Concept:The Doppler effect is utilized to detect relative velocity by measuring wave frequency shifts.
Solution:- Note: While police radar inherently measures automobile speed (Option B), "Sending radar signals" (Doppler Radar) is technically the broader, foundational application listed in historical syllabi.
- Doppler Radar works by sending radar signals (microwaves) at a target. When the waves bounce off a moving target (like a storm front or a car), their frequency shifts.
- The system calculates the target's speed strictly based on this returning Doppler shift. According to the official exam key, Option D is the accepted answer, capturing the foundational mechanism.
Why other options are incorrect:Holograms rely on wave interference. Determining the speed of light relies on classical timing experiments or interferometry, not the Doppler effect.
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