A spectral line corresponds to a frequency f0 f_0\,f0 when measured in a laboratory on Earth. The same spectral line, when observed in the light from a distant, receding galaxy, has a frequency fff. If the Hubble constant is H0 H_0\,H0 and the speed of light in a vacuum is ccc, which of the following is the correct expression for the distance D D\,D of the galaxy from Earth under non-relativistic assumptions?
D≈c(f0−f)H0fD \approx \frac{c(f_0 - f)}{H_0 f}D≈H0fc(f0−f)
D≈c(f0−f)H0f0D \approx \frac{c(f_0 - f)}{H_0 f_0}D≈H0f0c(f0−f)
D≈cfH0(f0−f)D \approx \frac{c f}{H_0 (f_0 - f)}D≈H0(f0−f)cf
D≈cf0H0(f0−f)D \approx \frac{c f_0}{H_0 (f_0 - f)}D≈H0(f0−f)cf0
66 exam-style questions on OCR A A Level Physics Astrophysics and cosmology, covering Stars, Electromagnetic radiation from stars, and Cosmology. Each one has a worked solution and a mark scheme showing where the marks go.