Question 1: Choose the
correct answer. Sound can travel through
(a) gases only (b) solids only (c) liquids only (d) solids,
liquids and gases.
Answer:
(d) Sound can travel through solids, liquids, and gases.
Sound requires a medium to travel through. Solid, liquid and gas provide the
medium for sound. Hence, sound can travel through solids, liquids and gases.
Question 2: Which of
the following voices is likely to have minimum frequency?
(a) Baby girl (b) Baby boy (c) A man (d) A woman
Answer:
(c) A man The voice of an adult man is of lower pitch in
comparison to the voices of a baby boy, a baby girl and a woman. Since
frequency of a sound is directly proportional to its pitch, man’s voice is of
minimum frequency in comparison to a boy, a girl, or awoman’s voice.
Question 3: In the
following statements, tick ‘T’ against those which are true, and ‘F’ against
those which are false.
(a) Sound cannot travel in vacuum. (T / F)
(b) The number of oscillations per second of a vibrating
object is called its time period. (T / F)
(c) If the amplitude of vibration is large, sound is feeble.
(T / F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz.
(T / F)
(e) The lower the frequency of vibration, the higher is the
pitch. (T / F)
(f) Unwanted or unpleasant sound is termed as music. (T / F)
(g) Noise pollution may cause partial hearing impairment.
(T/F)
Answer:
(a) True Sound requires a medium to travel through. Since
vacuum is devoid of any medium, sound cannot travel through it.
(b) False The number of oscillations per second of a
vibrating object is known as its frequency. Time period is the time required to
complete one oscillation.
(c) False Loudness of a sound is proportional to the square
of the amplitude of its vibration. When the amplitude of vibration of a sound
is large, the sound is very loud. The sound is feeble for small amplitude.
(d) True Humans cannot hear sounds of all frequencies. Humans
can hear a sound whose frequency falls in the range of 20 Hz−20,000 Hz. The
sound having frequency out of this range is inaudible to humans.
(e) False The pitch of a sound is proportional to its
frequency. As the frequency of vibration increases, the pitch of the sound also
increases and vice-versa. A sound is said to be high pitched if its frequency
of vibration is high, and is low pitched for a small frequency of vibration.
(f) False Unwanted or unpleasant sounds are known as noise. Sounds that are
melodious and pleasing to ear are known as music.
(g) True Unwanted or unpleasant sounds are known as noise. If
one is subjected to loud unpleasant sound continuously for a long time, then it
may cause temporary hearing impairment.
Question 4: Fill in the
blanks with suitable words.
(a) Time taken by an object to complete one oscillation is
called _________.
(b) Loudness is determined by the ________ of vibration.
(c) The unit of frequency is _________.
(d) Unwanted sound is called _________.
(e) Shrillness of a sound is determined by the _________ of
vibration.
Answer: (a) Time
taken by an object to complete one oscillation is called __time period__.
(b) Loudness is determined by the __amplitude__ of vibration.
(c) The unit of frequency is __hertz (Hz) __.
(d) Unwanted sound is called __noise__.
(e) Shrillness of a sound is determined by the __frequency__
of vibration. (Shrillness is also called pitch of the sound. Pitch is directly
proportional to the frequency of vibration. Hence, shrillness is determined by
the frequency of vibration.)
Question 5: A pendulum
oscillates 40 times in 4 seconds. Find its time period and frequency. Answer:
Frequency of oscillations is defined as the number of
oscillations of a vibrating body per second. It is given by Frequency = (Number
of Oscillations)/Time = 40/4 = 10 Hz The time required to complete one
oscillation is known as time period. It is given by the inverse of the
frequency. Time period = 1/(Frequency of Oscillation) = 1/10 = 0.1 sec.
Question 6: The sound
from a mosquito is produced when it vibrates its wings at an average rate of
500 vibrations per second. What is the time period of the vibration?
Answer: The time
required to complete one oscillation is known as time period. It is given by
the inverse of the frequency. Time period = 1/(Frequency of Oscillation)
Frequency of oscillations = 500 Hz Time period = 1/500 = .002 s
Question 7: Identify
the part which vibrates to produce sound in the following instruments. (a)
Dholak (b) Sitar (c) Flute
Answer:
(a) Dholak is a musical instrument. It consists of a
stretched membrane called its head. When the head is beaten gently, the stretched
membrane sets into vibration. Since sound is produced when an object vibrates,
the dholak produces a sound.
(b) Sitar is a musical instrument. It consists of stretched
strings. When a string is plucked, it sets into vibration. Since sound is
produced when an object vibrates, the sitar produces a sound.
(c) Flute is a hollow pipe. When air is blown over its mouth,
the air inside the pipe is set into vibration. As a result, a pleasant sound is
produced.
Question 8: What is the
difference between noise and music? Can music become noise sometimes?
Answer: The sound that is pleasing to the ear is
called music. For example, the sound produced by violins, pianos, flutes,
pungs, etc. The sound that is unpleasing to the ear is called noise. Some
examples of noise are as follows:
(i) Sound produced by horns of buses and trucks
(ii) Sound of electrical generators
(iii) Sound of a gun shot
(iv) Sound produced by jackhammers Yes. Music can become
noise when played at high volumes.
Question 9: List
sources of noise pollution in your surroundings.
Answer: Some
sources of noise pollution are as follows:
(i) Televisions and transistors running at high volumes
(ii) Loudspeakers and crackers
(iii) Horns of buses, cars and trucks
(iv) Home appliances such as mixer, desert cooler, etc.
Question 10: Explain in
what way noise pollution is harmful to humans.
Answer: Noise
pollution can lead to a number of health-related problems. Some of them are as
follows: (i) Hearing loss (ii) Insomnia; inability to sleep (iii) Hypertension
(iv) Severe headache (v) Stress
Question 11: Your
parents are going to buy a house. They have been offered one on the roadside
and another three lanes away from the roadside. Which house would you suggest
your parents should buy? Explain your answer.
Answer: There will
be more noise in the house which is along the roadside. This is because noise
produced by transportation vehicles may cause trouble to the residents. The
intensity of noise decreases with the distance between the source and the
listener. Hence, it is better to take the house that is three lanes away from
the roadside.
Question 12: Sketch
larynx and explain its function in your own words.
Answer: Larynx is a
part of the throat. It is responsible for production of sound. A sketch of a
human larynx is shown in the following figure.
Larynx moves when we swallow something. Inside the larynx,
there are two vocal cords. There is a small gap between them. This small gap
allows air to pass through. When we speak, air is forced into this small gap by
the lungs. This prompts vocal cords to vibrate. Since vibrating objects produce
sound, sound is produced due to the vibration of vocal cords.
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