An absorption line from a star has a wavelength of 620.00 nm620.00\ \mathrm{nm}620.00 nm when measured by an observatory with no relative motion between it and the star.
Three uncrewed space observatories measure the same absorption line. At the instant of each measurement, an observatory is moving directly towards the star, moving directly away from the star or is stationary relative to the star.
| Observatory | Observed wavelength in nm |
|---|---|
| A | 619.92 |
| B | 620.15 |
| C | 620.00 |
Explain what the measurements show about the motion of each observatory relative to the star.
Explain which observatory is moving fastest relative to the star and which observatory detects the highest frequency.
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.