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.
🙁 d) Sound can travel through solids, liquids, and
gases.
2) Which of the following voices is likely to have minimum
frequency?
frequency?
(a) Baby girl (b) Baby boy
(c) A man (d) A woman
ANSWER:
– A man
– A man
3) In the following
statements, tick ‘T’ against those which are true, and ‘F’ against those which
are false.
statements, tick ‘T’ against those which are true, and ‘F’ against those which
are false.
(a) Sound cannot
travel in vacuum. (T / F)
travel in vacuum. (T / F)
(b) The number of
oscillations per second of a vibrating object is called its time period. (T /
F)
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)
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)
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)
frequency of vibration, the higher is the pitch. (T / F)
(f) Unwanted or
unpleasant sound is termed as music. (T / F)
unpleasant sound is termed as music. (T / F)
(g) Noise pollution
may cause partial hearing impairment. (T/F)
may cause partial hearing impairment. (T/F)
ANSWER:-
a)True
b) False
c) False
d)True
e) False
f) False
g)True
4) Fill in the blanks with suitable words.
(a) Time taken by an object to
complete one oscillation is called __time period__.
complete one oscillation is called __time period__.
(b) Loudness is determined by the
__amplitude__ of vibration.
__amplitude__ of vibration.
(c) The unit of frequency is __hertz
(Hz) __.
(Hz) __.
(d) Unwanted sound is called
__noise__.
__noise__.
(e) Shrillness of a sound is
determined by the __frequency__ of vibration.
determined by the __frequency__ of vibration.
5) A pendulum
oscillates 40 times in 4 seconds. Find its time period and frequency.
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
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.
period. It is given by the inverse of the frequency.
Time period = 1/ (Frequency of Oscillation) = 1/10 = 0.1 sec.
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?
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 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 Oscillation)
Frequency of
oscillations = 500 Hz
oscillations = 500 Hz
Time period =
1/500 = .002 s
1/500 = .002 s
7) Identify the
part which vibrates to produce sound in the following instruments. (a) Dholak
(b) Sitar (c) Flute
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.
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.
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.
air inside the pipe is set into vibration.
As a result, a pleasant sound is produced.
8) What is the difference
between noise and music? Can music become noise sometimes?
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, pangs, etc. The sound
that is unpleasing to the ear is called noise
example, the sound produced by violins, pianos, flutes, pangs, etc. The sound
that is unpleasing to the ear is called noise
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
running at high volumes
(ii) Loudspeakers and crackers
(iii) Horns of buses, cars and trucks
(iv) Home appliances such as mixer,desert cooler, etc.
10) Explain in what
way noise pollution is harmful to humans.
way noise pollution is harmful to humans.
ANSWER:-Noise pollution can lead to a number of health-related problems
like Hearing loss, insomnia, stress etc.
like Hearing loss, insomnia, stress etc.
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.
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
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
12) Sketch larynx
and explain its function in your own words.
and explain its function in your own words.
ANSWER:-
Larynx moves when we swallow something. Inside the larynx, there
are two vocal cords.
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.
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.