A line in the spectrum of hydrogen has a wavelength of 656 nm when measured in a laboratory. In the light from a distant galaxy the same line is measured at 669 nm.
(a) Calculate the speed at which the galaxy is moving away from the Earth. The speed of light is $3.0 \times 10^{8}$ m/s. [3]
(b) Explain how observations of red-shift from many galaxies support the Big Bang theory. [2]
(c) Name one other piece of evidence for the Big Bang theory. [1]
- (a) change in wavelength = 669 − 656 = 13 nm(1)
- (a) substitution: $\dfrac{13}{656} = \dfrac{v}{3.0 \times 10^{8}}$(1)
- (a) $5.9 \times 10^{6}$ m/s accept 5.95 × 106 m/s or 5 945 000 m/s; 5.8 × 106 m/s (669 used as denominator) scores 1 mark(1)
- (b) light from (almost all) galaxies is red-shifted, so they are moving away from us allow more distant galaxies have a greater red-shift / are moving away faster(1)
- (b) so the Universe is expanding, (suggesting) it started from a single point / a very small, hot, dense state(1)
- (c) cosmic microwave background (CMB) radiation accept CMBR; 'microwave background' alone is enough(1)
- Answer: (a) $5.9 \times 10^{6}$ m/s (b) galaxies receding, further ones faster, so Universe expanding from a point (c) CMB radiation
- Examiner tip: Use the change in wavelength over the ORIGINAL (laboratory) wavelength, not the observed one.