Question

Three different vibrating bodies produce three types of sounds X, Y and Z. Sounds X and Y cannot be heard by a man having a normal range of hearing but sound Z can be heard easily. The sound X is used to find faults and cracks in metals. The sound Y is similar to that which is produced during an earthquake before the main shock wave is generated. Name one device which can produce sound like X.
A. Megaphone
B. SONAR
C. Bulb horn.
D. Ear mufflers

Answer 1

Hint- The sound range which is not audible to human beings are the infrasonic sound and ultrasonic sound. Ultrasonic sound is used to find faults and cracks in metals. It is having frequency higher than the audible range of frequency.

Complete step by step solution:
The human ear can hear only sounds having frequency range between $20\,Hz$ to $20,000\,Hz$. This is known as the audible range of frequency. Sound having frequency higher than this frequency is known as ultrasonic sound. Sound having frequency less than this frequency is known as infrasonic sound. Both ultrasonic sound and infrasonic sound cannot be heard by the human ear.

In the question It is given that sound X and Y cannot be heard by men having normal range of hearing. So, X must be either ultrasonic or infrasonic. Then it is given that sound X is used to find faults and cracks in metals. This means that the sound belongs to the ultrasonic range because the ultrasonic waves have small wavelengths so that while passing through metals when they come across the cracks the sound detected will be different from what was incident. So, ultrasonic sounds are commonly used in detecting cracks or faults in metals. Infrasonic sound is not used for detecting cracks because the wavelength of infrasonic sound is very large so they cannot be used to detect the cracks.

The sound Y is said to be similar to that produced before the main shock in an earthquake. This means the sound Y is an infrasonic sound. We are asked to name a device which produces sound like X. That is, we have to name a device which can produce ultrasonic sound. So, the correct answer is SONAR. SONAR is a device which is used to detect the distance of objects underwater. Sonar uses ultrasonic sound to measure the distance of an object. It produces ultrasonic sound. When the sound strikes the object, it gets reflected back. The time taken for the sound wave to come back is noted and using this the approximate distance is calculated.

Hence the correct answer is option C

Note: Remember that the human ear can hear only the sound waves having frequency between $20\,Hz$ to $20,000\,Hz$. The frequency higher than this frequency is known as ultrasonic sound and the frequency which is less than this frequency is known as infrasonic sound. Human ear cannot hear both infrasonic and ultrasonic sounds.