Sound

51. What is the audible range (hearing range )of humans ? [M.P.P.C.S.(PRE) 2018]

(a) 20 Hz-20000 Hz.
(b) 80 Hz - 100 Hz.
(c) 2 lac Hz - 4 lac Hz.
(d) 0 Hz - 20 Hz.

Correct Answer: (a) 20 Hz-20000 Hz.

Solution:The sound that can be audible to humans has a frequency ranging from 20 Hz to 20000 Hz.

52. What is/are not true among the following? [Chhattisgarh P.C.S.(PRE) 2022]

(1) Audible range of sound for human being approximately 20 Hz to 10 kHz.
(ii) Sound waves with frequencies higher than 10% are called ultrasound.
(iii) In earthquake, ultrasounds are produced before main shock waves.

(a) i and ii
(b) i and iii
(c) i,ii, and iii
(d) only iii

Correct Answer: (c) i,ii, and iii

Solution:Audible sound range for human beings is approximately 20 Hz to 20 kHz (20,000 Hz). Sound waves with frequencies higher than 20 kHz (20,000 Hz) are called ultrasonic waves (ultrasound). In earthquake, infrasounds (less than 20 Hz) are produced before main shock waves. Hence, all three statements are incorrect.

53. A biotechnique in which ultrasonic sound is used: [R.A.S/R.T.S (PRE) 2012]

(a) sonography
(b) E.C.G
(c) E.E.G
(d) X.ray

Correct Answer: (a) sonography

Solution:Sonography or ultrasonography is an important mean of clinical diagnosis. It is a diagnostic imaging technique based on the application of ultrasound (ultrasonic waves). It is widely used in the field of medical science. It is mainly used to provide a variety of information about the health of the mother during pregnancy, and the health and development of embryo or foetus.

54. Which of the following rays/waves are used to know the growth of fetus in the womb ? [67th B.P.S.C. (PRE) 2022]

Correct Answer: (c) Ultrasonic waves

55. Bats can fly during dark nights and also prey.This is because : [U.P.P.C.S.(MAINS) 2005]

(a) the pupil of their eyes is large.
(b) their night vision is very good.
(c) every bird can do this.
(d) they produce ultrasonic waves and are guided by them.

Correct Answer: (d) they produce ultrasonic waves and are guided by them.

Solution:Bats are a fascinating group of animals. They are one of the few mammals that can use ultrasonic sound to navigate. As they fly, make an ultrasonic (shouting) sound. The returning echoes give the bats information about anything that is ahead of them, including the speed and size of an insect and which way it is going. This system of finding prey is echolocation -locating things by their echoes.

56. Consider the following statement : [U.P.P.C.S. (Mains) 2002]

1. The heart vibrates at infrasonic.
2. The speed of sound is more in gas than in liquid and solid.
3. Mach number is used to describe the speed of sound.
4. Ultrasonic sound has frequency more than 20,000 Hz.
Of these statements:

(a) 1,2 and 3 are correct
(b) 2,3 and 4 are correct
(c) 1,3 and 4 are correct
(d) 1,2 and 4 are correct

Correct Answer: (c) 1,3 and 4 are correct

Solution:The heart vibrates at infrasonic sound. We can hear them with the help of stethoscope. The speed of sound in solid is maximum. Mach number is a quantity that defines how quickly an object travels with respect to the speed of sound.

The Mach number (M) is simply the ratio of the object's velocity (V) divided by the speed of sound at the altitude (a). Ultrasonic is the name given to sound waves that have frequencies greater than 20000 Hz Therefore statement 1, 3 and 4 are correct.