Question

Which frequency corresponds to ultrasonic waves
a) 15000 Hz
b) 30000 Hz
c) 2500 Hz
d) 10 Hz

Answer 1

Hint: The ultrasonic waves have a frequency much greater than the maximum audible frequency to the human ear. The minimum frequency of sound audible to an adult human is 20 Hz i.e. known as infrasonic sound and the maximum sound audible to the human ear is 20000 Hz i.e. ultrasonic sound. Hence from this information it becomes clear that in which frequency range do the ultrasonic waves exist.

Complete step by step answer:
To begin with let us first understand what are ultrasonic waves,
Ultrasonic waves have a very short wavelength which is why this property is harnessed for its various applications. These waves are generated by the oscillator called the Piezoelectric oscillator. In this process a magnetic field is applied across a ferromagnetic substance. As a result the length of the substance changes and counteracts such that it generates waves which lie in the ultrasonic region. These waves generally have a frequency greater than 20000 Hz.

Hence, the correct answer is option B.

Note:
These ultrasonic waves have a very short wavelength. Apart from that they undergo reflection, refraction, diffraction etc without negligible loss of energy. These properties of the waves are harnessed for different commercial purposes. The bats, whales and many other animals use these waves to navigate. These animals emit the ultrasonic waves and since these waves get reflected on encountering the obstacles, the animals detect the obstacles as well as their prey. One more commonly used commercial application is that these waves are used to detect metal flaws i.e. holes in metals. A suitable range of the ultrasonic wave is taken and passed through the metal. As soon as it detects a hole the wave refracts and its wavelength changes from entering one medium to another. This change in wavelength is detected through a receiver circuit and flaws in metals are detected.