1. Ultrasonic vibrations are used in medicine for imaging internal organs of the human body.   True   False   2. When sounds reach the _______ or tympanic membrane, they make it vibrate.   cochlea   eardrum   hammer   Hint Half-n-half Clue   3. Out of the following materials, the best conductor of sound is _______.   Water   Air   Steel   Half-n-half Clue   4. The number of sound vibrations per second is called _______.   frequency   time period   amplitude   Half-n-half Clue   5. The repetition of sound which is reflected from an object is referred to as _______.   an echo   the amplitude   the pitch   Half-n-half Clue   6. Echoes are caused by _______ of sound.   refraction   reflection   rarefaction   Half-n-half Clue   7. The approximate speed of sound in air is _______ m/s.   5000   1600   330   3 × 108   Half-n-half Clue