Experiment 8 — Sound the Ocean Floor

Topic: Physics · Class 9 · Sound: reflection, echo and SONAR

Aim: Measure the depth of the sea bed using an echo (it is 750 m deep).

Daily: Fishing boats find shoals this way, ships map the sea bed, bats hunt in the dark, and doctors look at an unborn baby with ultrasound — all echoes, timed carefully.

Obs: Your calculation gives a depth of

Question: An echo returns after 2 s. To find the distance to the reflector you must…

Exp: The sound travelled to the reflector and back, so the distance is half the total path.

Question: Sound travels fastest in…

Exp: Closely packed particles transmit vibrations quickest.

Question: To hear a distinct echo in air, the reflector must be at least about…

Exp: The ear needs a 0.1 s gap between the two sounds.

Exp: It uses ultrasound echoes to measure distance.

Exp: It travels as compressions and rarefactions.