Some notes on electro mag can be found here
Monday, May 14, 2012
Wednesday, May 09, 2012
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
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
[4]
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
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
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
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)
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)
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.)
(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)
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
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
∆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
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)
r = 7.70 × 109 m ecf . (1) 2
(use of t = 72h 1/2)
[10]
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