THE DOPPLER EFFECT
3 marks · NormalA table below shows observed red-shift (z) values for different galaxies at increasing distances from Earth.
| Galaxy | Distance (million light-years) | Red-shift (z) |
|---|---|---|
| A | 100 | 0.005 |
| B | 200 | 0.010 |
| C | 400 | 0.020 |
| D | 600 | 0.030 |
Describe the relationship between galaxy distance and red-shift shown in the table.
Suggest what this relationship supports about the universe.
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(a) The table shows that as the distance from Earth increases, the red-shift value increases. This means more distant galaxies have greater red-shifts.
(b) It supports the idea that the universe is expanding (more distant galaxies are moving away faster).
Common mistakes: Not linking increase in red-shift with increase in distance
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Marking points
B1 (a) · 1 mark · States that red-shift increases as distance increases.
B1 (a) · 1 mark · Describes relationship (proportional or direct relationship indicated).
B1 (b) · 1 mark · Links the result to expanding universe or galaxies receding faster the further they are.
Worked solution
a) As the distance of the galaxy increases, so does the red-shift. The further away a galaxy is, the bigger its red-shift value.
b) This supports the idea that the universe is expanding — more distant galaxies are moving away faster, an observation central to the Big Bang theory.