Question 1 Why we do not hear the screams of a bat?
Question 2 What is the name of very high frequency sound which cannot be heard by human ears?
Question 3 What is an audible sound?
Question 4 What is an inaudible sound?
Question 5 State few uses of ultrasound?
Question 6 What is ultrasound?
Question 7 What is the upper limit of frequency of human hearing ?
Question 8 What is the lower limit of frequency of human hearing?
Question 9 Name one animal which can produce ultrasonic sounds?
Question 10 Name few animal which can produce hear ultrasonic sounds?
Whenever an object vibrates, sound is produced.
When a simple pendulum vibrates, a sound is produced. But the sound produced by a vibrating simple pendulum is not heard by us. This is because the frequency of vibration of a simple pendulum is very low. It may be 2 or 3 hertz only. And our ears cannot hear sounds of such low frequencies. It is an inaudible sound which cannot be heard by us.
An object must vibrate at the rate of at least 20 times per second to be able to produce audible sound.
The sounds having too low frequencies which cannot be heard by human ear are called infrasonic sounds.
Rhinoceros can produce infrasonic sounds having frequency less than 20 hertz. They can also hear infrasonic sounds.
The human ear can hear sounds which have frequencies between 20 hertz and 20,000 hertz. The lower limit of frequency of human hearing is 20 Hertz and upper limit of human hearing is 20000 Hz.
The sounds having too high frequency which cannot be heard by human ear are called ultrasonic sounds. The sounds of frequency greater than 20,000 hertz are called ultrasonic. The ultrasonic sounds cannot be heard by human beings.
The human beings can neither produce ultrasonic sound nor can they hear ultrasonic sounds. But there are some animal which can produce ultrasonic sounds as well as hear ultrasonic sound.
For Example: Bat is an animal which screams at a very high frequency, much beyond the limit of our hearing. That is it produces ultrasonic sound during screaming. We cannot hear the screams of a bat because its screams consists of ultrasonic sounds having a frequency of more than 20,000 hertz. Some other animals like dogs, monkeys, deer and Leopard can also hear ultrasonic sounds.
The sounds having too high frequency which cannot be heard by human beings is also called ultrasound .
They have a greater penetrating power than ordinary sounds. Echoes produced by ultrasound cannot be heard by our ears, they can only be detected by special equipments.
Uses of Ultrasound
(1) Ultrasound is used as a diagnostic tool in medical Science to investigate inside of the human body.
(2) It is used to study the growth of foetus inside the mother womb.
(3) It is used in the treatment of muscular pains and a disease called arthritis.
(4) It is used to measure the depth of sea.
(5) It is also used to locate underwater objects.