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AstrophysicsM - 1(a S iz e o f U n iv e rs e O pen F la t C...

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1. (a) S i z e o f U n i v e r s e T i m e O p e n F l a t C l o s e d 3 max Award [1] for each correct label. (b) 3 max Type of Universe Relation between ρ and ρ 0 Open ρ < ρ 0 Flat ρ = ρ 0 Closed ρ > ρ 0 Award [1] for each correct entry. [6] 2. (a) the universe is expanding; 1 (b) any sensible straight line; 1 (c) Slope of the graph; 1 (d) T = H –1 ; correct conversion of units to get T 10 10 years; 2 [5] 3. (a) cosmic background radiation is microwave radiation; “filling” the universe / from all directions; 2 Award other relevant and appropriate comments eg “at a temperature of about 3K or left over from the Big Bang”. 1
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(b) the Big Bang predicts an expanding universe that had a very high temperature at the beginning; during the expansion the universe is cooling down and the temperature of the radiation should fall to its present low value, (which is precisely what the cosmic 2 background radiation measures); or Big Bang producing initially very short wavelength photons / em radiation; as the universe expands, the wavelengths become redshifted / longer (to reach current value); 2 (c) the redshift in the light observed from distant galaxies (indicating that they are moving away from each other) / the helium abundance in the universe which is about 25% and is consistent with a hot beginning of the universe;1 Note : question asks for evidence so do not accept “universe is expanding” unless the answer mentions redshift etc. (d) the student is wrong; space is created as the universe expands / there is no outside to the universe; 2 Award [0] if no explanation or incorrect explanation. [7] 4. (a) Diagram should show spiral arms; central disc; the solar system on one of the arms about a third of the way from the centre; 3 Be generous in the position – accept between 4 1 and 4 3 . (b) c v c v = - = 658 658 670 0 λ λ ; hence v = 658 658 670 - c = 0.018 c = 5.47 × 10 3 km s –1 ; 2 Award [1 max] for 670 658 670 - = 0.0179. 2
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(c) (i) straight-line; through origin; 2 ( 0 , 0 ) v d (ii) relative speed of two points in the universe separated by distance d is v = T d where T is the age of the universe / argument to show v = T d ; v = T d = H 0 d therefore T = 0 1 H ; 2 Award [0] for answers that just show that T = 0 H 1 has the right units. (iii) the Hubble constant is obtained from the slope of the graph; 1 [10] 5. (a) if less than ρ 0 , Universe will expand for evermore; if greater than ρ 0 , Universe will expand; and then contract; 3 (b) (i) substitution to give ρ 0 = 1.3 × 10 –26 kg m –3 ; 1 (ii) number density = ) 10 66 . 1 ( ) 10 3 . 1 ( 27 26 - - × × , about 7 or 8 m –3 ; 1 Note : unit is m –3 . [5] 3
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6. (a) (i) N on line between 10 2 s and 10 3 s; 1 (ii) G labelled on line at about 10 13 s; 1 Award 10 12 s to 10 14 s. (b) light takes millions of years to reach Earth; so observations made in the past when universe was warmer; 2 [4] 7. (a) (i) R shown amongst scattered points in upper right of diagram W shown in lower region below main sequence, about centrally; 1 (ii) S shown on main sequence, about 3 1 way up; 1 Allow the position of S anywhere between 4 1 and 2 1 the way up.
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