| Date | May 2015 | Marks available | 3 | Reference code | 15M.3.HL.TZ1.5 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
This question is about Hubble’s law.
The light from distant galaxies is red-shifted. Explain how this red-shift arises.
The graph shows the variation of recession speed with distance from Earth for some galactic clusters.
(i) Calculate, in s−1, the Hubble constant..
(ii) Estimate, in s, the age of the universe.
(iii) State the assumption that you made in your estimate in (b)(ii).
Markscheme
(fabric of the) universe is expanding;
so the wavelength of the light increases;
during the time it has traveled from emitter to detector;
(i) correct substitution into \({H_0} = \frac{v}{d}\);
2.7×10-18 (s-1);
(ii) \(\frac{1}{{2.7 \times {{10}^{ - 18}}}} = 3.8 \times {10^{17}}\) (s)/3.7×1017;
Allow ECF from (b)(i).
(iii) universe has always had a constant rate of expansion;
