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CAIE A-Level Physics 25.3 Hubble's Law and the Big Bang

Practise quantifying redshift, calculating recession speed with spectral data, applying Hubble’s law and linking expansion evidence to the Big Bang.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • identify and quantify redshift by comparing observed and known spectral lines
  • use ??/? ? ?f/f ? v/c to determine recession speed or spectral shift
  • explain how redshift observations support an expanding Universe
  • use Hubble?s law to calculate cosmic distance or recession speed and relate it to the Big Bang

Covered syllabus points

25.3.1—The lines in the emission and absorption spectra25.3.2—Redshift of electromagnetic radiation25.3.3—Why redshift leads to the idea that the universe is expanding25.3.4—Hubble’s law v ≈ H0d and explain how this leads to the Big Bang theory

25.3 Hubble’s law and the Big Bang theory question 1

[Maximum number: 4]

Question (a)

(a)

The lines in Fig. 10.1 have been corrected for redshift.

[ 4 ]

Question (i)

(i)

State what is meant by redshift.

[ 2 ]

Question (ii)

(ii)

Explain how cosmologists are able to determine that light from a distant star has undergone redshift.

[ 2 ]

25.3 Hubble’s law and the Big Bang theory question 2

[Maximum number: 6]

Question (a)

(a)

A spectral line from a star within a galaxy is observed to have a wavelength of 660.9 nm . The same spectral line measured in the laboratory is observed to have a wavelength of 656.3 nm .

[ 6 ]

Question (i)

(i)

Show that the speed of the star relative to the Earth is 2.1×106 ms−12.1 \times 10^{6} \mathrm{~ms}^{-1}.

[ 1 ]

Question (ii)

(ii)

Calculate the distance to the star.

The Hubble constant is 2.3×10−18 s−12.3 \times 10^{-18} \mathrm{~s}^{-1}.
distance = m

[ 2 ]

Question (iii)

(iii)

State and explain what can be concluded about the Universe based on this change in observed wavelength.

[ 3 ]
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