A star moves in an orbit around another star. Astronomers measure the wavelength of one of its absorption lines at two different positions, P and Q.
| Measurement | Wavelength / nm\mathrm{nm}nm |
|---|---|
| laboratory | 520.0 |
| position P | 519.4 |
| position Q | 520.9 |
The speed of light is 3.0 × 108 m/s.
Using c=fλc=f\lambdac=fλ, calculate how much the observed frequency changes between position P and position Q.
Explain which observation was made when the star was moving towards the Earth.
94 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.