Vibration is the cause of producing sound. The fact is that sounds of frequencies less than about 20 vibrations per second cannot be detected by the human ear. Here is the table of data of some animals with their frequency range of sound waves.
| Animal | Frequency range of sound waves |
| Elephant | 15-12000 Hz |
| Human | 20-22000 Hz |
| Dog | 65-45000 Hz |
| Chicken | 125-2000 Hz |
Q.1. A cat made a purring sound that had a frequency of 35 Hz. Which of the animals mentioned in the table can hear the purring?
(a) Only human
(b) Only elephant
(c) Dog and chicken
(d) Elephant and human
Q.2. Which of these will reduce noise pollution?
(a) Regulating the use of loudspeakers
(b) Setting up more thermal power plants
(c) Using more electric vehicles
(d) (a) and (c) both