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CBSE Questions for Class 8 Physics Sound Quiz 5 - MCQExams.com
CBSE
Class 8 Physics
Sound
Quiz 5
What all are the sources of noise pollution?
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Household sources like mixers, grinders, vacuum cleaners etc.
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Social events with loud speakers
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Transportation noises, traffic jams
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All of the above
Explanation
The presence of excessive or unwanted sounds in the environment is called noise pollution. Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers, television, and transistor radio at high volumes, some kitchen appliances, etc.
Water animals are also subjected to noise pollution.
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True
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False
Explanation
Yes. Water animals are affected by submarines and other vehicles which travel through the sea or ocean creating loud sound waves in water.
Which of the following voices is likely to have minimum frequency?
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Baby girl
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Baby boy
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A man
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A woman
Explanation
A man’s sound is of the lower pitch as compared to the other options. And we know that pitch is directly proportional to the frequency of sound. So, the frequency of man’s voice will be the minimum among all the options.
According to WHO (World Health Organisation), what is the loudness limit of sound in industries?
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$$50\ dB$$
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$$75\ dB$$
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$$100\ dB$$
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$$80\ dB$$
Explanation
The decibel scale is used to indicate levels of sound , that is , loudness or intensity of sound.
According to WHO. In industrial areas, the permissible limit is $$75$$ $$dB$$ for daytime and $$70$$ $$dB$$ at night to prevent noise pollution.
A hummingbird beats its wings $$ 3,300$$ times per minute. Find out the frequency produced by the bird?
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$$0.003\ Hz$$
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$$0.018\ Hz$$
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$$6\ Hz$$
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$$55\ Hz$$
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$$3300\ Hz$$
Explanation
Beat frequency is given by, number of beats per second,
in the given case ,
frequency-
$$ f = 3300\ \text{beats per minute}$$
$$\Rightarrow f = \dfrac{3300}{60}\ \text{beats per second}$$
$$\Rightarrow f = 55\ Hz$$
The property of ultrasonic waves used in manufacturing emulsion for photographic films is its ________.
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High speed
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High frequency
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Higher wavelength
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High amplitude
Explanation
Frequencies higher than $$20\ kHz$$ are called
ultrasonic sound or ultrasound.
The property of ultrasonic waves in manufacturing emulsion for photographic films in its high frequency.
Identify which of the following wave parameter is related to the
pitch of a sound?
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frequency
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amplitude
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wavelength
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period
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speed
Explanation
Pitch of a sound is more or less a proxy for frequency of sound, how quickly the sound wave is making the air vibrate. However f
requency is an objective, scientific attribute that can be measured. Pitch is each person's subjective perception o
f a sound wave, which cannot be directly measured.
Identify which of the following wave parameter is related to the volume of a sound?
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amplitude
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speed
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wavelength
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period
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frequency
Explanation
Intensity is perceived as the volume of a sound.
The amplitude of a wave is the measure of the intensity that it carries.
The more the amplitude, the more would be the intensity, and hence more would be the volume of the sound heard.
Elephants communicate with
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Sonic sound
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Infrasonic sound
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Ultrasonic sound
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None of these
Explanation
Elephants can communicate using very low frequency sounds, with pitches below the range of human hearing. These low frequency sounds(frequency less than $$20Hz$$), termed infrasonic sounds, can travel several kilometers, and provide elephants with a private communication channel that plays an important role in elephants complex social life. Their frequencies are as low as the lowest notes of a pipe organ.
A wave source produces $$10$$ oscillations in $$100\ ms$$. Find the time period of the wave.
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$$1\ s$$
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$$0.01\ s$$
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$$10\ s$$
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$$0.1\ s$$
Explanation
The number of oscillations per unit time is known as frequency $$f$$.
The time period $$T$$ is the time needed to complete one cycle or vibration.
$$f=\dfrac 1T$$
Given,
Number of oscillations, $$N = 10$$
Time, $$t=100\ ms$$
$$t= 100\times 10^{-3}=0.1\ s$$
Frequency, $$f= \dfrac Nt$$
$$f=\dfrac{10}{0.1}$$
$$f= 100\ Hz$$
Time period, $$T=\dfrac 1f$$
$$T=\dfrac{1}{100}
$$T=0.01\ s$
The audible range in humans is ____________.
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$$20 Hz$$ to $$2000 Hz$$
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$$200 Hz$$ to $$20,000 Hz$$
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$$20 Hz$$ to $$20,000 Hz$$
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$$200 Hz$$ to $$20 kHz$$
Explanation
Audible range of human ear is $$20Hz - 20000Hz$$
so the answer is C
Which one has higher frequency?
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Infrasonic sound
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Ultrasonic sound
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Audible sound
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All of the above have same frequency
Explanation
Audible sound has a frequency range of $$20 Hz$$ to $$20 \ kHz.$$
Infrasonic frequency is below audible range, i.e. below $$20 Hz$$.
Ultrasonic frequency is above audible range, i.e. above $$20KHz$$.
So the answer is B.
What is the unit for measuring the amplitude of a sound?
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decibel
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coulomb
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hum
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cycles
Explanation
The amplitude of sound is measured in decibel following the Bel System.
Noise is produced by
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Vibration with high frequency
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Regular vibration
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Regular and periodic vibration
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Irregular and non-periodic vibration
Explanation
Smooth and periodic vibration is music and irregular and non-periodic vibration is noise.
Which of the following is the vibrating part of Banjo?
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Stretched- Membrane
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Stretched- String
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Air column
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None of the above
Explanation
A Banjo is a string instrument. It gives a musical sound when plucked properly. The vibration of the string produces that sound.
Men sound on the ground at a fixed distance from a siren which emits the sound of fixed amplitude. The man hears the sound to be louder in a clear night than on a clear day.
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True
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False
Explanation
Usually, at the night, atmosphere is clean relative two days because of pollution other regular activities. When the fixed amplitude sound is produced with an instrument, the sound hear by the observer at a fixed distance will be different because pollution available in the atmosphere will absorb some of its energy.
But if the day is also clean as night then there will be no difference in the sound quality received by the observer.
Hence given statement is false.
When the pitch of note produced by a harmonium is lowered, then the wavelength of the note:
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decreases
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first decreases and then increases
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increases
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remains the same
Explanation
The shorter the wavelength, the higher the frequency, and the higher the pitch, of the sound.
Hence, pitch of harmonium is lowered so frequency will be lowered thus,
wavelength will be increased.
What is the approximate range of audible sound frequencies for a human with good hearing?
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From $$20Hz$$ to $$2000Hz$$
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From $$20Hz$$ to $$20000Hz$$
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From $$200Hz$$ to $$20000Hz$$
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From $$200Hz$$ to $$200000Hz$$
Explanation
Adult humans can hear from $$20Hz$$ to $$20000Hz$$ of frequency. Sound with frequency lower than $$20Hz$$ are called infrasonic, and higher than
$$20000Hz$$ are called ultrasonic or supersonic which are inaudible to humans.
Which one of the following is correct about the above statements?
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Statement 1 is true and 2 is false
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Statement 1 is false and 2 is true
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Both 1 and 2 are false
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Both a and 2 are true
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None of these
Explanation
Falling of leaves from the trees produces sound of very low decibel that doesn't come under pollution. Therefore, option (A) is correct and rest of the options is incorrect.
A particle vibrates 10 times in 1 sec. What is the time period of vibration of the particle?
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10 sec
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1 sec
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0.1 sec
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0.01 sec
Explanation
Time period of vibration is the time taken for 1 vibration.
Given:
10 vibrations are completed in $$1 \ sec.$$
So,
1 vibration will taken only: $$\dfrac{1}{10}=0.1 \ sec$$
The correct option is (C).
Which of the following statement best describes frequency?
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the maximum disturbance caused by a wave
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the number of complete vibrations per second
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the distance between one crest of a wave and the next one
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the distance travelled by a wave per second
Explanation
the number of complete vibrations per second
Write true or false for the following statements :
The audible range of frequencies is $$ 20\, Hz - 20 \, KHz $$ .
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True
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False
Explanation
Human ears can detect frequencies from $$ 20 \, Hz $$ to $$ 20\, KHz $$ only.
The unit of loudness of sound is decibel (db)
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True
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False
Explanation
Sound is measured in units called
decibels (dB
). The higher the decibel level, the louder the noise. On the decibel scale, the level increase of 10 means that a sound is actually 10 times more intense, or powerful.
Time taken to complete one vibration is called
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Frequency
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Time period
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Amplitude
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None of these
Explanation
Time taken to complete one vibration is called is called time period (T).
Sound corresponding to which frequency is ultrasonic sound?
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30 Hz
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300 Hz
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3000 Hz
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30,000 Hz
Explanation
30,000 Hz
Sound having a frequency of more than 20000 Hz in known as ultrasonic. It can not heard by us.
When we change feeble sound to loud sound we increase its :
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frequency
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amplitude
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velocity
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wavelength
Explanation
The amplitude is the measure of loudness of a sound. When our music system is having a feeble sound by increasing the amplitude, the sound now becomes louder.
The loudness of sound is determined by the
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amplitude of vibration
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ratio of amplitude and frequency of vibration
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frequency of vibration
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product of amplitude and frequency of vibration
Explanation
The amplitude of sound determines the loudness of sound. A sound that is faint will have a small amplitude while that of a loud sound will have larger amplitude.
In the bell jar experiment, as air is removed from the jar :
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intensity of sound falls
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speed of sound falls
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intensity of sound increase
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speed of sound increases.
Explanation
Sound is a mechanical wave and needs a material medium like air, water, steel, etc. for its propagation. As the air is pumped out of the sealed bell jar, the sound from the bell jar fades, because the medium is being removed, thus the intensity of sound decreases.
1 hertz is equal to
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1 vibration per minute
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10 vibrations per minute
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60 vibrations per minute
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600 vibrations per minute
Explanation
Hertz is the unit of frequency.
$$1\ Hz = 1\ vibration\ per\ sec = 60\ vibrations\ per\ minute$$
A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case
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sound will be louder but pitch will not be different
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sound will be louder and pitch will also be higher
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sound will be louder but pitch will be lower
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both loudness and pitch will remain unaffected
Explanation
Any sound wave pitch depends on the frequency of the wave. When the mechanical piano is struck harder the second time, we find
sound will be louder but pitch remains the same because the frequency has not changed.
The pitch depends on frequency of the particular key which is being hit and hence there would be no change in pitch of sound. Loudness depends on amplitude which will be more if key is struck harder.
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