Sound of frequency less than 20hz is called ____ .

SONAR stands for ____ .

Sound frequency more than 20kHz is called ____ .

Rhinoceros, whales and elephants produce which type of sound to communicate?

Dolphins, bats ,rats and porpoises use ____ sounds to communicate.

Hearing aid is used by people who ____ .

Ultrasonic waves reflect form the parts of the heart forming its image is called ____.

SONAR is installed in ____.

A boy shouts standing in front of a hill which is at a distance of 6m from him. He hears an echo after 3 sec. Find the speed of the sound. [use 2d=v×t]