| Date | November 2015 | Marks available | 1 | Reference code | 15N.3.HL.TZ0.3 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Discuss | Question number | 3 | Adapted from | N/A |
Question
This question is about cosmic microwave background (CMB) radiation.
A line in the hydrogen spectrum is measured in the laboratory to have a wavelength of 656 nm. The same line from a distant galaxy is measured to have a wavelength of 730 nm. Assuming that the Hubble constant \({H_0}\) is \({\text{69.3 km}}\,{{\text{s}}^{ - 1}}{\text{Mp}}{{\text{c}}^{ - 1}}\),
calculate the distance of this galaxy from Earth.
discuss why different measurements of the Hubble constant do not agree with each other.
Markscheme
\(\left( {\frac{{\Delta \lambda }}{\lambda } = \frac{v}{c} \Rightarrow } \right){\text{ }}v = \left( {\frac{{3.00 \times {{10}^8} \times 74}}{{656}} = } \right){\text{ }}3.38 \times {10^7}{\text{ (m}}{{\text{s}}^{ - 1}})\);
\(d = \frac{v}{{{H_0}}} = \frac{{3.38 \times {{10}^4}}}{{69.3}} = 488{\text{ Mpc}}\);
measurements from distant galaxies have large uncertainties;
Examiners report
Well done by candidates, weaker candidates did not write their ideas clearly enough in (a)(ii). Part (b) was also quite well done, but only better candidates mentioned uncertainty in measurement of distances to galaxies.
Well done by candidates, weaker candidates did not write their ideas clearly enough in (a)(ii). Part (b) was also quite well done, but only better candidates mentioned uncertainty in measurement of distances to galaxies.
