Question: 1 - How does the sound produced by a vibrating object in a medium
reach your ear?
Answer:- Vibrations in an object create disturbance in the medium and
consequently compressions and rarefactions. Because of these compressions and
rarefactions sound reaches to our ear.
Question: 1 - Explain how sound is produced by your school bell.
Answer:- School bell starts vibrating when heated which creates
compression and rarefaction in air and sound is produced.
Question: 2 - Why are sound waves called mechanical waves?
Answer: Since sound waves do some mechanical work while making
disturbance in medium, hence sound waves are called mechanical wave.
Question: 3 -Suppose you and your friend are on the moon. Will you be able to
hear any sound produced by your friend?
Answer: Since sound waves require medium to propagate and there is no
medium present on the moon. So, I will not able to hear the sound of my friend
on the moon.
Question: 1 - Question: 1 - Which wave property determines (a) loudness, (b)
pitch?
Answer: (a) Amplitude of sound waves determines loudness. Louder sound
has greater amplitude and vice versa.
(b)
Frequency of the sound waves determined pitch of the sound.
Question: 2 - Guess which sound has a higher pitch: guitar or car horn?
Answer: Sound of the car horn has higher pitch.
Question: 3 - What are wavelength, frequency, time period and amplitude of a
sound wave?
Answer: Wavelength: Wavelength is the distance between two consecutive compressions
or rarefaction of wave.
Frequency:
The number of sound wave produced in one second is called frequency.
Time
period: Time period is the time taken to produce one wave of sound.
Amplitude:
Amplitude is the maximum displacement along the mean position of the particles
of medium.
Question: 4 - How are the wavelength and frequency of a sound wave related to
its speed?
Answer: The relation between frequency and wavelength of sound wave is
given as follows:
Velocity
(v)=Wavelength(λ)X Frequency (ν), v = λX ν
This
means the speed is equal to the product of wavelength and frequency of the
sound wave.
This
equation is also called the ‘wave equation’ and applicable to all types of
wave.
Question: 5 - Calculate the wavelength of a sound wave whose frequency is 220
Hz and speed is 440 m/s in a given medium.
Answer:
Given,
Frequency
(ν) = 220 Hz
Velocity
(v) = 440m/s
Wavelength
(λ) =?
Thus,
wavelenght = 2m
Question: 6 - A person 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 compressions from the source?
Answer: Since,
the time interval between successive compressions is called time period or time
interval.
Here
given,
Frequency
(ν) = 500Hz
T
(Time period) =?
Thus,
time interval between two consecutive compression of the given wave = 0.2 s
Question: 7 - Distinguish between loudness and intensity of sound.
Answer: Loudness
of sound is determined of amplitude and intensity of the sound wave is determined
by frequency of sound waves.
Question: 1 - In which of the three media; air, water or iron does the sound
travel the fastest at a particular temperature?
Answer:At
particular temperature sound travels fastest in iron.
Question: 1 - An echo returned in 3 s. What is the distance of the reflecting
surface from the source, given that the speed of sound is 342 m /s?
Answer:To
return an echo sound has to cover distance of two way.
Here,
given,
Speed
of sound = 342 m/s
Time
= 3s
Thus,
Distance
= speed X time
⇒
Distance = 342m/s×3 s=1026 m
Thus,the
distance between the source and reflecting surface=1026÷2=513m
Question: 1 -Why are the ceilings of concert halls curved?
Answer: Since,
concert halls are big, so audience at the back rows of the hall may not hear
clear sound of speaker. To overcome this problem, the ceiling of the concert
halls is made concave. Concave ceiling helps the sound wave to reflect and send
to farther distance which makes the concert hall enable to send clear sound to
the audience even sitting in back rows of hall.
Question: 1 - What is the audible range of the average human ear?
Answer: 20
Hz to 20000 Hz
Question: 2 - What is the range of frequencies associated with
(a)
Infrasound
(b)
Ultrasound
Answer:
(a)
Infrasound: Less than 20 Hz
(b)
Ultrasound: More than 20000 Hz
Question: 1 - A submarine emits a SONAR pulse, which returns from an
underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s,
how far away is the cliff ?
Answer:To
return the SONAR pulse back, its wave has to travel two way.
Here,
given,
Velocity
(v) of sound wave = 1531m/s
Time
(T) = 1.02 s
Thus,
Distance = speed X time
Distance=1531
ms^(-1)×1.02 s=1561.62 m
So,the
distance between the source and reflecting surface=1561.62÷2=780.81m
Exemplar Problems (NCERT) and Solutions
Multiple Choice Questions
Question: 1 -Note is a sound
(a) of mixture of several frequencies
(b) of mixture of two frequencies only
(c) of a single frequency
(d) always unpleasant to listen
Answer: (a) of mixture of several
frequencies
Question:- 2 - A key of a mechanical
piano struck gently and then struck again but much harder this time. In the
second case
(a) sound will be louder but pitch will not be different
(b) sound will be louder and pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected
Answer:- (d) both loudness and
pitch will remain unaffected
Question: 3 - In SONAR, we use
(a) ultrasonic waves
(b) infrasonic waves
(c) radio waves
(d) audible sound waves
Answer: (a) Ultrasonic waves
Question:- 4 - Sound travels in air if
(a) particles of medium travel from one place to another
(b) there is no moisture in the atmosphere
(c) disturbance moves
(d) both particles as well as disturbance travel from one place to
another.
Answer:- (c) Disturbance moves
Question: 5 - When we change feeble
sound to loud sound we increase its
(a) Frequency
(b) Amplitude
(c) Velocity
(d) Wavelength
Answer: (b) Amplitude
Question: 6 - In the curve (Figure)
half the wavelength is
(a) A B
(b) B D
(c) D E
(d) A E
Answer: (a) AB
Question: 7 - Earthquake produces
which kind of sound before the main shock wave begins
(a) Ultrasound
(b) Infrasound
(c) audible sound
(d) none of the above
Answer: (b) Infrasound
Question: 8 - Infrasound can be heard
by
(a) Dog
(b) Bat
(c) Rhinoceros
(d) human beings
Answer: (c) Rhinoceros
Question: 9 - Before playing the
orchestra in a musical concert, a sitarist tries to adjust the tension and
pluck the string suitably. By doing so, he is adjusting
(a) intensity of sound only
(b) amplitude of sound only
(c) frequency of the sitar string with the frequency of other
musical instruments
(d) loudness of sound
Answer: (c) Frequency of the sitar
string with the frequency of other musical instruments
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