Students can Download Science Chapter 12 Sound Questions and Answers, Notes Pdf, KSEEB Solutions for Class 9 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.
Karnataka State Syllabus Class 9 Science Chapter 12 Sound
KSEEB Class 9 Science Sound Intext Questions and Answers
Question 1.
How does the sound produced by a vibrating object in a medium reach your ear?
Answer :
Particles set in motion starts vibrating the particles of a medium. In displacing the adjacent particles, the particles possess kinetic energy transfers its energy of disturbance reaches the ear.
Question 2.
Explain how sound is produced by your school bell.
Answer :
The disturbance of a bell with rod vibration causes to transfer (air particles I do not travel) they oscillate and transfer the disturbance.
Question 3.
Why are sound waves called mechanical waves?
Answer :
Sound requires a material medium for its propagation and disturbance is carried forward.
Question 4.
Suppose you and your friend are on the moon will you be able to hear any sound produced by your friend?
Answer :
No atmosphere on the moon (vacuum) sound cannot travel through a vacuum, sound required medium for its propagation.
Question 5.
Which wave property determines
(a) loudness
(b) pitch?
Answer :
(a) Loudness: Amplitude
(b) Pitch: Frequency
Question 6.
Guess which sound has a higher pitch guitar or car horn?
Answer :
Car horn due to higher-order pitch.
Question 7.
What are the wavelength, frequency, time period, and amplitude of a sound wave?
Answer :
- Wavelength: Distance between two consecutive compressions or rarefactions, denoted by 1, unit is meter,
- Frequency: Number of oscillations per I unit time, it’s unit is Hertz (Hz) denoted 1 by T.
- Time period: Time taken for the wave (disturbance of compressions and rarefactions) denoted by T, the unit is second.
- Amplitude: the magnitude of maximum displacement in the medium from the mean position.
Question 8.
How are the wavelength and frequency of a sound wave related to its speed?
Answer :
Speed = wavelength x frequency
Question 9.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Answer :
Question 10.
A passion is listening to a tone of 500 Hz sitting at a distance of 450 M from the source of the sound. What is the time interval between successive compression from the source?
Answer :
V = \(\frac{1}{\mathrm{T}}\)
T = \(\frac{1}{\mathrm{V}}\) = \(\frac{1}{\mathrm{500}}\) = 0.002 second
Question 11.
Distinguish between loudness and intensity of sound.
Answer :
| Loudness | Intensity |
| The measure of the response of the ear to the sound. | Amount of sound energy passing each second per unit area. |
| It depends upon the sensitivity of the ear. | It is a physical quality and magnitude does not depend on the sensitivity of the ear. |
Question 12.
In which of the three media air-water or iron? Does sound travel the fastest at a particular temperature?
Answer :
Iron
Question 13.
An echo was heard after 3 s what is the distance of the reflecting surface from the source given that the speed of sound in 342 ms-1?
Answer :
Distance = 342 x 3 = 1026 M
∴ Distance from reflecting surface
= \(\frac{1026}{2}\) = 512 M
Question 14.
Why are the ceilings of concert halls curved?
Answer :
To prevent reflection of sound, and which can speed evenly across the width of the hall.
Question 15.
What is the audible range of the average human ear?
Answer :
20 Hz to 20.000 Hz
Question 16.
What is the range of frequencies associated with water
(a) infrasound (b) ultrasound.
Answer :
(a) Infrasound: Less than 20 Hz
(b) Ultrasound: More than 20.000 Hz
Question 17.
A submarine emits a sonar pulse which returns from an underwater cliff is 1.02 s if the speed of sound in saltwater is 1531 m/s. How far away is the cliff?
Answer :
\(\begin{aligned}
\mathrm{d} &=\frac{\mathrm{V} \times \mathrm{t}}{2}=\frac{1531 \times 1 \cdot 02}{2} \\
&=1531 \times 0.51
\end{aligned}\)
KSEEB Class 9 Science Sound Textbook Exercise Questions and Answers
Question 1.
What is sound and how is it produced?
Answer :
Form of energy, produced by the vibration of particles in a matter.
Question 2.
Describe with the help of a diagram, how compressions and rarefactions arc produced ¡n air near a source of the sound.
Answer :
Fig. Sound propagates as density or pressure variations as shown in (a) and (h), (c) represents graphically the density and pressure variations.
Question 3.
Cite an experiment to show that sound needs a material medium for its propagation.
Answer :
Fig. Bejar experiment showing sound cannot travel in a vacuum.
Question 4.
Why is a sound wave called a longitudinal wave?
Answer :
(a) Produces compressions and rare ‘ factions
(b) Require material medium for its propagation.
Question 5.
Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer :
Frequency
Question 6.
Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Answer :
Flash (light) velocity is more than that of thunder (sound)
Question 7.
A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound m air as 344 ms1.
Answer :
V = λ
V = f λ
344 = 20 x λ 344 = 2000 x λ
\(\frac{344}{20}=\lambda\)
\(\lambda=\frac{344}{20000}\)
17 m = λ
λ = 0.017 M
Question 8.
Two children are at opposite ends of an aluminum. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in the air and in aluminum to reach the second child.
Answer :
V1 = 346 m/s
V2 = 6240 m/s
Length of aluminium rod = x m
Time taken in aluminium = \(\frac{x}{6420}\) sec Required ratio
Question 9.
The frequency of a source of sound is 100 IIz. How many times does it vibrate in a minute?
Answer :
Frequency = 100 + 12
Time taken = 1 mm = 60 sec
Frequency \(\frac{\text { Number of oscillations }}{\text { Time taken }}\)
Number of oscillations
= v x t = 100 x 60 = 6000 times
Question 10.
Does sound follow the same laws of reflection as light docs? How
Answer :
Yes. The angle of incidence and angle of reflection obeys the laws.
Question 11.
When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?
Answer :
Yes. The molecular distance is more ‘frequently carries the energy due to high temperature.
Question 12.
Give two practical applications of reflection of sound waves.
Answer :
- Working of sonar
- Mechanism of echo
Question 13.
A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 19 m s-2 and speed of sound = 340 m s-1.
Answer :
(a) Distance = 500 m
u = 0, a = 10 m/s2
s = ut +\(\frac{1}{2}\) gt2
500 = (0xt) + \(\frac{1}{2}\) x 10 x t2
t = 10sec
(b) Speed = 340 m/s
500 = \(\frac{500}{340}\) = 1.47
Total = 10 + 1.47 = 11.47 sec
Question 14.
A sound wave travels at a speed of 339 in s-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Answer :
V = f x λ
\(\frac{3390}{15}\) = f
339 = f x 0.015
226 Hz = f
\(\frac{339}{0 \cdot 05}=\mathrm{f}\) Audible sound
= 22600 H2
Question 15.
What is reverberation? How can it be reduced?
Answer :
Persistence of sound in an auditorium results in repeated reflections called reverberation. Designing the building and the distance to be maintained more than 17 m.
Question 16.
What is the loudness of sound? What factors does it depend on?
Answer :
It is a physiological response of the ear to the intensity of the sound. Dependable factors an :
- Amplitude
- frequency
Question 17.
Explain: how bats use ultrasound to catch prey.
Answer :
Echoranging determines the time period with the corresponding velocity of the ultrasonic sound. Gives us the distance.
\(d=\frac{v \times t}{2}\)
Question 18.
How is ultrasound used for cleaning?
Answer :
(a) Inertia and frequency.
(b) Provided energy from the ultrasonic sound.
Readily oscillate and vibrate to detach from the surface.
Question 19.
Explain the working and application of a sonar.
Answer :
Working: SONAR stands for Sound Navigation and Ranging.
It consists of transmitter and detector, transmitter transmit electrical signal into ultrasonic sound signal and detector converts ultrasonic sound into an electrical signal.
‘d’ is the total distance, t – total time is taken, v – velocity of the ultrasonic sound waves.
Depth = \(\frac{V \times t}{2}\)
Applications:
- The depth of the ocean can be determined.
- Location of submarines.
Question 20.
A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.
Answer :
Question 21.
Explain how defects in a metal block can be detected using ultrasound.
Answer :
Transmitter and receiver both works on echo ranging.
Metalic components are generally used 14 construction of big structures, defects of metal plates (cracks and holes) are generally infusible from outside reduces the strength of the structures, ultrasonic sounds are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is small defect, the ultrasound gets reflected back indicating the presence of feat or defect.
Fig. Ultrasound is reflected back from the defective locations inside a metal block.
Question 22.
Explain how the human ear works.
Answer :
Fig. An auditory part of the human ear Outer ear pinna collects the sound from the surroundings and passes into the auditory canal. Leads to the eardrum or tympanic membrane the compressions and rarefactions reach it and eardrum vibrates, graph bed several times by three bones (hammer anvil and stir rap) in the middle ear. Pressure vibrations are received the inner ear turned to electrical are sent to the brain via the auditory nerve and the brain interprets them as sound.
KSEEB Class 9 Science Sound Additional Questions and Answers
Answer the following questions:
Question 1.
State the laws of reflection of sound.
Answer :
(i) The angle of incidence is equal to the angle of reflection of sound in a medium.
(ii) The direction of the incident sound, the direction of reflection of sound, and the normal to the point of incidence all He in the same plane.
Question 2.
Why we cannot hear an echo in a small room?
Answer :
The distance between the opposite walls is less than 17 m. Hence we cannot hear an echo in a small room.
Question 3.
Name the physical quantity which determines the loudness of sound?
Answer :
The amplitude of the vibrating body.
Question 4.
Define reverberation time?
Answer :
The time interval during which the original sound appears to prolong.
Question 5.
What type of waves are produced by bats?
Answer :
Ultrasonic waves.