numerical problems 10th physics chapter 11 sound.
11.1 to 11.9 solution of numerical problems.
NUMERICAL PROBLEMS
11.1. -6 -2 A normal conversation involves sound intensities of about 3.0 × 10 W m . What is
the decibel level for this intensity? What is the intensity of the sound for 100
dB?
Ans. (64.8 dB, 0.01 W m ) -2
11.2. If at Anarkali Bazar Lahore, intensity level of sound is 80 dB, what will be the intensity
of sound there?
-4 -2 Ans. (10 W m )
11.3. -1 At a particular temperature, the speed of sound in air is 330 m s . If the wavelength
of a note is 5 cm, calculate the frequency of the sound wave. Is this frequency in the
audible range of the human ear? 3
Ans. (6.6 x 10
Hz, Yes)
11.4. A doctor counts 72 heartbeats in 1 min. Calculate the frequency and period of the
heartbeats.
Ans. (1.2 Hz, 0.83 s)
11.5. A marine survey ship sends a sound wave straight to the seabed. It receives an
-1 echo 1.5 s later. The speed of sound in seawater is 1500 m s . Find the depth of the
sea at this position. Ans.
(1125 m)
11.6. A student clapped his hands near a cliff and heard the echo after 5 s. What is the
-1 distance of the cliff from the student if the speed of the sound is taken as 346 m s ?
Ans. (865 m)
11.7. A ship sends out ultrasound that returns from the seabed and is detected after
-1 3.42 s. If the speed of ultrasound through seawater is 1531 m s , what is the distance
of the seabed from the ship?
Ans. (2618 m)
11.8. The highest frequency sound humans can hear is about 20,000 Hz. What is the
o
wavelength of sound in air at this frequency at a temperature of 20 C? What is the
wavelength of the lowest sounds we can hear of about 20 Hz? Assume the
O -1 speed of sound in air at 20 C is 343 m s .
35 N
SUMMARY
Sound is produced by a vibrating body. It travels in the medium from one place to
another in the form of compressional waves.
Loudness is a feature of sound by which a loud and a faint sound can be distinguished.
It depends upon the amplitude, surface area and distance from the vibrating body.
Sound energy flowing per second through unit area held perpendicular to the
direction of sound waves is called the intensity of sound. bel is unit of the intensity
level of sound, where 1 bel = 10 decibels
Pitch of the sound is the characteristics of sound by which a shrill sound can be
distinguished from a grave one. It depends upon the frequency.
The characteristics of sound by which two sound waves of same loudness and pitch
are distinguished from each other is called the quality of sound.
The sounds with jarring effect on our ears are called noise and the sounds having
pleasant effect on our ears are called musical sounds.
Noise pollution has become a major issue of concern in some big cities. Any form of
sound which disturbs the normal functioning of any natural ecosystem or some
human community is the cause of noise pollution.
Noise pollution can be reduced to acceptable level by replacing the rusty noisy
machinery with environment friendly machinery and equipments, putting sound reducing barriers, or using hearing protection devices.
The technique or method used to absorb undesirable sound energy by soft and
porous surfaces is called acoustic protection. This can be done by using soft, roug
11.2. What is the effect of the medium on the speed of sound? In which medium sound
travels more faster: air, solid or liquid? Justify your answer.
11.3. How can you prove the mechanical nature of sound by a simple experiment?
11.4. What do you understand by the longitudinal wave? Describe the longitudinal
nature of sound waves.
11.5. Sound is a form of wave. List at least three reasons to support the idea that sound is a wave.
11.6. We know that waves manifest phenomenon of reflection, refraction and
diffraction. Does sound also manifest these characteristics?
11.7. What is the difference between the loudness and intensity of sound? Derive the
relationship between the two.
11.8. On what factors does the loudness of sound depend?
11.9. What do you mean by the term intensity level of the sound? Name and define the
unit of intensity level of sound.
11.10. What are the units of loudness? Why do we use logarithmic scale to describe the
range of the sound intensities we hear?
11.11. What is difference between frequency and pitch? Describe their relationship
graphically.
11.12. Describe the effect of change in amplitude on loudness and the effect of change in
frequency on pitch of sound.
11.13. If the pitch of sound is increased, what are the changes in the following?
a. the frequency b. the wavelength
c. the wave velocity d. the amplitude of the wave
11.14. If we clap or speak in front of a building while standing at
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