A surface receiving sound is moving from its original position to a position three times farther away from the source of the sound. the intensity of the received sound thus becomesA. three times as high. b. nine times as high. c. nine times as low. d. three times as low

Sound spreads out in area, and area is proportional to

the square of the distance.

Move the surface to three times the original distance,

and the intensity of the received sound becomes 1/9 of

the original intensity.

(The phrases "three times farther" and "nine times as low"

are awkward and mathematically meaningless.)