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Date	May 2018	Marks available	3	Reference code	18M.3.SL.TZ2.12
Level	Standard level	Paper	Paper 3	Time zone	2
Command term	Estimate	Question number	12	Adapted from	N/A

Question

Data from distant galaxies are shown on the graph.

M18/4/PHYSI/SP3/ENG/TZ2/12

Estimate, using the data, the age of the universe. Give your answer in seconds.

[3]

a.

Identify the assumption that you made in your answer to (a).

[1]

b.

On the graph, one galaxy is labelled A. Determine the size of the universe, relative to its present size, when light from the galaxy labelled A was emitted.

[3]

c.

Markscheme

use of gradient or any coordinate pair to find H₀ «= $\frac{v}{d}$ » or $\frac{1}{{{H_0}}}$ «= $\frac{d}{v}$ »

convert Mpc to m and km to m «for example $\frac{{82 \times {{10}^3}}}{{{{10}^6} \times 3.26 \times 9.46 \times {{10}^{15}}}}$ »

age of universe «= $\frac{1}{{{H_0}}}$ » = 3.8 × 10¹⁷ «s»

Allow final answers between

3.7 × 10¹⁷and 3.9 × 10¹⁷«s» or 4 × 10¹⁷«s»

[3 marks]

a.

non-accelerated/uniform rate of expansion

OR

H₀ constant over time

OWTTE

[1 mark]

b.

z « = $\frac{v}{c}$ » = $\frac{{4.6 \times {{10}^4} \times {{10}^3}}}{{3.00 \times {{10}^8}}}$ = 0.15

$\frac{R}{{{R_0}}}$ = «z + 1» = 1.15

$\frac{{{R_0}}}{R}$ = « $\frac{1}{{1.15}}$ =» 0.87

OR

87% of the present size

[3 marks]

c.

Examiners report

[N/A]

a.

[N/A]

b.

[N/A]

c.

Syllabus sections

Option D: Astrophysics » Option D: Astrophysics (Core topics) » D.3 – Cosmology

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Option D: Astrophysics » Option D: Astrophysics (Core topics)

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