Question 19M.3.HL.TZ1.20
| Date | May 2019 | Marks available | [Maximum mark: 5] | Reference code | 19M.3.HL.TZ1.20 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Compare and contrast, Draw, Explain | Question number | 20 | Adapted from | N/A |
Light from distant galaxies is redshifted. Explain the cosmological origin of this redshift.
[2]
«according to general relativity» space expands stretching distances between far away objects ✔
wavelengths of photons «received a long time after they were emitted» are thus longer leading to the observed redshift ✔
Do not accept references to the Doppler effect.
Cosmological origin of redshift. The cosmological redshift and variation with time of the cosmic scale factor proved to be a well-mastered concept by many students.
The graph shows the variation with time of the cosmic scale factor R of the universe for the flat model of the universe without dark energy.
Draw, on the axes, a graph to show the variation with time of the cosmic scale factor R for the flat model of the universe with dark energy.
[1]
✔
Cosmological origin of redshift. The cosmological redshift and variation with time of the cosmic scale factor proved to be a well-mastered concept by many students.
Compare and contrast, the variation with time of the temperature of the cosmic background (CMB) radiation, for the two models from the present time onward.
[2]
«since T ∝ » the temperature drops for both models ✔
but in the accelerating model R increases faster and so the temperature drops faster ✔
In (ii) however, many candidates did not directly answer the question, making little to no reference of temperature.