Which waves are used in SONAR?
- AAudible sound waves
- BRadio waves
- CInfrasonic waves
- DUltrasonic waves
Show answer and explanation
Correct answer: (d) Ultrasonic waves
Explanation
SONAR (sound navigation and ranging) uses ultrasonic waves, sound of frequency above 20,000 Hz, which humans cannot hear.
A ship or submarine sends out ultrasonic pulses. They reflect from the sea bed, a shoal of fish or a submarine, and the echo is received. The time taken gives the distance:
- distance = (speed of sound in water × time) ÷ 2.
Ultrasound is used because it travels in a narrow beam and is not easily absorbed. Bats and dolphins use the same principle (echolocation).