1. Sounds are produced by musical wind-instruments when columns of air are made to vibrate.   True   False   2. The _______ keeps the pressure in the middle ear the same as the outside air pressure.   Eustachian tube   semicircular canal   eardrum   Hint Half-n-half Clue   3. The three little bones in the middle ear are the _______, the anvil and the stirrup.   cochlea   hammer   eardrum   Half-n-half Clue   4. The upper limit of frequency that can be heard by the average human is about   200 Hz   20000 Hz   200000 Hz   2000 Hz   Half-n-half Clue   5. An echo from the sea-bed is received 2.50 s after an ultrasonic vibration is sent from a sonar on a ship. If the speed of sound in water is 1500 m/s, then the depth of the sea is _______.   600 m   1875 m   3750 m   7500 m   Half-n-half Clue   6. When sounds reach the _______ or tympanic membrane, they make it vibrate.   eardrum   cochlea   hammer   Half-n-half Clue   7. The apparatus used in a ship to find out the depth of the sea underneath is called _______.   sonar   bell jar   tuning fork   Half-n-half Clue