Question

Write short notes on:

(1) Ultrasound

(2) SONAR

(3) Reverberation

Answer 1

(1) Ultrasounds:

Ultrasounds are high-frequency sound waves that cannot be heard or sensed by humans. Its frequency is greater than 20,000 Hz. These are so energetic that they can penetrate human muscles. These ultrasonic waves can be used for various practical purposes.

Applications of Ultrasounds

(a) Echocardiography is a technique of studying the structure and motion of the heart using ultrasound. The information is used to detect a flaw in the patient’s heart.

(b) Ultrasound is also used to monitor the different developmental stages of a foetus inside a womb.

(c) Ultrasound is used for welding plastic surfaces.

(2) SONAR:

SONAR is an acronym for Sound Navigation And Ranging. It is a technique used to determine the depth, direction, and speed of underwater objects such as submarines and ship wrecks with the help of ultrasounds. It is also used to measure the depth of seas and oceans.

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 sea water. The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is then converted into electrical signals. The distance (d) of the underwater object, calculated from the time (t) taken by the echo to return with speed (v), is given by 2d = v × t. This method of measuring distance is also known as ‘echo-ranging’.

(3) Reverberation:

Persistence of sound (after the source stops producing sound) due to repeated reflection is known as reverberation. As the source produces sound, it starts travelling in all directions. Once it reaches the wall of a room, it is partly reflected back from the wall. This reflected sound reaches the other wall and again gets reflected partly. Due to this, sound can be heard even after the source has ceased to produce sound.

To reduce reverberations, sound must be absorbed as it reaches the walls and the ceiling of a room. Sound absorbing materials such as fibreboard, rough plastic, heavy curtains, and cushioned seats can be used to reduce reverberation.