Markscheme for questions on Cosmology

1.       any 4 from:
end of H burning/red giant/supergiant (1)
onset of He fusion/fusion of heavier nuclei (1)
gravitational collapse of core (1)
supernova explosion/ star explodes (1)
suitable mass limit (chanderasekha limit 1.4M) (1)
supported against gavity by neutron gas pressure/ ref to
Fermi pressure (1)
internal structure protons and electrons combined/ very
thin atmosphere/ metallic crust (1)                                                                             4

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  2.     Any 5 from
red shift data for galaxies (accept stars)                                                                     1
calculate velocity from red shift                                                                                1
galaxies/ stars receding from Earth                                                                             1
distance data for galaxies/ stars                                                                                  1
velocity α distance / v/r = constant / v-r graph straight line                                         1
universe began at a single point                                                                                 1

[5]

  3.     (a)     Any two
stars rotate around galactic centre                                                                     1
star with velocity component towards Earth                                                     1
reference to motion/shape of galaxy                                                                1
or other valid points eg blue shift

  (b)   Ho = 75/ 3 × 1019 s–1                                                                                        1
t ≈ 1/ 2.5 × 10–18                                                                                              1
t ≈ 4 × 1017 s                                                                                                    1

[5]

  4.     Hydrogen atoms/particles (1)
Collapse under gravity/ decrease of gpe (1)
Increase in kinetic energy/ temperature (1)
Fusion of protons (1)
Energy released/ ref. to E = ∆mc2 (1)

[5]

5.       Any 6 from
Nuclear/hydrogen burning ends (1)

          Mass > Chandrasekhar limit (1)

          Expanding gas/planetary nebular/red giant (1)

          Gravitational collapse /ref. to burning He or higher metals (1)

          Correct ref. to (Fermi) pressure/ radiation pressure (1)
(must have ref. to pressure or force from radiation.)

          Neutron star (neutron by itself, not enough) (1)

          Correct reference to Schwarzschild radius/
allow mass> 3M/ allow ref. critical radius (1)

          Black Hole (1)                                                                                                           6

[6]

  6.     Ho2 = (1 × 10–26 × 8 × π × 6.67 × 10–11) / 3                                                             C1
Ho = 2.36 × 10–18 s–1                                                                                              A1

[2]

  7.     (i)      v/c = ∆λ / λ (1)
∆λ = 656.3 × 10–9 × 6.1 / 3 × 108 (ignore minus sign) (1)
∆λ = 1.33 × 10–14 m (1)                                                                                    3

  (ii)   Graph: any 4 points plotted correctly (1)
all correct (1)                                                                                                    2

  (iii)  graph: draw curve, reasonable attempt (1)                                                        1

(iv)    Either point where star moves perpendicular to line of sight (1)                       1

  (v)   time = 72 h ± (1)h (ecf read value from their graph ± 1 h) (1)                          1

  (vi)  r = 3√(6.7 × 10–11 × 4 × 1030 × [72 × 3600]2/ 4π2) ecf (1)
r = 7.70 × 109 m ecf . (1)                                                                                  2
(use of t = 72h 1/2)

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