1. The _______ keeps the pressure in the middle ear the same as the outside air pressure.   semicircular canal   Eustachian tube   eardrum   Hint Half-n-half Clue   2. Sounds are produced by musical wind-instruments when columns of air are made to vibrate.   True   False   3. 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   4. The part of the inner ear shaped like a snail is called the _______.   cochlea   eardrum   hammer   Half-n-half Clue   5. 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   6. When sounds reach the _______ or tympanic membrane, they make it vibrate.   eardrum   cochlea   hammer   Half-n-half Clue   7. The number of sound vibrations per second is called _______.   amplitude   time period   frequency   Half-n-half Clue