Question

Sound
3. The frequency of ultrasonics is ...... than the range of human hearing.
4. Sound vibrations die out after travelling some distance due to the loss of ..
5. Sound needs a ...... to travel.
6. Industrial noise can be reduced by proper .......
7. The reflecting surface has to be at least ...... away for us to hear an echo distinctly.
each of the following​

Answer 1

Answer:

3.more 4. energy 5.medium 6. installing silence device 7. 11.3m