1. Out of the following materials, the best conductor of sound is _______.   Air   Steel   Water   Hint Half-n-half Clue   2. Sounds are produced by musical wind-instruments when columns of air are made to vibrate.   True   False   3. Ultrasonic vibrations are used in medicine for imaging internal organs of the human body.   True   False   4. The three little bones in the middle ear are the _______, the anvil and the stirrup.   hammer   eardrum   cochlea   Half-n-half Clue   5. 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   6. When sounds reach the _______ or tympanic membrane, they make it vibrate.   hammer   eardrum   cochlea   Half-n-half Clue   7. A _______ note is the lowest note obtained on blowing gently across the top of a test-tube.   overtone   harmonic   fundamental   Half-n-half Clue