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GCSE Physics > 8. Astrohphysics > Flashcards

8. Astrohphysics Flashcards

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1
Q

What is a universe

A

Large collection of billions of galaxies

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2
Q

What is a galaxy

A

Large collection of billions of stars

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3
Q

What galaxy is our solar system part of

A

The Milky Way

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4
Q

What does gravitational field strength (g) depend on

A

Mass of the body creating the field

The larger the mass the stronger the gravitational field strength

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5
Q

Why is gravitational field strength different on the earth and moon

A

Earth is more massive than the moon ( large mass)

So an object object would weigh more on earth than it would on the moon

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6
Q

Why is gravitational field strength different on different planets

A

g varies with distance

The closer you get to a star or planet the stronger the gravitational force

Planets closer to the sun orbit it faster because the stronger force requires a larger instantaneous velocity needed to balance it

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7
Q

What does gravitational force cause

A

Orbits

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8
Q

What do moons orbit

A

Planets

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9
Q

What do planets orbit

A

The sun

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10
Q

What orbits the earth

A

Artificial satellites

Eg moons

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11
Q

what do comets orbit

A

the sun ( comets tails face away from the sun)

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12
Q

what the differences in the orbits of comets moons and planets

A

moons and planets= slightly elliptical

comets = highly elliptical

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13
Q

Describe a comets orbit

A

elliptical
longer orbital periods than earth
travel faster when nearer the sun

need to add more

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14
Q

equation for orbital speed

A

(circumference)/ time period

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15
Q

how can stars be classified

A

by colour

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16
Q

what are the colors used to classify stars

A 
Blue 
white 
yellow 
orange 
red
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17
Q

Describe the relationship between a stars color and it temperature

A 
Blue = Hottest
white 
yellow
orange
red = coolest
18
Q

what is the life cycle of a star with a similar mass to the sun

A
  1. nebula
  2. protostar
  3. Main sequence star
  4. red giant star
  5. white dwarf
19
Q

definition of nebula

A

a cloud of dust and gas

which stars initially form from

20
Q

how is a protostar formed

A

force of gravity pulls dust and gas together ( to form a protostar)

21
Q

how is a star formed from a protostar

A
  1. gets denser + more particles collide= temp rises
  2. temp high enough= hydrogen nuclei undergo nuclear fusion = form helium nuclei
  3. nuclear fusion= releases huge amount of energy (thermal expansion)

= keep core of star hot

22
Q

describe a main sequence star

A
  1. long stable period
  2. outward pressure caused by thermal expansion ( energy produced by nuclear fusion) balances force of gravity pulling everything inwards )

( the force of gravity holding the star together is balanced by higher pressure due to the high temperatures.)

23
Q

how long does the stable period main sequence star last

A

several billion years

heavier the star the shorter its time on the main sequence

24
Q

how is red giant formed from a star

A
  1. hydrogen in core used up ( in fusion)
  2. force due to gravity = larger than the pressure of thermal expansion
  3. star compressed by gravity until dense and hot enough = energy created = outer layers of star expand

( larger nuclei begin to form and the star may expand to become a red giant = bigger than the sun.)

  1. star becomes a red giant ( if small star = same size sun)
25
Q

how is a white dwarf formed from a red giant

A
  1. red giant becomes unstable
  2. = ejects outer layer of dust and gas
  3. = hot , dense solid core = white dwarf
26
Q

describe the evolution of red super giant ( stars much bigger than the sun ) to form a supernova

A
  1. start to glow brightly again
  2. undergo more fusion = make heavier elements
  3. expand + contract several times as balance shifts between gravity + thermal expansion
  4. eventually explode in a supernova
27
Q

how is a neutron star formed from a supernova

A
  1. exploding supernova = throws out layers of dust + gas

2. = leaves very dense core = neutron star

28
Q

how is a black whole formed form a neutron star

A
  1. if neutron star massive enough = collapse + become black hole
  2. black hole = super dense point in space that not even light can escape from
29
Q

PAPER 2

how is the brightness of a star at a standard distance represented

A

by using absolute magnitude

30
Q

PAPER 2

definition absolute magnitude

A

measure of how bright a given star would appear to be if it was a fixed distance from Earth

= allows us to compare the brightness of stars

the lower the absolute magnitude = the brighter the star ( very bright stars = -ve absolute magnitude )

31
Q

PAPER 2

definition of the Hertzsprung-Russell Daigram ( HR diagram)

A

is a graph of absolute magnitude against temperature for many, many stars

32
Q

PAPER 2

need to be able to draw a HR diagram for the main components

A

???
Red giant + red supergiant = top right

White dwarf = bottom left

Main Sequence = span whole range of graph diagonally from top-left to bottom-right

33
Q

PAPER 2

describe the past evolution of the universe + main arguments for the big bang

A

???

  1. initially all matter of universe occupied a single point
  2. this tiny space = very dense + very hot
  3. single point the explode = Big Bang
  4. space started expanding and the expansion is stil going on
34
Q

PAPER 2

what evidence is there to support the Big Bang

A 
Red Shift (suggests universe is expanding )
Cosmic microwave background = CMB ( CMB radiation = leftover energy of this initial explosion )
35
Q

PAPER 2

what happens when a wave source is moving relative to an observer

A

there will be a change in the observed frequency and wavelength ( compared to when they were emitted ) = Doppler Effect

happens with all waves incl. light

36
Q

PAPER 2

definition of red shift

A

if a light source is moving away from you = light it emits will appear to be shifted towards the red ( ie. lower frequency end ) of the visible part of the EM spectrum

37
Q

PAPER 2

definition of Cosmic Microwave Background ( CMB ) radiation

A

the low frequency microwave radiation coming from all directions and all parts of the universe ( that scientist can detect )

38
Q

PAPER 2

describe the red shift in light received from galaxies at different distances away from Earth

( why do most galaxies seem to be moving away from each other )

A
  1. different elements absorb different frequencies ( or wavelengths ) of light
  2. when light is passed through a sample of an element = pattern of dark lines is produced
  3. there is dark line at each of the frequencies in the visible part of the EM spectrum that the element absorbs
  4. when we look at light from distant galaxies we see the same patterns but at slightly lower frequencies ( longer wavelengths) than they should be
  5. the patterns = shifted towards the red end of the spectrum = red shift
39
Q

PAPER 2

how does red shift of galaxies provide evidence for the expansion of the universe

A
  1. measurements of red shift suggest all distant galaxies are moving away from us very quickly
  2. more distant galaxies have greater red shifts than nearer ones = show bigger observed decease in frequency ( increased wavelength )
  3. = more distant galaxies are moving away faster that nearer ones
  4. conclusion = whole universe is expanding
40
Q

PAPER 2

what is the equation used for calculations involving red shift

i.e. equation to calculate relative speed between 2 galaxies

A

change in wavelength / ( reference) wavelength = velocity of a galaxy / speed of light

41
Q

PAPER 2

what is the speed if light

A

3 x 10*8 m/s

GCSE Physics (8 decks)

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