Name: Characteristics of a Musical Sound
Uploaded: 2019-07-19
Duration: 7 min 13 s
Description: What makes a sound musical? In this video, we will look at defining the three main characteristics that make a sound musical. Let’s get into it.

Question

What are ultrasonic waves? Write down their applications and properties.

Accepted Answer

Ultrasound or ultrasonic waves are defined as sound waves having a frequency more than $20 kHz$ that exceeds the hearing limit of the human ear . Some animals utilise ultrasound for navigation (dolphins) or hunting (bats) using the information carried by back-scattering sound waves. Ultrasound is one of the emerging technologies that were developed to minimise processing, maximise quality and ensure the safety of food products. Ultrasound is applied to impart positive effects in food processing such as improvement in mass transfer, food preservation, the assistance of thermal treatments and manipulation of texture and food analysis

Properties of ultrasonic waves -

$1$ . High power - Energy per unit time is defined as power. the energy of wave depends on its frequency. Higher the frequency of the wave, greater the energy of the wave. Ultrasonic waves have high frequency, hence their energy, as well as power, is also high. This high power of ultrasonic waves is used in industry and medicine to break and cut objects.

$2$ . Good directionality - These waves are able to travel along well-defined straight paths, even in the presence of obstacles. This means that bending of high-frequency waves at the edge of an obstacle is quite insignificant whereas low-frequency sound waves easily bend around the corners and spread in all directions. This bending of sound waves around the obstacle is called diffraction of sound. For example, you can hear the sound coming from a radio that is placed on one side of any non-transparent medium.

Applications of ultrasonic waves -

$1$ . Drilling holes or making cuts of the desired shape are done using ultrasonic vibrations produced in a metallic rod. This metallic rod is called a horn. The horn hammers the plate about a hundred thousand times per second.

$2$ . Ultrasonic cleaning - It is very difficult to clean parts located 'in hard to reach places', e.g., small parts used in watches. To clean such objects, they are placed in a cleaning solution, and ultrasonic waves are sent into the solutions. Since vibrations are at high frequencies, all dirt and grease particles get detached from the surface and object gets thoroughly cleaned.
$3$ . Ultrasonic detection of defects in metals - The cracks or holes inside a metal is not visible from inside. They can be detected by using ultrasonic waves. Ultrasonic waves are sent through a metal. If there is no defect in the metal, the waves go straight. If there is a crack, the waves get reflected back. The intensity of waves at the detector end is reduced if there is a defect.

$4$ . Imaging by sound - Due to high directionality and capability of reflection from boundaries of different kinds of materials, ultrasound waves are used as a powerful and safe tool for imaging human organs like liver, gallbladder, uterus, etc. It is used to monitor the growth of the foetus in the mother's womb.

$5$ . Treatment of kidney stones - Ultrasonic waves are employed to break stones that form in the kidneys into fine grains. Since the frequencies of these waves are large, they cause the molecules to vibrate vigorously. These vibrations cause stone in the kidney to break into fine grains, which get flushed out with urine.
$6$ . SONAR - SONAR stands for Sound Navigation and Ranging. It is a technique for detecting and finding the distance of objects underwater by means of reflected ultrasonic waves. The device employed for this purpose is called SONAR. A transmitter is installed in a ship. This transmitter sends out ultrasonic waves in the form of pulses at regular intervals of time. These pulses get reflected after striking the obstacles. A receiver is also installed in the ship. The reflected waves are gathered at the receiver.

What are ultrasonic waves? Write down their applications and properties.

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