IGCSE · 6 · data analysis
Space physics · Question 10
Space physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 12
- Topics
- 1
- Answer
- Complete
Astronomers measure the speed at which distant galaxies are moving away from the Earth and the distance to each galaxy. The table gives values for four galaxies.
| galaxy | distance d / 10²⁴ m | speed of recession v / 10⁶ m/s |
|---|---|---|
| P | 1.2 | 2.6 |
| Q | 3.5 | 7.7 |
| R | 6.0 | 13.2 |
| S | 9.4 | 20.7 |
- (a)
Describe Describe the relationship between the speed of recession and the distance shown by the table.
2 marks - (b)
Determine Determine a value for the Hubble constant H₀ from these data, and give its unit.
3 marks - (c)
Estimate Use your value of H₀ to estimate the age of the Universe. Give your answer in seconds.
2 marks - (d)
Explain Explain how the relationship in (a) supports the idea that the Universe began with the Big Bang.
3 marks - (e)
Suggest The astronomers measured only four galaxies. Suggest two reasons why a value of H₀ obtained this way is less reliable than one obtained from several hundred galaxies.
2 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Describe Describe the relationship between the speed of recession and the distance shown by the table.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
the speed of recession increases as the distance increases
- 2
and the increase is proportional — v/d is the same for all four galaxies
(b)
Determine Determine a value for the Hubble constant H₀ from these data, and give its unit.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
H₀ = v / d
- 2
using galaxy S: H₀ = 20.7 × 10⁶ / 9.4 × 10²⁴
- 3
H₀ = 2.2 × 10⁻¹⁸, unit s⁻¹ (per second)
(c)
Estimate Use your value of H₀ to estimate the age of the Universe. Give your answer in seconds.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
age ≈ 1 / H₀
- 2
age ≈ 1 / 2.2 × 10⁻¹⁸ = 4.5 × 10¹⁷ s
(d)
Explain Explain how the relationship in (a) supports the idea that the Universe began with the Big Bang.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
every distant galaxy is moving away from us, and the further away it is the faster it recedes, so the Universe is expanding
- 2
tracing the motion backwards, all the galaxies were once much closer together
- 3
so the expansion began from a single point at a definite time in the past
(e)
Suggest The astronomers measured only four galaxies. Suggest two reasons why a value of H₀ obtained this way is less reliable than one obtained from several hundred galaxies.
Read the data before explaining it. Quote the relevant values or trend, show the comparison or calculation, and then connect that numerical evidence to the physical conclusion—including uncertainty or anomalies when they matter.
- 1
the distance to a galaxy is very difficult to measure and carries a large uncertainty, so a value from four galaxies depends heavily on whether those four happen to be well measured
- 2
galaxies also have their own motion within their local cluster on top of the expansion, and averaging over many galaxies is what reduces that additional scatter
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