An astrophysicist studying a distant galaxy observes the Hα\text{H}_\alphaHα spectral line of hydrogen. In the laboratory, this line has a rest wavelength of 656.3 nm656.3\text{ nm}656.3 nm, but in the spectrum of the galaxy, it is detected at a wavelength of 698.5 nm698.5\text{ nm}698.5 nm.
Assuming the Hubble constant is H0=68 km s−1 Mpc−1H_0 = 68\text{ km s}^{-1}\text{ Mpc}^{-1}H0=68 km s−1 Mpc−1, what is the approximate distance to this galaxy?
1.4×102 Mpc1.4 \times 10^2\text{ Mpc}1.4×102 Mpc
2.7×102 Mpc2.7 \times 10^2\text{ Mpc}2.7×102 Mpc
2.8×102 Mpc2.8 \times 10^2\text{ Mpc}2.8×102 Mpc
4.4×102 Mpc4.4 \times 10^2\text{ Mpc}4.4×102 Mpc
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.