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Science > P7 > Flashcards

P7 Flashcards

0
Q

Solar day

A

The time taken for the sun to return in the same position in the sky. Takes 24 hours.

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1
Q

Sidereal day is?

A

Time taken for a star to return to the same position in the sky. It’s about 23 hours and 56 minutes.

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2
Q

How long does it take for the moon to return to the sky?

A

Takes about 25 hours to return in the same position in the sky.

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3
Q

Why does a solar day take longer than a sidereal day?

A

Because the Earth or its the sun in the same direction it spins, so the Earth needs to spin more than 360 degrees before the sun returns at the same position in the sky.

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4
Q

What are the two main faces of the moon?

A

The full moon and the new moon.

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5
Q

Explain a lunar eclipse.

A

During orbit the moon sometimes passes through the Earth’s shadow. So little light is reflected from the moon.

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6
Q

Explain a solar eclipse.

A

The Moon, Earth an Sun line up. The Moon can block out the Sun.

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7
Q

Why don’t eclipses happen very often?

A

The Moon orbits at an angle to Earth’s orbit around the Sun.
So most of the time the Sun,Moon and Earth don’t line up very often.
Even when there is a solar eclipse only s very small region of Earth can see it.

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8
Q

When astronomers measure the sky what two fixed positions do they measure from and what are the two angles used to measure the positions in the sky?

A

The two fixed positions astronomers are:
The pole star-Star directly above North Pole and doesn’t seem to move.
The celestial equator-Imaginary plane running across the sky out from the Earth’s equator.

The two angles used to measure positions in the sky are:
Declination-measured in degrees.
Right ascension- measured in degrees or time.

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9
Q

What speeds do different planets orbit the sun and in what direction?

A

All planets orbit the sun in the same direction, the closer to the Sun, the quicker the planet.

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10
Q

What is the retrograde motion?

A

The retrograde motion only happens to the outer planets, every so often a planet seems to change direction and go the other way a bit. It happens because both the planet and Earth are moving around the sun, so we’re seeing the motion of the planet relative to Earth.

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11
Q

Refraction

A

When a wave hits a medium at an angle, part of the wave hits the boundary first and slows down while the other part carries on at the first, faster for a while. So the wave changes direction.

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12
Q

Explain how a convex lens converges light.

A

As the light ray hits the surface of the lens and passes from air to grass, it slows down and causes the light to bend towards the ‘normal’. When it hits the glass to air boundary on the other side it speeds up and bends away from the normal, making them all converge to a focus point.

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13
Q

Explain how a triangular prism can refract light to form a spectrum.

A

A triangular prism does not have parallel boundaries, which means the different wavelengths don’t recombine, and you get a rainbow effect.

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14
Q

Convex lens

A

One that gets fatter towards the middle.

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15
Q

What is the focal point?

A

Where the rays initially parallel to the principal axis meet.

And the focal length is distance from the middle of the lens to the focal point.

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16
Q

The powerful the lens the more powerful the what?

A

The more powerful the lens the more strongly it converges light, so shorter the focal length.

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17
Q

Power(D)=

A

1
—————-
Focal length(m)

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18
Q

Explain how a simple refracting telescope works.

A

1) It has an objective lens and a more powerful eye lens.
2) The objective lens collect all the light from the object being observed and forms an image of it, and they eye piece magnifies it so we can view it.

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19
Q

What factors have to be done so a simple refracting telescope works?

A

The lenses have to aligned on the same principle axis and their focal lengths are in the same place.

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20
Q

Magnification=

A

Focal length of objective lens(Fo)
= ———————————————-
Focal length of eye lens (Fe)

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21
Q

How does a concave mirror work?

A

Parallel rays of light shinning on a concave mirror reflect and converge.

By putting an eyepiece near the focal point you can magnify the image.

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22
Q

Explain how you find the focal point of a concave mirror.

A

The concave mirror is like a portion of a sphere, the centre of the sphere is the centre of curvature,C.

The centre of the mirror’s surface is called the vertex.

Halfway between the centre of curvature and the vertex is the focal point, F.

Halfway

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23
Q

What is diffraction?

A

All waves spread out(diffract) at the edges when the pass through gap or past an object.

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24
Q

What does the amount of diffraction depend?

A

The amount of diffraction depends on the size of the gap relative to the wavelength of the wave.

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25
Q

Explain why it is important that astronomers use objective lenses with huge apertures ?

A

The aperture is the diameter of the lens.

The bigger the aperture, the more radiation can get into the telescope and the better the image formed.

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26
Q

What is one of the reasons that astronomers use big concave mirrors over big objective lenses?

A

Making big mirrors is much cheaper and easier to make accurately.

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27
Q

Explain how a diffraction can be used to make a spectrum.

A

A diffraction grating has very narrow slits, when whit light passes through the gaps in diffraction grating, the different wavelengths of coloured light are all diffracted by different amounts.

This creates a spectrum of different coloured light.

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28
Q

What do astronomers use diffraction grating for?

A

They use the spectra made to analyse the light coming from the stars.

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29
Q

Luminosity

A

How bright something is if you were right next to it.

30
Q

What does the luminosity of a star depend on?

A

Depends on it’s and temperature.

31
Q

Observed intensity/ observed brightness

A

The luminosity of to from where you are.

32
Q

What is a Cepheid variable?

A

Cepheid variables pulse on brightness.

The greater the luminosity, the longer the time between pulses( pulse period)

33
Q

Why when we look at the sky do the stars seem concentrated to one strip?

A

Because we are seeing one of the strips of the milky galaxy.

34
Q

Nebulae

A

Objects that looked spiral-shaped but some faint, fuzzy objects

35
Q

What was Shapley’s argument?

A

Shapley believe the universe was just one gigantic galaxy 100000 parsecs across.

He reckoned our sun and solar system were far from the centre of the galaxy.

He believed that nebulae were huge clouds of gas and dust. These clouds were relatively nearby and actually part of the Milky Way.

36
Q

What was Curtis’argument?

A

Curtis thought the Universe was made up of many galaxies.

He thought our galaxy was smaller that Shapley suggested- about 10000 pc across, with the sun near the centre.

The spiral nebulae were other very distant galaxies, completely separate from the Milky Way.

37
Q

What points were right from Shapley’s and Curtiss argument?

A

Shapley was right that the solar system is far from the centre if our galaxy, but Curtis was right that there are many galaxies in the Universe.

38
Q

How did Hubble help solve Curtis-Shapley debate?

A

Using a large telescope he found this spiral-shaped nebulae contained many stars, some which were Cepheid variables.

Using this he calculated they were all to far away to e part of the Milky Way galaxy so they met be separate galaxies.

39
Q

Red shift

A

When a galaxy is moving away the light becomes redder.

40
Q

How did Hubble suggest the whole universe is expanding form a single point.

A

Using red shift, Hubble compared the speed and the distances for many galaxies and found a pattern: The more distant the galaxy,the faster it moves away from us.

This suggests that the whole universe is expanding from a single point-which would explain by an initial explosion millions of years ago that started off the expansion.

41
Q

What does kinetic theory says?

A

That gases consist of very small particles that are constantly moving in completely random directions.

They constantly collide with each other and the walls of their container.

42
Q

For both kelvin and Celsius give their temperatures at absolute zero, freezing point of water and boiling point.

A

Absolute zero- It is -273 Celsius and 0 kelvin.

Freezing point of water- It is 0 Celsius and 273 Kelvin.

Boiling point of water- 100 Celsius and 373 kelvin.

43
Q

Outward pressure=

A

When particles collide they exert a force, in a sealed container, gas particles smash against the containers wall- Creating an outward pressure.

44
Q

Explain how pressure increases when you half the volume of container.

A

When you half the volume of a container the particles are more squashed up so they hit the walls more often, hence pressure increases.

45
Q

Nuclear fusion=

A

Two nuclei combining(fusing) to create a larger nucleus.

46
Q

What is needed for fusion to occur?

A

The nuclei must be brought very close together.

For that you need high pressures and temperatures.

47
Q

Give the fusion equation.

A

E= mc2

Energy= mass x speed of light in a vacuum squared.

48
Q

Ionisation=

A

When electrons can gain enough energy to be removed form the atom.

49
Q

What is absorption spectra?

A

At high temperatures, electrons become excited and jump to higher energy levels by absorbing radiation, because there are only certain energy levels an electron can occupy, electrons absorbs particular frequency of radiation to get a higher energy level.

You can see this if a continuous spectrum of visible light shines through a gas- the electrons in the gas absorb certain frequencies of the light, making gaps in a continuous spectrum, they appear as dark lines.

50
Q

What’s a emission spectra?

A

Electrons are unstable in the higher energy levels so they tend to fall from higher to lower levels, loosing energy by emitting radiation of a particular frequency. This gives a series of bright lines formed by emitting frequencies.

51
Q

How do astronomers use spectra to work out what stars are made of?

A

The photosphere of a star emits a continuous spectrum of radiation. This radiation passes through the gases in a star’s atmosphere, which produces emission and absorption lines in the spectrum.

By looking at the spectrum you can work out what chemical elements are present in the stars atmosphere by comparing its known spectra in the lab.

52
Q

What happens to a flames light as it gets hotter.

A

Expands from red light( inferred) to different visible light which become white light ( all light) to ultraviolet.

53
Q

Why is the light emitted from stars helpful?

A

Looking at the colour from stars we can tell what elements are in them and how hot it is.

54
Q

What will be the differences between a blue star( very hot) and a red star( cool star) on a graph?

A

The blue star will have a higher peak than the red star.

55
Q

Hubbles constant=

A

72

56
Q

Explain all the sequences of how cloud of dust and gas become a main sequence star.

A

1) Start of as cloud and dust( mostly helium and nitrogen)
2) The denser bits clump due to gravity
3) when the clumps get dense enough, the cloud breaks up into protostars.
4) Protostars continue to collapse under gravity- reducing in volume. This increases the pressure and temperature.
5) Eventually the temperature of the star reaches a few million degrees, and hydrogen nuclei start to fuse together to form helium.
6) This releases lots of energy creating an outward pressure to stop gravitational collapse.
7) The star has now reached the MAIN SEQUENCE stage. It stays the same, while hydrogen fuses into helium in the core.

57
Q

Describe the core of a star.

A
  • most of the fusion takes place in the core, because the pressure from the weight of the rest of the star makes the core hotter and denser than the rest of the star, so more nuclei fuse together.
58
Q

Describe the photosphere of a star.

A
  • Where energy is radiated into space.
  • part of sun we see from Earth
  • Energy released from fusion in the core is transported by photons of radiation and convection currents to the surface of the star.
59
Q

What happens when a star runs out of hydrogen in the core?

A

1) A star stops being in the main sequence when it runs out of hydrogen in the core.
2) It then swells up to become a red giant or supergiant star.
3) In the process of swelling up, the star’s photosphere cools down.

60
Q

What can a more massive star do?

A

A massive star can fuse heavier nuclei together, and become hotter than a normal star because it puts more pressure on the core.

61
Q

How can a main sequence star become a white dwarf?( a fucking big question, prepare you’re buthole)

A

1) a star runs out of hydrogen to fuse, the core shrinks and the rest of the star expands and it’s photosphere cools.
2) Low mass stars like our sun become red giants.
3) The core is compressed by surrounding matter of the star and shrinks. Till the pressure of the core is high enough for helium fusion to begin. The star releases energy by fusing helium into larger nuclei like carbon, nitrogen and oxygen.
4) when helium runs out and fusion ends, the core is compressed by the rest of the star.
5) a red giant doesn’t have enough mass to compress the core, so no more nuclear fusion occurs.
6) the other layers of the star are thrown off into space and the core shrinks to become a hot white dwarf.
7) In a white dwarf, no nuclear fusion occurs so the star gradually cools and fades.

62
Q

Explain how a main sequence star becomes a neutron star or black hole.

A

1) a star runs out of hydrogen to fuse, the core shrinks and the rest of the star expands and it’s photosphere cools.
2) High mass stars become red supergiants.
3) Red supergiants have enough mass to increase the pressure( and temp) of the core to fuse larger nuclei.
4) Each time an element in the core becomes depleted, the core shrinks until it is hot enough for fusion to occur. This happens till most of the core has been fused into iron.
5) red supergiants cannot fuse iron, so the core collapses and the star explodes as a supernova- creating nuclei with masses greater than iron
6) The core collapses to form a neutron star, or if there’s enough matter, a black hole.

63
Q

Describe the order in which the temperature of the stars go in from high to low.( white dwarfs, main sequence and red giants and supergiants)

A

1) White dwarfs
2) Main sequence
3) Red giants/ Red supergiants

64
Q

What are the advantages of having a computer controlled telescope?

A

1) program telescope to track object in the sky
2) can be programmed to scan across large areas of the sky.
3) allows telescopes to be positioned more precisely
4) can control telescopes via Internet/ work form their office
5) computer control allows many telescopes to point in the same position int he sky.
6) Astronomers only observe at night so they use telescopes from different parts of the world
7) computers can also record and process data from telescopes
8) computer control allows us to control space telescopes.

65
Q

How does the atmosphere make it hard to observe space?

A

1) atmosphere lets certain wave lengths of electromagnetic radiation through and blocks all the others.
2) radio waves can pass through atmosphere well while visible light can be affected badly.
3) Light gets refracted by water int he atmosphere which blurs the images.
4) light can also be absorbed by dust particle in the air.

66
Q

Why are astronomical sites picked carefully?

A

To minimise all the problems caused by atmosphere, another solution is to take measurements above the atmosphere.

67
Q

What is sending space telescopes not that supported?

A

1) Things can go wrong and people have to go up into space to fix it.
2) earth based telescopes are much cheaper and easier to build and maintain.
3) Astronomers have developed good techniques to remove
effects of the atmosphere from their measurements so the images are clearer.
4) less demand on Earth telescopes as there are more.
5) they are really expensive
6) government has to balance this with other priorities like healthcare.
7) the funding for space programmes is never guaranteed.
8)

68
Q

Why so it better when countries work together?

A

By working together, you can get the best people and best facilities for the job.
- countries share costs and resources.

69
Q

What is the international space station?

A

A project led by the US with help of 15 other countries including European Space Agency. Each country is providing different parts of the station.

70
Q

What is the European Extremely Large Telescope?

A

Project involving astronomers across the whole of Europe, but based in Chile. It’s to complex and expensive for a single country to build and operate.

71
Q

What are some factors needed when choosing a Observatory?

A

1) Optical observatories are often put in remote locations, this is to avoid manmade light pollution.
2) away from dust and other particles.
3) astronomers want as little atmosphere between the observatory and telescope as possible to minimise distorting and blurring effects it has, so some are built on high elevation.
4) water in the atmosphere can cause problems by refracting light, so a dry location with low atmospheric pollution is good for a telescope.
5) clouds block a telescope’s view of the sky, so they’re built I’m places with cloudless nights.

72
Q

When making a telescope what are some other factors that need to be taken into account?

A

COST- The cost of building, running and closing down of to need to be considered.
ACCESS- Site will need roads built to it as well as electricity and other facilities.
ENVIRONMENT- Scientist have to be careful and not damage the surrounding environment as little as possible.
SOCIAL- People will be working there, they’ll need water,electricity,accommodation and shops etc. This will be expensive to provide.
- will bring jobs to the area.

73
Q

Look at the temperatures and write down the value in K and Celsius.

  • absolute zero
  • freezing point of water
  • boiling point of water
  • human body temperature
A
  • 0K and -273 C
  • 273K and 0C
  • 373K and 100 C
  • 310K and 37 C

Science (5 decks)

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