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RANGE OF HEARING (AUDIBLE RANGE)

All vibrating bodies produce waves. Each wave has its own frequency. The frequency of a wave is equal to the frequency of the vibrating body producing sound. When a woman speaks, the waves produced by the vocal cords in her throat have different frequency than the frequency of the waves produced by the vocal cords of a man. Can human ears hear all the frequencies produced by the vibrating bodies ? The answer is No. In fact, normal human ears can hear only those waves whose frequency lies between 20 Hz and 20,000 Hz. The waves having frequency between 20 Hz and 20,000 Hz are known as sound waves. Thus, the audible range of frequency is 20 Hz to 20,000 Hz.

The waves having frequency less than 20 Hz and greater than 20,000 Hz cannot be heard by human ear.

Infrasonics or InFrasound
 The waves of frequency less than 20 Hz are known as infrasonic waves.
 The infrasonic waves are produced by large vibrating bodies.
 For example, infrasonic waves are produced by the vibration of the earth's surface during the earthquake. Some animals like elephants, rhinoseroses and whales etc. also produce infrasonic waves. These waves are not audible to a human ear.
 It has been observed that animals behaviour becomes unusual just before the tremor is felt. This is because the animals has the ability to detect infrasonic waves produced at the time of tremor.

Ultrasonics or Ultrasound

The waves of frequency greater than 20,000 Hz are known as ultrosonic waves or ultrasound. These waves are not audible to a human ear but they can be heard by animals and birds.
 Bats can produce ultrasonic waves by flapping their wings. They can also detect these waves. The ultrasonic waves produced by the bats after reflection from the obstacles like buildings guide them to remain away from the obstacles during their flights. Hence, they can fly during night without hitting the obstacles. Bats also catch their prey during night with the help of ultrasonic waves. The ultrasonic waves produced by a bat spread out. These waves after reflecting from a prey sayan insect reach the bat. Hence, the bat can easily locate its prey.

Dolphins also produce ultrasonic waves. They can also detect the ultrasonic waves. They catch their prey like a fish due to their ability to detect the ultrasonic waves reaching them after reflecting from a fish.

Human Ear and Applications of Sound | Science Class 9

Sonar

SONAR stands for Sound Navigation and Ranging.
 It is a device which is used in the ships to locate rocks, icebergs, submarines, old ships sank in sea ete. It is also used to measure the depth of a sea.

Human Ear and Applications of Sound | Science Class 9

Principle : It is based on the principle of the reflection of sound wave (i.e. echo).
 Determination of the Depth of a Sea using Sonar

A beam of ultrasonic waves from the transmitter of a SONAR fitted on the ship is sent towards the bottom of the sea. This beam is reflected back from the bottom of the sea and is received by the receiver of the SONAR on the ship.

The time taken by the ultrasonic waves to go from the ship to the bottom of the sea and then back to the ship is noted. Let it be 't' seconds. Therefore, the time taken by the ultrasonic waves to go from the ship to the bottom of the sea is t/2 seconds.
 Using the following formula S = v(t/2) we can find the depth of the sea.
 Here, u = speed of ultrasonic wave in water.
 S = depth of the sea

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FAQs on Human Ear and Applications of Sound - Science Class 9

1. What is the structure and function of the human ear?
Ans. The human ear is composed of three main parts: the outer ear, middle ear, and inner ear. The outer ear collects sound waves and directs them into the ear canal. The middle ear consists of the eardrum and three tiny bones called ossicles, which amplify the sound vibrations. The inner ear contains the cochlea, responsible for converting sound waves into electrical signals that are transmitted to the brain for interpretation.
2. How does sound travel through the ear?
Ans. Sound waves enter the outer ear and travel through the ear canal until they reach the eardrum in the middle ear. The eardrum vibrates in response to the sound waves, which then causes the ossicles to vibrate. These vibrations are transmitted to the cochlea in the inner ear, where they are converted into electrical signals and sent to the brain via the auditory nerve.
3. What are some common applications of sound in everyday life?
Ans. Sound has various applications in our daily lives. It is used in communication through speech and language, allowing us to interact and understand each other. We also rely on sound for entertainment purposes, such as listening to music, watching movies, or attending concerts. Sound alarms and sirens are used for safety alerts, while ultrasound technology utilizes sound waves for medical imaging.
4. How does the human ear help in maintaining balance?
Ans. The inner ear plays a crucial role in maintaining balance. It contains the vestibular system, which consists of three semicircular canals and two otolith organs. These structures detect changes in head position and movement, sending signals to the brain to help us maintain balance and posture. The information from the inner ear is combined with visual cues and proprioceptive feedback from muscles and joints to ensure proper balance.
5. Can prolonged exposure to loud noises damage the human ear?
Ans. Yes, prolonged exposure to loud noises can cause damage to the human ear. Continuous exposure to high decibel levels can lead to noise-induced hearing loss, which can be temporary or permanent. It is important to protect our ears from excessive noise by using earplugs or earmuffs, especially in noisy environments or when engaging in activities such as attending concerts or operating loud machinery.
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