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Physics A-level Paper 2 > Topic 10: Space > Flashcards

Topic 10: Space Flashcards

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1
Q

What properties of a star can we determine from its EM emissions?

A
  • Temperature
  • Chemical Compositiom
  • Size
  • Age
  • Speed
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2
Q

What is luminosity?

A

Luminosity is the rate of light energy released / power output of a star

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3
Q

What is the definition and formula of a star’s intensity?

A

Intensity is the luminosity of a star per unit area. It is inversely proportional to square distance between the star and observer.
I = L/4πd²

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4
Q

What is the definition of parallax?

A

Parallax is the apparent change in position of a nearer star compared to distant stars.

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5
Q

What are the conditions for trigonometric parallax?

A
  • Only works for nearby stars
  • The apparent movement of a nearby star relative to a fixed background
  • by taking measurements 6 months apart when earth is at opposite ends
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6
Q

What is the conversion of Astronomical unit to metres?

A

1 AU = 1.5 x 10¹¹ m

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7
Q

What is the conversion of parsec to light years?

A

1 Parsec (pc) = 2.06 x 10⁵ AU = 3.08 x 10¹⁶ m = 3.26 ly

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8
Q

What is a standard candle?

A

A standard candle is an object of known luminosity.

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9
Q

How do you use standard candle to determine astronomical distances?

A

d² = L/4π x l

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10
Q

What is the stellar evolution for stars <3M☉?

A

For stars of mass <1.4M☉
1. Main sequence star
2. Protostar
3. Red giant
4. White dwarf
5. Black dwarf

For stars of mass 1.4M☉ - 3M☉:
1.Protostar
2. Main sequence star
3. Red giant
4. Supernova
5. Neutron Star or Black Hole

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11
Q

What is the stellar evolution for stars of mass >3M☉?

A

For stars of mass >3M☉:
1. Protostar
2. Main sequence Star
3. Red supergiant
4. Supernova
5. Neutron star or black hole

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12
Q

What are the properties of a protostar?

A
  • Large quantity of mass (mainly hydrogen0 gathering due to gravity attracting it together
  • no fusion taking place
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13
Q

What are the properties of a main sequence star?

A
  • Hydrogen fusion takes place
  • inward gravitational force is equal to the outward pressure from hydrogen fusion reaction. Forces are balanced.
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14
Q

What are the properties of a red giant?

A
  • Towards end of main sequence, hydrogen fusion stops in the core and collapses.
  • Temperature is high enough to fuse helium into heavier elements.
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15
Q

What are the properties of a white dwarf?

A
  • Fusion stops as star can no longer fuse heavier elements together.
  • No outward force due to no fusion so the star collapses under its own gravity and becomes white dwarf
  • Stars temperature increases as it contracts inwards and continues to glow as a white dwarf.
    -Temp not hot enough for heavier elements
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16
Q

What are the properties of a black dwarf?

A

When the star cools down, it settles as a black dwarf.

17
Q

What are the properties of a red supergiant?

A

When a high mass star runs out of nuclei, the same process for red giant occurs but on a larger scale.

18
Q

What are the properties supernova?

A
  • When all fuel runs out, fusion stops and the core collapses inwards and becomes rigid.
  • Outer layers of star fall inwards and rebound off the core launching them out into space in a shockwave.
  • As the shockwave passes through surrounding ,aterial, elements heavier than iron are fused and flung into space
19
Q

What are the properties of a neutron star?

A
  • When the core of a large star collapses, gravity is so strong, it forces protons and electrons together to form neutrons.
20
Q

What are the properties of a black hole?

A

When the core of a giant star collapses, the neutrons are unable to withstand gravity forcing them together.

21
Q

What is the doppler effect?

A

Apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.

As the source is moving, the wavelengths in front of it are compressed and the wavelengths behind are spread out. Similar to sound of car moving past you.

22
Q

What is red-shift?

A

Red shift happens when a star moves away from Earth. EM Wavelength observed on Earth is longer than wavelength initially emitted from source (laboratory wavelength).

23
Q

What is blue-shift?

A

Blue shift is exhibited when a star moves towards observer. Wavelength observed is shorter than the wavelength initially emitted.

24
Q

Describe how distances too large for the use of standard candles can be determined

A
  • Measure change in λ/f
  • Determine relative velocity using redshift equation
  • Use v=H₀d
25
Q

Describe how astronomers would have determined the velocity of each galaxy

A
  • Measure λ of light from the galaxy
  • Compare it to λ for a source on Earth
  • Reference to spectral line; differences in spectral line
  • Difference in λ means doppler effect occurs where λ changes due to galaxy moving away/towards observer
  • v is found from redshift equation
26
Q

2 reasons why scientists are uncertain about ultimate fate of Universe

A

Dark matter
- Existence of dark matter
- Values of average density and mass have large uncertainty and inaccurate
- So measurements of critical density of the Universe has large uncertainty

Difficulty of distance measurements
- Difficulty in making accurate measurements of distances to galaxies
- Hubble’s constant has large uncertainty/inaccurate

27
Q

Explain how redshift can be used to determine velocity of galaxy relative to Earth

A
  • Measure λ/f of light from galaxy
  • Compare measured λ/f to λ/f for a source on earth
  • Use z=v/c to calculate it
28
Q

How does average density determine universe ultimate fate?

A

Greater than critical value
- Universe will contract
Less than critical value
- Universe will continue expanding
Same as critical value
- Universe will not contract or expand

29
Q

How have astronomers deduced that white dwarfs have small surface area?

A

White dwarf have
- High temp as λmax is small
- Low luminosity
L=σAT⁴

30
Q

Characteristics of main sequence star

A
  • Hydrogen fusion takes place; primarily converting hydrogen to helium in their core
  • Stars on main sequence maintain constant luminosity for most of lifetime
31
Q

Why do biggest stars have greatest luminosity?

A
  • Massive stars experience much greater g forces
  • So core temperature and density is greatest
  • Rate of fusion in core is greatest
  • Surface temperature is higher
  • So surface are is greatest

Physics A-level Paper 2 (7 decks)

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