A prominent absorption line in the spectrum of a distant galaxy is identified as the hydrogen-alpha (HαH_\alphaHα) line. In a laboratory on Earth, this line has a wavelength of 656 nm656\text{ nm}656 nm, but in the galaxy's spectrum, it is observed at 682 nm682\text{ nm}682 nm.
Assuming the Hubble constant H0=68 km s−1 Mpc−1H_0 = 68\text{ km s}^{-1}\text{ Mpc}^{-1}H0=68 km s−1 Mpc−1 and the speed of light c=3.00×108 m s−1c = 3.00 \times 10^8\text{ m s}^{-1}c=3.00×108 m s−1, what is the approximate distance to this galaxy?
168 Mpc168\text{ Mpc}168 Mpc
175 Mpc175\text{ Mpc}175 Mpc
4590 Mpc4590\text{ Mpc}4590 Mpc
1.75×105 Mpc1.75 \times 10^5\text{ Mpc}1.75×105 Mpc
53 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift. Each one has a worked solution and a mark scheme showing where the marks go.