SONAR, a device used to measure the distance, direction and speed of underwater objects, uses which type of waves?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Ultrasonic Waves
SONAR (Sound Navigation and Ranging) sends out pulses of ultrasonic waves, sound of frequency above 20,000 Hz, which humans cannot hear. The pulse is reflected by the sea bed, a submarine or a shoal of fish, and the echo is picked up.
The time between sending the pulse and receiving the echo gives the distance: \(\displaystyle d=\frac{v\times t}{2}\), since the sound travels there and back
Ultrasound is used because its short wavelength lets it travel in a narrow beam and reflect from small objects
Why the other options are incorrect
Option (2) Infrasonic Waves — Incorrect. Sound below 20 Hz, given out by earthquakes and elephants; its long waves spread out and cannot pick out small objects.
Option (3) Supersonic Waves — Incorrect. “Supersonic” describes a speed faster than sound, as of a jet, not a kind of wave.
Option (4) Hypersonic Waves — Incorrect. “Hypersonic” means a speed of more than five times the speed of sound, as of some missiles.