Astrophysics QWC practice question
Question
Astronomers observe a distant galaxy and measure the wavelength of a specific hydrogen spectral line to be 660 nm. The same hydrogen line, when observed in a laboratory on Earth, has a wavelength of 656 nm.
Explain how these observations provide evidence for the expansion of the universe and estimate the age of the universe.
Student guidance
Write a clear linked explanation using precise physics vocabulary.
Expected physics points
- Key physics ideas:
- Doppler effect and red-shift: Δλ/λ = v/c.
- Link between red-shift and receding galaxies.
- Hubble's Law: v = H₀d.
- Interpretation of Hubble's Law as evidence for an expanding universe.
- Estimation of the age of the universe: t ≈ 1/H₀.
Mark scheme points
- Key physics ideas:
- Doppler effect and red-shift: Δλ/λ = v/c.
- Link between red-shift and receding galaxies.
- Hubble's Law: v = H₀d.
- Interpretation of Hubble's Law as evidence for an expanding universe.
- Estimation of the age of the universe: t ≈ 1/H₀.
Indicative content
- Key physics ideas:
- Doppler effect and red-shift: Δλ/λ = v/c.
- Link between red-shift and receding galaxies.
- Hubble's Law: v = H₀d.
- Interpretation of Hubble's Law as evidence for an expanding universe.
- Estimation of the age of the universe: t ≈ 1/H₀.
- Understanding that the expansion is of space itself, not just galaxies moving through space.
- Level boundaries:
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