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Physics A Level COPY > Chapter 20 Cosmology (The big bang) > Flashcards

Chapter 20 Cosmology (The big bang) Flashcards

1
Q

What is an astronomical unit? What is its distance?

A

It is the average distance between the earth and the sun.

It is 1.5x10^11m

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2
Q

What is a light year? How far is it?

A

It is the distance that light travels in a vacuum in a time of 1 year
9.46x10^15m

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3
Q

What is an arcminute? How many arcminutes are there in 1º?

A

An arcminute is a way of splitting up 1º into smaller parts which is usefull when measuring long distances. There are 60 arcminutes in 1º

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4
Q

How many arcseconds are there in 1 arcminute?

A

60

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5
Q

How many arcseconds are there in 1º?

A

3600

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6
Q

How is a parsec defined?

A

It is defined as the distance at which a radius of 1 AU subtends an angle of one arcsecond.
or in simpler terms
It is the distance produced from the sun to a point when the angle between the point and the sun and the point and the earth is 1 arcsecond

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7
Q

What is the distance of a parsec in metres?

A

3.1x10^16m

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8
Q

What will the angle between the earth and a point and the sun and a point if the point is 3 parsecs away?

A

It will be 1/3 arcseconds

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9
Q

What is stellar parallax?

A

It is a technique used to determine the distance to stars that are relatively close to the earth. Less than 100pc distance

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10
Q

What is parallax?

A

It is the apparent shift in the position of a relatively close star against the backdrop of much more distant stars as the earth orbits the sun

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11
Q

How does stellar parallax work?

A

A close star is viewed from earth against the background of other stars.
Then 6 months later as the earth is on the opposite side of the sun, the star is then viewed again against the background of other stars.
If the parallax angle (the angle between the star and the sun and the star and the earth) is calculated in arcsecondsthen this can be used to work out the distance of the star from the sun.

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12
Q

What is the equation for stellar parallax?

A 
d = 1 / p
d = distance
p = parallax angle in arcseconds
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13
Q

Why is stellar parallax limited to close stars?

A

As the star gets further away the parallax angle is harder to calculate accurately so an inaccurate distance would be calculated

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14
Q

What is doppler shift?

A

As a wave source moves relative to an outside observer, the frequency and wavelength of the waves received by the observer change based off the speed of the moving wave source

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15
Q

Explain doppler shift using a F1 car as an example?

A

As an F1 car moves towards a stationary observer, the sound waves get bunched up in front of the car producing a higher pitched sound.
As an F1 car moves away from a stationary observer the sound waves get spread out behind the car and produces a lower pitched sound.
This is why F1 cars make the “Neeeee-awwwwwwwww” sound

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16
Q

What sort of waves does the doppler shift apply to?

A

It applies to all types of waves

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17
Q

How can the doppler shift be used?

A

It can be used to work out the speed of moving objects

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18
Q

What is blue / red shift and where does it occur?

A

As galaxies move towards or away from the earth the light that they produce will be doppler shifted.
If a galaxy is moving towards the earth the light will be shifted towards the blue end of the spectrum (aka blue shifted)
If a galaxy is moving away from the earth then the light will be shifted towards the red end of the spectrum (aka red shifted)

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19
Q

What is the doppler equation?

A

Δλ / λ = Δf / f = v / c

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20
Q

The faster a wave source moves…

A

The greater the doppler shift

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21
Q

What did Hubble observe?

A
  • The majority of galaxies were red-shifted and were moving away
  • The galaxies that were furthest away were more redshifted and so were moving faster
22
Q

What did Hubble do with these observations?

A

He formulated Hubbles law from his observation which said that the speed of the galaxy is directly proportional to the distance. He gathered data from lots of galaxies and plotted them on a graph and used a line of best fit through the origin

23
Q

What is the equation for Hubbles law?

A 
v = H0d
v = velocity
H0 = Hubbles constant
d = distance from the earth
24
Q

What are the units for Hubbles constant?

A

s^-1

25
Q

What is the value of Hubbles constant?

A

2.2x10^-18s^-1

26
Q

Do all galaxies follow Hubbles law?

A

No, It is simply a model for how most galaxies move

27
Q

What sort of speed must a galaxy be moving for the Doppler equation to work?

A

Far less than the speed of light

28
Q

What did Hubbles law say about the model of the universe?

A

It says that the universe is expanding and has been expanding since the big bang. Galaxies aren’t just moving apart but space and time itself is expanding

29
Q

What is the cosmological principle?

A

This is the assumption that the universe is Homogeneous, isotropic and the laws of physics are universal

30
Q

What does homogeneous mean when it comes to the cosmological principle?

A

Matter is distributed uniformly when considering a VARY large volume

31
Q

What does isotropic mean when it comes to the cosmological principle?

A

It looks the same in all directions, there is no centre or edge

32
Q

What does it mean when the laws of physics are universal when talking about the cosmological principle?

A

The laws of physics are the same everywhere and can be applied across the universe

33
Q

What are the two big theories that support the big bang theory?

A

Hubble’s law and microwave background radiation

34
Q

How does Hubble’s law provide evidence for the big bang theory?

A

It says that the universe is expanding and so at some point it must have been much smaller and eventually, a long time ago, it was all contained in one hot dense point.

35
Q

How was microwave background radiation produced? (2 ways)

A
  • At the beginning of the universe it was very hot and dense and saturated with high energy gamma photons and as the universe has expanded the wavelength of the gamma photons has expanded and now are microwave photons
  • The universe can act as a black body radiator and at its current temperature of 2.7K the peak wavelength of EM radiation is about 1mm which is the same region as microwave
36
Q

How does microwave background radiation provide evidence for the big bang theory?

A

None of the other universe creation theories could explain microwave background radiation

37
Q

How can we calculate the age of the universe? What is the assumption?

A

Age = 1 / H0

Assuming that the universe has been expanding at the same rate

38
Q

Has the universe been expanding at a constant rate?

A

No, current evidence says that it is accelerating

39
Q

What is an estimation for the age of the universe?

A

4.5x10^17s ≈≈ 14 Billion years

40
Q

What is dark energy?

A

This is a hypothetical form of energy that fills all of space and contributes to the acceleration of the universe

41
Q

What happened during the instant of the big bang?

A

Time and space is created

The universe is a singularity, infinitely dense and hot

42
Q

What happened after 10^-35s of the universe being created?

A

The universe rapidly expands, this is called inflation
There is no matter in the universe only high energy gamma photons
The temperature is very high, 10^28K

43
Q

What happened after 10^-6s of the universe being created?

A

The first fundamental particles are created (quarks and leptons)
The universe gains mass

44
Q

What happened after 10^-3s of the universe being created?

A

Quarks combine to form the first hadrons such as protons and neutrons
Most of the mass was created through pair production (high energy photons turning into a particle and an antiparticle)

45
Q

What happened after 1s of the universe being created?

A

The creation of matter stops

The temperature is about 10^9 K

46
Q

What happened after 100s of the universe being created?

A

Protons and neutrons fuse together to make essential nuclei
The rate of expansion is much slower
25% of the universes mass is in helium nuclei (known as primordial helium)

47
Q

What happened after 380,000 years of the universe being created?

A

The universe cools enough for nuclei to attract electrons and form atoms. The EM radiation produced at this stage is what is now microwave background radiation

48
Q

What happened after 30 million years of the universe being created?

A

The first stars appear and start to form the heavier elements

49
Q

What happened after 200 million years of the universe being created?

A

The milky way forms

50
Q

What happened after 9 Billion years of the universe being created?

A

The solar system is formed from the nebula left by a supernova
1 Billion years later the earth forms and 1 billion years after that, lift starts to form

51
Q

How was dark matter discovered / theorised?

A

It is expected that stars on the edge of the galaxy would travel slower than the galaxies in the middle where the mass is concentrated.
This is not the case, stars on the outside travel fastest and therefore the mass must be concentrated at the outside of the galaxy. This mass that cannot be seen is dark matter

52
Q

What is dark matter?

A

No one knows

Physics A Level COPY (27 decks)

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