1. Echoes are caused by _______ of sound.   rarefaction   reflection   refraction   Hint Half-n-half Clue   2. Dolphins use infrasonic vibrations to locate objects and their prey.   True   False   3. Sounds travels faster in air as compared to water.   True   False   4. If a flash of lightning is observed in a cloud 2640 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   8   16   24   Half-n-half Clue   5. The upper limit of frequency that can be heard by the average human is about   200 Hz   2000 Hz   200000 Hz   20000 Hz   Half-n-half Clue   6. The sound of thunder is heard 9 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 _______.   36.7 m   73.3 m   1485 m   2970 m   Half-n-half Clue   7. Sound can travel through vacuum.   True   False