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Sonar and echoes
Beginner
Distance from the echo time.
d = vt/2Distance from the echo delay: d = vt/2. Bats, submarines and depth sounders use it.
A 0.4 s delay in water (1500 m/s) means 300 m.
Divide by 2 because of the round trip.
In more detail
Sonar uses sound pulses and their echoes to find distances and objects underwater. The time for an echo to return gives the distance, using the speed of sound in water.
Real-world uses
- Submarines and ships use sonar to navigate and avoid obstacles.
- Fishermen use fish finders based on sonar echoes.
- A ship's sonar sends a pulse and times the echo from the seabed to find the depth of the water.
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Frequently asked questions
How do I get distance from an echo?
Half the total round-trip time multiplied by the speed of sound.
Why do bats use echolocation?
They emit ultrasonic pulses and use the echoes to find insects in the dark.
Why divide by two in the echo formula?
The sound travels to the target and back, so the time measured is for the round trip, and only half is the distance.
Related topics in Waves & Sound
Range of hearing · Ultrasound · Infrasound · Doppler effect · Doppler with moving source · Doppler with moving observer