1. If a flash of lightning is observed in a cloud 1650 m away and the speed of sound in air is 330 m/s, then the sound of thunder will be heard _______ s after the flash of lightning.   3   5   10   15   Hint Half-n-half Clue   2. The apparatus used in a ship to find out the depth of the sea underneath is called _______.   tuning fork   bell jar   sonar   Half-n-half Clue   3. Sounds are produced by musical wind-instruments when columns of air are made to vibrate.   True   False   4. Ultrasonic vibrations are used in medicine for imaging internal organs of the human body.   True   False   5. Dolphins use infrasonic vibrations to locate objects and their prey.   True   False   6. The sound of thunder is heard 10 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 _______.   33.0 m   66.0 m   1650 m   3300 m   Half-n-half Clue   7. The repetition of sound which is reflected from an object is referred to as _______.   an echo   the pitch   the amplitude   Half-n-half Clue