1. The apparatus used in a ship to find out the depth of the sea underneath is called _______.   bell jar   tuning fork   sonar   Hint Half-n-half Clue   2. The sound of thunder is heard 8 s after the flash of lightning. If the speed of sound in air is 330 m/s, then the cloud is at a distance of _______.   41.2 m   82.5 m   1320 m   2640 m   Half-n-half Clue   3. The _______ keeps the pressure in the middle ear the same as the outside air pressure.   semicircular canal   Eustachian tube   eardrum   Half-n-half Clue   4. The lower limit of frequency that can be heard by the average human is about   2 Hz   20 Hz   200 Hz   2000 Hz   Half-n-half Clue   5. Ultrasonic vibrations are used in medicine for imaging internal organs of the human body.   True   False   6. The repetition of sound which is reflected from an object is referred to as _______.   the pitch   an echo   the amplitude   Half-n-half Clue   7. Echoes are caused by _______ of sound.   refraction   rarefaction   reflection   Half-n-half Clue