GCSE Physics

Ultrasound and SONAR

Let us take a look at a typical question about SONAR and depth at sea:

A ship sends a pulse of ultrasound and receives an echo 0·3 seconds later. If the speed of sound in water is 1500 m/s calculate its depth.
ship using SONAR to find its depth

speed = distance / time
... distance = speed × time
distance = 1500 × 0·3 = 450 m

BUT this is the total distance travelled by the sound - so the depth is half of this.

Depth = 450 / 2 = 225 m

Be careful - when dealing with reflected sound (echoes) exam questions often try to trick you into using the total distance, not the one you want.

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