1. The three little bones in the middle ear are the _______, the anvil and the stirrup.   eardrum   cochlea   hammer   Hint Half-n-half Clue   2. If a flash of lightning is observed in a cloud 2970 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   9   18   27   Half-n-half Clue   3. The sound of thunder is heard 7 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 _______.   47.1 m   94.3 m   1155 m   2310 m   Half-n-half Clue   4. The process by which sound vibrations are produced in pipes is known as _______.   rarefaction   refraction   resonance   reflection   Half-n-half Clue   5. An airtight bell-jar is inverted on a platform connected to a vacuum pump. An electric bell fitted into the jar is operated but its sound cannot be heard. This is because sound cannot travel through _______.   vacuum   air   glass   Half-n-half Clue   6. 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   7. The _______ keeps the pressure in the middle ear the same as the outside air pressure.   Eustachian tube   semicircular canal   eardrum   Half-n-half Clue