12
Study of Sound
MPORTANT POINTS:
the particles of the medium oscillate about their moman positions in action para to propagation of the wave, then the wave is called fongitudinal wave If the particles of the medium oscillate about their mean position in a direction perpendicular to the propagation of the wave, then the wave is called transverse wave > Sound waves are longitudinal waves which comprise of compressions and rarefactions >The distance between the consecutive compressions or consecutive actions d wavelength of the sound wave and it is denoted by 2. The Spil of eng The number of cycles taking place per second is called the frequency of the (Greek letter nu). Its SI unit is Hertz ▸ The difference between the extreme value and mean value of the prudely its len amplitude of the sound wave. It is denoted by A. ▸ Frequency determines the pitch of the sound whereas amplitude determines the loudness of sound. ▸ The time taken to complete one cycle is called time period. It is denoted by Tand the uni The distance covered by a point on the wave in unit time is the velocity of the sound wave given by the relations: v frequency x wavelength of v ▸ Velocity of sound in a gaseous medium is proportional to the square root of temperare
****SPECIMEN QUESTIONS ****
(1) The distance between two consecutive compressions is
(1) 슬
(2)
(3) 2
(4)22
Explanation: The distance between two consecutive compressions is the wavelength of the wave. .
. Option 3 is correct.
(2) If time period of a wave is 0.01 sec then the frequency of the wave must be (1) 100 Hz (2) 10 Hz (3) 1 Hz (4) 0.001 Hz (3
Explanation: Frequency= 1 1 T 0.01 = 100 Hz. ..
Option 1 is correct.
(3) Wavelength of a sound wave is 3 m and the frequency is 100 Hz. What is the velocity of the sound? (4 (6 (1) 33.33 m/s (2) 103 m/s (3) 0.03 m/s (4) 300 m/s
Explanation: Velocity = wavelength x frequency. So, velocity= 3 x 100 = 300 m/s. ..
Option 4 is correct.
(4) At an echo point, the echo is heard after 1 sec. What is the distance of the reflecting surface from the source of the sound? (Velocity of sound = 336 m/s) (1) 336 m (2) 168 m (3) 33.6 m (4) 672 m
Explanation: Distance = Velocity x time = 336 x 1 = 336 m. So, the distance travelled by the sound is 336 m. The distance of thereflecting surface must be half of it. ...
Option 2 is correct.
**QUESTIONS FOR PRACTICE
(1) If the direction of oscillations of the particles of the medium is parallel to the propagation of wave, then the wave is called of e
(1) transverse wave
(2) longitudinal wave
(3) mechanical wave
(4) electromagnetic wave
Ana-(2) longitudinal wave
(2) The velocity of sound in gaseous medium is than in solid medium.
(1) more
(2) double
(3) less
(4) half
Ana-(3) less
(3) If the temperature of the gaseous medium is doubled at constant pressure, the velocity of the sound will be
(1) 2 times
(2) 4 times
(3) half
(4) √2 times
Ana-(4) √2 times
(4) A sound has the frequency of 16000 Hz. What type of sound can it be called?
(1) Audible sound
(2) Ultrasound
(3) Infrasound
(4) None of these
Ana-(1) Audible sound
(5) Which of the following animals cannot produce ultrasound?
(1) Bats
(2) Humans
(3) Mice
(4) Dolphins
Ana-(2) Humans
(6) The sound generated by the vibrations of the earth's crust just before an earth quake is an example of
(1) Audible sound
(2) Ultrasound
(3) Infrasound
(4) High pitch sound
Ana-(3) Infrasound
(7) Gases A and B have molecular weights 2 and 32 respectively. If other physical conditions are same, which of the following statement is correct?
(1) Velocity of sound in gas A is one sixteenth of that in gas B
(2) Velocity of sound in gas A is one fourth of that in gas B
(3) Velocity of sound in gas A is four times of that in gas B
(4) Velocity of sound in gas A is 16 times of that in gas B
Ana- (3) Velocity of sound in gas A is four times of that in gas B
(8)The unit of frequency in SI is_____
(1) Hertz
(2) Newton
(3) Watt
(4) metre
Ana-(1) Hertz
(9) Wavelength of a wave is 1.5 m and the frequency is 200 Hz. What is the velocity of the wave?
(1) 133.33 m/s
(2) 300 m/s
(3) 201.5 m/s
(4) 150 m/s
Ana- (2) 300 m/s
(10) The sound of which of the following frequencies can be called as ultrasound?
(1) 19000 Hz
(2) 12500 Hz
(3) 15 Hz
(4) 35000 Hz
Ana- (4) 35000 Hz
(11) The difference between the highest value and the mean value of density or pressure in a sound wave, is called of the wave.
(1) frequency
(2) amplitude
(3) wavelength
Ana- (4) time period
amplitud
(12) What should be the minimum distance of the reflecting surface if a distinct echo is to be heard. (velocity of sound 338 m/s)
(1) 17 m
(2) 17.2 m
(3) 16.9 m
(4) 33.8
Ana- (3) 16.9 m
(13) Sound wave is a wave.
(1) longitudinal
(2) transverse
(3) electromagnetic
(4) magnetic
Ana-(1) longitudinal
(14) Pitch of the sound is dependent on-
(1) frequency
(2) amplitude
(3) wavelength
(4) temperature
Ana-(1) frequency
(15) Echocardiography is based on the reflection of
(1) infrasound
(2) audible sound
(3) ultrasound
(4) light
Ana-(3) ultrasound
(16) To determine the depth of seabed technique can be used.
(1) Sonography
(2) Echocardiography
(3) X-ray
(4) SONAR
Ana-(4) SONAR
(17) converts vibrations into electrical signals in human ear.
(1) Pinna
(2) Eardrum
(3) Stapes
(4) Cochlea
Ana-(4) Cochlea
(18) In SONAR, a signal transmitted by the ship towards the seabed is received back in 5 seconds. If the speed of the sound in water is 1530 m/s, what is the depth of sea?
(1) 3.825 km
(2) 7.650 km
(3) 38.25 km
(4) 76.50 km
Ana-(1) 3.825 km
(19) Which of the following statements is true? (1) Frequency of note Re is more than the frequency of note Ma of the same octave.
(2) Frequency of note Pa is more than the frequency of note Ni of the same octave.
(3) Frequency of note Dha is less than the frequency of note Ni of the same octave.
(4) Frequency of note Ga is more than the frequency of note Ma of the same octave.
Frequency of note Dha is less than the Ana-(2)frequency of note Ni of the same octave.
(20) If frequency of a wave is 20 Hz, its time period must be
(1) 20 s
(2) 0.05 s
(3) 10 s
(4) 0.5 s
Ana- (2) 0.05 s
Hints for difficult questions)
(3) The velocity of sound in gaseous medium is directly proportional to the square root of temperature. So, if temperature is doubled, the velocity will be √2 times.
Option is correct.
(7) The velocity of sound in gaseous medium is inversely proportional to the square root of molecular weight. Here, molecular weight of A is one sixteenth of that of B, so velocity in A will be four times that in B. .
..Option is correct.
(9) Velocity=wavelength x frequency = 1.5 x 200 = 300 m/s. Option 2 is correct.
(12) To hear a distinct echo, the reflected sound must come after 0.1 second. It means it should travel a distance of 338 x 0.1 = 33.8 m. So, the distance of reflecting surface must be half of this
. Qis correct
(18) Signal is received in 5 sec. It means sound has travelled 1530 x 5 = 7650 m. The depth must be half of it. So, depth = 3825 m = 3.825 km. ip 5 ter
Option 1 is correct.
(20) Time period=correct. 1 1 = = 0.05 s. Frequency
..Option 2 is correct.
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