any two from universe expands to a limit flat universe 1 but never reaches that

# Any two from universe expands to a limit flat

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any two from universe expands to a limit/ flat universe (1) but never reaches that limit (1) density of universe = critical density (1) 2 (iii) curve: passes through P (1) curves over and back to time axis (1) 2 (iv) Universe not so old (no ecf from (iii)/ Universe will end in big crunch (no ecf from iii) / universe has finite lifetime (1) 1 [8] 16. (a) uniform intensity detected in all directions/ isotropic 1 (b) Hydrogen and helium in early stars and sun 1 Sun has greater proportion of helium than early stars/ H changed to He by fusion in sun. 1 Virtually no higher elements in first stars/ sun contains traces of higher elements (accept specific examples up to iron) 1 [4] PhysicsAndMathsTutor.com 4
17. 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] 18. critical density is that for flat universe 1 density > p 0 universe closed/contracts/big crunch 1 density < p 0 universe open/ expands forever 1 any 2 from fate unknown because size/mass/density universe uncertain 1 fate unknown because p 0 / H 0 not known 1 [5] 19. Planets move in ellipses (Sun at one focus) (1) Planet sweeps out equal areas in equal times. (1) Period 2 α radius 3 / T 2 / r 3 = constant (1) 3 [3] 20. (i) v/c = ∆λ / λ (1) ∆λ = 656.3 × 10 –9 × 6.1 / 3 × 10 8 (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 × 10 30 × [72 × 3600] 2 / 4 π 2 ) ecf (1) r = 7.70 × 10 9 m ecf . (1) 2 (use of t = 72h 1/2) [10] PhysicsAndMathsTutor.com 5
21. correct reference to (1) AU (1) parallax of (1) arcsecond (marks can be gained on labelled diagram) (1) 2 [2] 22. Any 6 from Nuclear/hydrogen burning ends (1)

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• Spring '18
• fatima
• Big Bang, Cosmic microwave background radiation, Ambrose College

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