of hot stars look like?

A

Light from stars can be analysed

Hot stars = higher frequency and higher intensity

35
Q

What happens if an object emits the same amount or radiation as it’s absorbing?

A
  • it would be a constant temperature
36
Q

What happens if an object emits more radiation than it’s absorbing?

A
  • so the object is hotter than its surroundings so over time it cools down
  • cup of tea = gives out more IR radiation than absorbed so it cools down
37
Q

What happens if an object emits less radiation than it’s absorbing?

A
  • if it’s colder than its surroundings (absorbs more than emits) = over time the object warms up
  • ice cream on a hot day
38
Q

What type of radiation does the Sun emit?

A
  • UV, IR and visible light
39
Q

What happens when the Sun’s rays reach the Earth?

A
  • some reflects off the Earth’s atmosphere, some is absorbed by the atmosphere (UV and IR) and some passes through to reach Earth (some UV, IR and light)
40
Q

What does the overall temperature of the Earth depend on?

A
  • it depends on the amount of radiation it reflects, absorbs and emits
  • during the day, lots of radiation is being absorbed, causing an increase in local temperature
  • at night, less radiation is absorbed than is emitted, causing a decrease in the local temperature
  • overall, the Earth’s temperature stays fairly constant (one side is absorbing while other is emitting)
41
Q

How is some of the radiation absorbed by the Earth re- emitted from the Earth?

A
  • some of this re- emitted radiation is absorbed by gases in the atmosphere like CO2. These gases re-emit this radiation in all directions, including back towards Earth (greenhouse effect = helps keep Earth warm)
  • greenhouses gases increase so absorb IR radiation that should be emitted into space and reflect it back to Earth’s surface
  • in theory temp is constant but it greenhouse gases change, the temp changes
42
Q

What can changes in the atmosphere lead to?

A
  • can change the Earth’s temperature (e.g increasing CO2 levels in the atmosphere increase the amount of radiation the atmosphere absorbs, contributing to global warming)
  • atmosphere still affects radiation that passes through it (e.g visible light gets refracted by water droplets’)
43
Q

What is the structure of the earth?

A
  • inner core = solid
  • outer core = liquid
  • mantle = almost entirely solid but flows out
  • shallow crust = solid
44
Q

Why can’t we just drill into the core?

A
  • it’s too hot and too deep
45
Q

How can we used waves to explore structures we can’t see?

A
  • waves can be reflect (partially/ completely if it can’t travel through the material
  • can be refracted (travel at diff speed)
  • can be absorbed
  • by studying where waves are detected/ not detected (absorption/reflection) and change of speed/direction we can find our structures
46
Q

What kind of waves does sonar use?

A
  • sound waves
47
Q

Why and how is sonar used?

A
  • used to measure the depth of seabed/ detect things in ocean (e.g submarine )
  • transmitter and receiver on boat send out and detect pulses of sound waves and when sound reaches a boundary (seabed and sea), they are reflected back towards boat
  • by timing how long the reflected waves take back to return the distance to seabed/ object can be calculated
48
Q

What kind of waves do earthquakes produce?

A
  • seismic waves which travel through the Earth and are detected all over the surface by using seismometers
  • seismograms record the arrival and intensity of 2 types of seismic paves (P and S) and the height of the line = intensity
49
Q

What are seismic waves like?

A
  • when they reach a boundary = some are reflected
  • waves change speed as the properties of the earth change (refract)
  • most times the waves change speed gradually, resulting in a curved path but the properties change suddenly, the wave speed changes abruptly, and the path has a kink
50
Q

What are the two main different types of seismic waves?

A
  • P waves
  • S waves
  • near the epicentre of an earthquake (origin) both are detected
51
Q

What are the properties of S waves?

A
  • transverse and can travel through solids
  • slower than P waves
  • don’t reach the other side of the Earth of the epicentre as they can’t pass through the liquid outer core
52
Q

What are the properties of P waves?

A
  • longitudinal waves that travel through solids and liquids
  • faster than S waves
  • they refract slowly as the density of the mantle changes and then refract sharply at the boundary between the mantle and the core and therefore can reach other side of Earth of the epicentre, but don’t reach all the way as some gaps as they spread out
53
Q

What are shadow zones?

A
  • regions of the Earth where P- waves are found but no S - waves, or S-waves found but no P- waves or neither found
  • this is due to their different abilities to travel through solids and liquids
54
Q

How did we work out the structure of the Earth?

A
  • 1914, Bruno Gutenberg = started that if P waves can travel through the core then it must be a liquid (outer core)
  • 1936, Inge Lennmann = analysed O-waves and worked out the centre (inner core) is solid
  • by analysing seismic waves = worked out the sizes of the inner and outer core

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