P8.3

Question 1

what is the doppler effect?

Answer 1

physical phenomena by which there is a change in the observed frequency/wavelength of a wave (due to relative motion between observer and source

Question 2

what is red shift?

and what does it imply

Answer 2

the shift in wavelength of the lights from distant stars/galaxies to longer wavelengths

• implies stars moving away from us

Question 3

what is blue shift?

and what does it imply

Answer 3

the shift in wavelength of the lights from distant stars/galaxies to shorter wavelengths

• implies stars moving towards us

Question 4

how is red shift linked to the big-bang model?

Answer 4

• light from distant galaxies is red shifted
  so galaxies are moving away from us
• and so if all galaxies are moving away from each other, at one point all matter must have existed at a single point in space

Question 5

how does the distance of a galaxy affect the red-shift?

Answer 5

further away = greater red-shift

means it is moving away faster

Question 6

what is a spectrum?

Answer 6

the range of wavelengths/colours observed when light from a source is separated into separate wavelengths

Question 7

how do we know if light is red shifted?

Answer 7

the black lines (which correspond to specific wavelengths of light absorbed by certain atoms in the star)

• have been shifted towards longer wavelengths

Question 8

what is the second piece of evidence for the big bang theory?

Answer 8

cosmic background radiation

CMBR

Question 9

what is strange about cosmic background radiation?

Answer 9

it fills the universe almost uniformly

Question 10

describe how CMBR gives evidence for the big bang theory

Answer 10

• at beginning of universe, all energy manifested as short gamma rays
• universe expanded = radiation stretched out to longer wavelengths
• ie. microwave radiation
• suggests all started off at single point (as evenly fill the universe)

Question 11

what is the steady state theory?

Answer 11

idea that all of the universe appeared at the same time

Question 12

do scientists think that the galaxies themselves are moving?

Answer 12

no, but the space between them is somehow expanding

Question 13

how was CMBR discovered?

Answer 13

in 1960, two scientists placed sensors.

detected microwave radiation coming from all directions

Question 14

how was our sun formed?

Answer 14

dust and gas drawn together by gravity

Question 15

what allows fusion reactions to occur in stars?

Answer 15

• gravitational attraction between dust particles draws them closer
• so temp + pressure increases
• so particles can fuse together

Question 16

how does an equilibrium form within a star?

Answer 16

energy released during fusion opposes the gravitational collapse due to gravity

Question 17

what are the 8 planets of the solar system (and order)

• give mnemonic to remember it

Answer 17

my very easy method just speeds up naming (planets)

```
mercury
venus
earth
mars
jupiter
saturn
uranus
neptune
pluto
~~~

Question 18

what 5 things make up the solar system, and describe briefly what they are

Answer 18

sun
star at the centre of the solar system

planets
spherical bodies that orbit the sun

moons
spherical bodies that orbit planets

minor planets
small spherical objects that orbit the sun

comets
dust/ice that orbit the sun with long (elliptical) orbits

Question 19

what are the inner planets?

Answer 19

mercury, venus, earth, mars

Question 20

what are the outer planets?

Answer 20

jupiter, saturn, uranus, neptune

Question 21

major difference between inner and outer planets?

Answer 21

inner = rocky, have an atmosphere

outer = gas giants (rings and lots of moons)

Question 22

how was the asteroid belt formed?

and where is it

Answer 22

pieces of rock left over from the formation of the solar system (between jupiter and mars)

Question 23

how was the solar system formed?

Answer 23

• sun + rest of solar system formed from remains of a supernova
• clouds of dust + gas pulled together by gravity
• enough gas + dust gathered = nuclear fusion stars
• protostar formed

Question 24

how does a protostar become a main sequence star?

Answer 24

• becomes denser and hotter
• particles speed up
• particles collide more energetically
• nuclear fusion begins

Question 25

describe the life cycle of a star

Answer 25

• dust + gas gather under gravity = protostar
• once protostar = hot + dense enough, nuclear fusion begins = main sequence star
• star is stable in main sequence EQUILIBRIUM
  ie. radiation pressure outwards (fusion) = gravitational attraction inwards
• radiation pressure drops (no more hydrogen nuclei to fuse)
• gravitational force collapses star
• fusion of heavier elements begin
• star expands (either red giant, or red super giant)

Question 26

why do stars expand when the fusion of heavier elements begin?

Answer 26

• energy of fusion increases
• radiation pressure increases
  (greater than gravitational attraction)

Question 27

what is the last stage of the life cycle of a small star?

Answer 27

• fusion slows down
• radiation pressure decreases
• gravitational force collapses star
• heats up = white dwarf
• eventually cools = black dwarf

Question 28

what is the last stage of the life cycle of a large Star?

Answer 28

• lots of heavier nuclei fuse to release LOTS of energy
• large increase in radiation pressure outwards
• larger than gravitational pull inwards
• star explodes to supernova
• dense neutron star forms

(if very dense = black hole)

Question 29

simple description of life cycle of low mass star?

Answer 29

protostar
               ↓
main sequence star
               ↓
         red giant
               ↓
       white dwarf
               ↓
       black dwarf

Question 30

simple description of life cycle of high mass star?

Answer 30

protostar
               ↓
 main sequence star
               ↓
     red super-giant
               ↓
        supernova
               ↓
      neutron star
               ↓
     (if high mass) 
      black hole

Question 31

compare inner and outer planets

Answer 31

inner - mostly rocky
outer - mostly gas

inner - small mass, small gravitational fields, few moons

outer - large mass, large gravitational fields, many moons

Question 32

why is the sun not expanding?

Answer 32

balance between force of gravity inwards and radiation pressure from nuclear fusion outwards

Question 33

why do larger planets tend to have rings and more moons

Answer 33

• larger mass = larger gravitational pull

attracts debris/plents

Question 34

what does the intensity and the wavelength of emitted radiation depend on?

Answer 34

temperature of the body