RAS question
Doppler effect is used in which of the following applications?
Correct answer: (D) Radar speed guns, medical ultrasound, and weather radar.
The Doppler effect is used in radar speed guns, medical ultrasound and weather radar.
Explanation
The Doppler effect is a change in observed frequency caused by relative motion, so the same principle can serve different instruments: police radar speed guns measure speed, medical Doppler ultrasound measures blood flow, and weather Doppler radar tracks storms and cyclones. The National Weather Service page explains the weather-radar case clearly: its NEXRAD system sends out radar energy, receives the reflected signal from moving precipitation, and reads the frequency shift to determine speed. That is why option D is the only complete choice. The other options fail because they restrict the effect to a single setting, and astronomy and satellite communication are also applications.
Why the other options are wrong
- (A) Only musical instruments is wrong because Doppler effect applications include radar speed guns, medical Doppler ultrasound, weather radar, astronomy and satellite communication, so the effect is not confined to musical instruments.
- (B) Only submarines is wrong because the Doppler effect has several non-submarine applications, including radar speed guns, blood-flow measurement and weather radar.
- (C) Only telescopes is wrong because astronomy is only one listed use, while Doppler-based radar and ultrasound applications also depend on frequency change due to relative motion.
Concept
This tests applied wave physics: identifying the Doppler effect as a frequency shift due to relative motion and linking it to technologies rather than memorising one device. In RAS-style science MCQs, the recurring trap is the word only, because one principle can appear across policing, medicine, weather monitoring and astronomy.