Sound

THE FREQUENCY RANGE OF HEARING IN HUMANS

Frequency range of hearing is the range of frequency from 20 Hz to 20,000 Hz.

INFRASONIC SOUNDS:

• The sounds of frequencies lower thanhertz are infrasonic sounds.
• Infrasonic sounds cannot be heard by human beings.
• For example, Earthquakes, and some animals like whales, elephants and rhinoceroses produces infrasonic sounds.

ULTRASONIC SOUNDS:

• The sounds of frequencies higher than 20,000 hertz are known as ultrasonic sounds.
• The ultrasound is reflected just like ordinary sound waves and produces echoes.
• Ultrasonic sounds cannot be heard by human beings.
• For example, Dogs can hear ultrasonic sounds of frequency up to 50,000 hertz.

WHY IS THE SCREAM OF BATS INAUDUBLE?

Screams of bat is not audible to humans because bats scream consist of ultrasonic sound having a frequency much higher than 20,000 hertz.

APPLICATIONS OF ULTRASOUND

Ultrasound is used in

(i) Detection of Cracks and Flaws
(ii) Lithotripsy
(iii) Cleaning
(iv) Sonar apparatus
(v) Ultrasonography
(vi) Echolocation

ULTRASOUNDS IN DETECTION OF CRACKS AND FLAWS

Ultrasound is used to detect cracks and flaws in metal blocks that are used in the construction of high rise structures such as buildings and bridges.

Process: The high frequency sound waves of the ultrasound reflect from flaws in predictable ways, producing distinctive echo patterns that can be displayed and recorded by portable instruments. An operator identifies specific echo patterns corresponding to the echo response from good parts. From the representative flaws, ultrasonic sounds generate an ultrasonic waveform is interpreted by a trained operator with the aid of analysis software. The software locates and categorizes flaws in test pieces by comparing to the patterns from calibration standards to determine the condition of the metal.

LITHOTRIPSY:

Lithotripsy is the process of breaking stones in the kidney by using ultrasound.

Process: Ultrasonic waves are passed through the body to break up stones in the kidney, bladder, or ureter (tube that carries urine from your kidneys to your bladder). After the procedure, the tiny pieces of stones pass out of your body in your urine.

ULTRASOUND IN CLEANING INDUSTRY

Ultrasound is used in industry to clean ‘hard to reach’ parts of objects such as spiral tubes, odd-shaped machines and electronic components. The object is dipped in a solution of suitable cleaning material and ultrasonic waves are passed into it. As a result of this, high frequency waves are generated that cause the dirt and grease to detach from the surface.

ULTRASOUND IN SONAR APPARATUS

• Ultrasound is used in ‘sonar’ apparatus to measure the depth of sea (or ocean); and to locate under-sea objects like shoal of fish, shipwrecks, submarines, sea-rocks and hidden ice-bergs in the sea.

• Ultrasound scans are used to monitor the development of fetus (unborn baby) inside the mother’s uterus

ULTRASONOGRAPHY:

Medical ultrasound is a diagnostic imaging technique based on ultrasound for the imaging of internal body structures such as muscles, joints and internal organs.
Ultrasonic images are known as sonograms.
Ultrasonography helps to study the development of the fetus during pregnancy, to detect any abnormalities

ECHOCARDIOGRAPHY

Echocardiography helps the doctors to study the condition of the heart of the patient. Here, the ultrasonic waves are used to form an image of the heart using reflection.

Echolocation:

• Echolocation is the process where sound waves and echoes are used to determine objects in space.
• This phenomenon is used by bats to navigate and find their food in the dark.

HOW BATS HUNT FOR FOOD?

During flight, a bat emits ultrasonic waves. The bat receives these waves after being reflected by the obstacle in its path. From the time interval between transmission and reception of ultrasonic waves, the bat gets information about the distance, nature of obstacle and its direction of location. Hence bats can move about freely even in total darkness.

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