Exam-style question
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When is Doppler redshift observed?.
- A.When a source is moving towards the observer
- B.When a source is stationary relative to the observer
- C.When a source is moving away from the observer
- D.When the observer is moving towards the source
Model answer
What a good answer should say
- When a source is moving away from the observer
Explanation
Why this works
Doppler redshift is observed when a source of waves, such as light, is moving away from the observer, resulting in an increase in wavelength and a decrease in frequency. This effect is crucial in cosmology for understanding the expansion of the universe.
In contrast, if the source moves towards the observer, a blueshift occurs, indicating a decrease in wavelength.
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