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Physics - IGCSE > Ch - 25 (Stars and the Universe) > Flashcards

Ch - 25 (Stars and the Universe) Flashcards

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1
Q

What role does the sun play in the solar system?

A
  • medium sized star
  • hydrogen and helium
  • radiates infrared, UV, and visible light
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2
Q

How are stars classified?

A
  • Colors
  • depends on how hot they are
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3
Q

What is a star’s colour related to?

A

Surface temperature.

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4
Q

What’s the range of star colors from hottest to coldest?

A
  • Blue start is hottest (30 000 K)
  • Red star is coolest (3000 K)
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5
Q

What happens at the center of a stable star?

A

Hydrogen nuclei undergo nuclear fusion to form helium

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6
Q

What happens during nuclear fusion?

A
  • huge amount of energy is released.
  • provides pressure for star that prevents it from collapsing under it’s gravity.
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7
Q

What are galaxies made up of?

A

Made up of billions of stars.

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8
Q

What is the universe made up of?

A

made up of many different galaxies

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9
Q

What is astronomical distance?

A

-distance between stars and galaxies

  • very large
  • light years
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10
Q

Define one light year.

A

The distance travelled by light through (the vacuum of) space in one year.

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11
Q

What is the speed of light known as?

A

Universal speed limit

  • tracked slowly as compared to astronomical distances .
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12
Q

What is the diameter of the milky way?

A

100 000 light years

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13
Q

What is one light year equal to?

A

9.5 x 10 ^12 Km
9.5 x 10^15 m

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14
Q

What are the main stages of star formation?

A
  1. Nebula
  2. Protostar
  3. Main sequence star
  4. low mass star
  5. High mass star
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15
Q

What happens in the stage of nebula in star formation?

A

Form a giant interstellar cloud of hydrogen gas and dust called a nebula.

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16
Q

What happens in the stage of protostar in star formation?

A
  • Force of gravity pulls nebula closer together forming a hot ball of gas known as protostar
  • particles pulled closer, density of protostar increases

-frequent collisions causing temp to increase

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17
Q

What happens in the stage of main sequence star in star formation?

A
  • when protostar is hot, nuclear fusion happens.
  • hydrogen nuclei fuse together to form helium nuclei
  • fusion reaction releases heat (and light)
  • star is in equilibrium, and is stable
  • inward force due to gravity is equal to outward pressure force from fusion reaction
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18
Q

What are the stages in low mass life cycle of a star?

A
  1. Red giant
  2. Planetary nebula
  3. White dwarf
  4. Black dwarf
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19
Q

What happens in the stage of red giant in star formation?

A
  • fusion reaction in star runs out
  • core starts to die down
  • core shrinks (inward force of gravity will become greater than the outward force) and heats up
  • helium undergo fusion to form beryllium
  • cause outer part of star to expand
  • 8 times the mass of the sun
  • outer surface cools and turns red
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20
Q

What happens in the stage of main planetary nebula in star formation?

A
  • star becomes unstable
  • eject outer layer of dust and gas which is called planetary nebula
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21
Q

What happens in the stage of white dwarf in star formation?

A
  • core collapses completely due to pull of gravity
  • White dwarf cools
  • amount of energy it emits decreases
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22
Q

What happens in the stage of Black dwarf in star formation?

A
  • lost significant amount of energy
  • cools until it eventually disappears
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23
Q

What are the stages in High mass life cycle of a star?

A
  1. Red super giant
  2. Supernova
  3. Neutron star (or Black hole)
24
Q

What happens in the stage of red super giant in star formation?

A
  • hydrogen causing fusion reaction runs out
  • High mass star more than 8 times the mass of sun
  • core starts to die down
  • shrinks and heats up
  • expands and constricts
  • fusion reaction will form elements up to iron
25
Q

What happens in the stage of supernova in star formation?

A
  • core collapses suddenly
  • causes gigantic explosion
  • centre of explosion is dense body , called neutron star forms
  • outer remnants of star are ejected into space forming new clouds of dust and gas (nebula)
  • nebula from new stars may form new stars with orbiting planets
26
Q

What happens in the stage of neutron star or Black hole in star formation?

A
  • biggest star
  • center continue to collapse under force of gravity
  • very dense and no light escapes
27
Q

What happens when an object emits waves?

A

Wavefront spread out symmetrically.

28
Q

What 2 factors will a moving object cause a change to?

A

Wavelength and frequency.

29
Q

What happens to wavelength and frequency in a moving object?

A
  • wavelength of the waves in front decreases, and frequency increases
  • wavelength behind the source increases and frequency decreases
  • doppler effect
30
Q

What does the Doppler effect also affect?

A
  • light
  • object moves away then wavelength of light decreases
  • this is red shift as light moves to end of spectrum
31
Q

Define redshift.

A

An increase in the observed wavelength the electromagnet radiation emitted from receding stars and galaxies.

32
Q

How does the light from distant galaxies appear?

A

Redshift

33
Q

How are the lines on the spectrum and what does it indicate?

A
  • shifting towards red
  • galaxies are moving away
  • universe is expanding
  • supports Big Bang Theory
34
Q

What is another observation we can conclude from the light spectrum produced from different galaxies?

A
  • Greater the distance to the galaxy, greater the redshift
  • the further away the galaxy is, the faster it is moving away from us
35
Q

How and when did the Big Bang Theory begin?

A
  • 14 billion yrs ago universe bagan from a very small region that was extremely hot and dense
  • giant explosion
  • universe expanded away from every point
36
Q

What is an evidence for the universe expanding?

A

redshift of distant galaxies

37
Q

What happens when balloon is deflated and expanded? And why?

A
  1. Expands - all points become further apart by same amount
  2. Deflated - all points are close together and equal distance apart

Space itself has expanded between galaxies

38
Q

What are the main pieces of evidence for the Big Bang Theory?

A
  1. Galactic red shift
  2. Cosmic Microwave Background Radiation (CMBR)
39
Q

What does it prove when light spectrum produced from distant galaxies are red shifted more than nearby galaxies?

A
  • Greater the distance to the galaxies, greater the red shift
  • further away galaxy, faster it is moving
40
Q

What is CMB Radiation?

A
  • Type of electromagnetic radiation which is remnant from early stages of the Universe
  • wavelength of 1mm
41
Q

What did astronomers discover in 1964?

A

Microwave from all directions at uniform temperature of 2.73K

Unable to do earlier as microwaves were absorbed

42
Q

How was the early Universe according to Big Bang Theory?

A

extremely hot and dense

Emits thermal radiation

43
Q

How is the thermal radiation of microwave in Big Bang Theory?

A
  • Initially it would be High energy
  • wavelength of radiation increased
44
Q

How is CMB radiation?

A
  • Uniform
  • exact profile to be expected from a hot body
45
Q

What do different colors on CMB radiation mean?

A
  • The red/orange/brown regions represent warmer temperature indicating High density regions
  • Blue regions represent cooler temperatures indication lower desnity
46
Q

what is the formula for measuring the universe and velocity of distant objects from redshifts?

A

difference between actual wavelength and expected wavelength / actual wavelength = speed of galaxy / speed of light

47
Q

How do we measure distance in space?

A

Standard candles including supernovae

48
Q

What are supernovae?

A

Exploding stars

49
Q

how do we measure distance using supernovae?

A
  • some types have have same peak level of brightness (absolute magnitude)

Type 1a supernovae are very brught

50
Q

what happens in 1929 with astronemer Edwin Hubble?

A
  • showed universe is expanding
  • observed the abdsorption of light spectra
  • light was shifted towards the red end of the spectrum
  • observed more distant galaxies are more red shifted than the light
51
Q

What does Hubble’s law state?

A

The recessional velocity v of a galaxy is proportional to its distance from the Earth.

52
Q

How can Hubble’s law be expressed as symbol?

A

H0 = v /d

H0 = Hubble constant (per sec)

v = recessional velocity of an object moving away from an observer (km/s)

d = distance between object and earth

53
Q

Define Hubble constant.

A

The ratio of the speed at which the galaxy is moving away from the earth, to its distance from the earth

54
Q

What is the value of Hubble constant?

A

2.2 x 10^-8 per sec

55
Q

How can the Hubble law equation be rearranged ?ro calculate

A

1 / H0 = d /v

Physics - IGCSE (24 decks)

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