An infrasound microphone enables the remote detection of aircraft wake vortices, clear air turbulence, tornadoes, and seismic events at frequencies below:

Correct option is D

The correct answer is (d) 20 Hz
Explanation: • Infrasound refers to sound frequencies below 20 Hz. • These low-frequency waves travel long distances. • Used to detect natural disasters like earthquakes and tornadoes. • Also used for atmospheric studies and aircraft wake monitoring. • Human ears cannot perceive infrasound.
Information Booster: • Infrasound sensors are part of global nuclear test monitoring systems.
Additional Knowledge: (a) 30 Hz → Audible range, not infrasound. (b) 10 Hz → A part of infrasound, but the upper limit is 20 Hz. (c) 5 Hz → Also infrasound, but not the defined boundary.