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Class 9, Science, Chapter-11, Lecture-6, Human Ear (Notes)

SONAR:

Sonar stands for SOund NAvigation and Ranging. 

The SONAR technique is used to determine the depth of the sea and to locate underwater hills, valleys, icebergs, submarines, sunken ships etc.

A beam of ultrasonic sound is produced and transmitted by the transducer (it is a device that produces ultrasonic sound) of the SONAR, which travels through seawater. Ultrasound is reflected by seawater. The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is converted into electrical signals. Using the time taken for echo to come back, we can find the depth of the sea.

The distance (d) of the underwater object is calculated from the time (t) taken by the echo to return with speed (v) is given by 2d = v X t.

This method of measuring distance is also known as ’echo-ranging’.

Echo ranging: 

Echo ranging is the process of finding distances using ultrasound.

HUMAN EAR:

Structure of Human Ear
The human ear can be divided into three main parts, viz. external ear, middle ear and internal ear.

Outer Ear: The outer ear is outside the body and is also called pinna. It extends into the ear canal. The ear canal is filled with air.

Middle Bar: The middle ear is composed of the ear drum or tympanum (it is an elastic membrane, circular in shape) and the bone ossicles (the hammer, the anvil and the stirrup).

Internal Ear: The internal ear is composed of a cochlea and three semi-circular canals.

Diagram of Human Ear showing Stirrup, Anvil and Hammer

Working of Human Ear:

The outer ear called pinna collects the sound waves. 
The sound waves passes through the ear canal to a thin membrane called eardrum. 
The eardrum vibrates. The vibrations are amplified by the three bones of the middle ear called hammer, anvil and stirrup. The middle ear then transmits the sound waves to the inner ear. 
In the inner ear the sound waves are converted into electrical signals by the cochlea and sent to the brain through the auditory nerves. 
The brain then interprets the signals as sound.