Question 19M.3.SL.TZ1.12
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.3.SL.TZ1.12 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Determine, Outline, State | Question number | 12 | Adapted from | N/A |
Light from a distant galaxy observed on Earth shows a redshift of 0.15.
Outline what is meant by redshift.
[1]
«the received» wavelength is longer than that emitted ✔
Allow context of Doppler redshift as well as cosmological redshift.
Redshift. Surprisingly many candidates had problems outlining the meaning of redshift.
Determine the distance to this galaxy assuming a Hubble constant of H0 = 72 km s–1 Mpc–1.
[2]
v = zc = 0.15 × 3.0 × 105 = 4.5 × 104 «km s−1» ✔
d = = 625 «Mpc» ✔
Award [2] for bald correct answer.
Accept in other units, eg, 1.95 x 1025m.
The distance to the galaxy was well calculated by most of the candidates, but some wrote unrealistic answers, such as 650 m. Also, many candidates made obvious POT errors, especially when working between metres and kilometres.
The cosmic microwave background (CMB) radiation provides strong evidence for the Big Bang model. State the two main pieces of this evidence.
[2]
the radiation has a black body spectrum/it is black body radiation ✔
the radiation is highly isotropic/uniform ✔
matched the «predicted» wavelength/temperature if the Big Bang had increased/cooled by expansion ✔
In (b)(i), most of the candidates were focused only on one piece of evidence – generally “isotopic or uniform”, or “discussing wavelength or temperature in light from an expanding universe”. Very few mentioned CBM as having black-body radiation characteristics.
The graph shows the variation of the intensity I of the CMB with wavelength λ.
Determine, using the graph, the temperature of the CMB.
[2]
peak wavelength read off graph as (1.1±0.05)«mm» ✔
substitution into Wien’s law to get T = (2.5 to 2.8)«K» ✔