1. The repetition of sound which is reflected from an object is referred to as _______.   the amplitude   an echo   the pitch   Hint Half-n-half Clue   2. A _______ note is the lowest note obtained on blowing gently across the top of a test-tube.   fundamental   overtone   harmonic   Half-n-half Clue   3. Ultrasonic vibrations are used in medicine for imaging internal organs of the human body.   True   False   4. 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   5. Sound can travel through vacuum.   True   False   6. 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 _______.   air   glass   vacuum   Half-n-half Clue   7. Echoes are caused by _______ of sound.   refraction   reflection   rarefaction   Half-n-half Clue