How do astronomers and radar operators both use a frequency shift to learn about a moving object?
AThey measure the total energy the object has absorbed
BThey measure the polarization angle of the reflected wave
CThey measure how far the object bends incoming light
DThey measure the Doppler shift of the returning waves
Answer & Solution
Correct answer: D. They measure the Doppler shift of the returning waves
1. Radar information comes from receiving and analysing echoes of microwaves reflected by an object.
2. The speed of the object is found from the Doppler shift of the returning waves.
3. Astronomers use the same effect, calling the shift toward lower frequencies a red shift for a receding galaxy.
4. Absorbed energy and bending of light are different phenomena and do not give a moving object's speed this way.
_Source: OpenStax Physics (CC BY 4.0), Ch 15 "Light", section 15.1 The Electromagnetic Spectrum_
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