Question

Write answers the following questions.

(a) Why do we hear musical notes when the strings of a sitar are plucked?

(b) How does a bat find its way in the dark?

(c) What is the sonar system based on?

(d) Why is the sound of a bell smothered when a hand is placed on it?

Answer 1

(a) As we know vibration is necessary for the production of sound. When the strings of a sitar are plucked, sounds of different frequencies are produced and they are mixed with each other, finally producing musical notes. This is the reason why we hear musical notes when the strings of a sitar are plucked.

(b) Bats produce high-pitched ultrasonic squeaks. These high-pitched squeaks get reflected by objects and return to the bat’s ear. From this the bat comes to know about the position of things in its surroundings. In this way bats find their way in the dark.

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

It is based on the reflection of sound.

A beam of ultrasonic sound is produced and transmitted by the transducer (This device produces ultrasonic sound) of the SONAR system, which travels through sea water. The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is 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’.

(d) The sound of a bell is smothered when we place our hand on it because amplitude of the vibration of the bell decreases.