Q 1 – The voice box is also called as
(a) stomach
(b) heart
(c) larynx
(d) mouth
Ans. (c) larynx
Q 2 – Pitch of sound is determined by its
(a) frequency
(b) speed
(c) amplitude
(d) loudness
Ans. (a) frequency
Q 3 – Cochlea is a part of
(a) hearing organ
(b) sound producing organ
(c) muscular organ
(d) air pollution
Ans. (a) hearing organ
Q 4 – Speed is
(c) Distance travelled × Time
(d) Time + Distance travelled
Ans. (a)
Q 5 – The number of vibrations made by a vibrating body in one second is
(a) frequency
(b) noise
(c) loudness
(d) pitch
Ans. (a) frequency
Q 6 – Sound is produced by
(a) Non-Vibrating objects only
(b) Vibrating and non- vibrating objects
(c) Vibration has no relation to sound
(d) Vibrating objects only
Ans. (d) Vibrating objects only
Q 7 – Frequency is expressed in
(a) Kilometer
(b) Hertz
(c) gram
(d) Degree centigrade
Ans. (b) Hertz
Q 8 – Above _____ dB the sound becomes physically painful
(a) 60
(b) 40
(c) 120
(d) 80
Ans. (d) 80
Q 9 – An ultrasound equipment works at frequency
(a) Higher than 20,000 Hz
(b) Higher than 10,000 Hz
(c) Lower than 20,000 Hz
(d) Lower than 10,000 Hz
Ans. (a) Higher than 20,000 Hz
Q 10 – Voice of man is heavy compared to a woman because
(a) Female vocal cord is longer
(b) Male vocal cord is shorter
(c) Male vocal cord is longer
(d) The concept is not related
Ans. (c) Male vocal cord is longer
Q 11 – Vibration is also known as
(a) Vibratory motion
(b) Translatory motion
(c) Oscillatory motion
(d) None of these
Ans. (c) Oscillatory motion
Q 12 – The voice box is also called as
(a) stomach
(b) heart
(c) larynx
(d) mouth
Ans. (c) larynx
Q 13 – 1 hertz is equal to
(a) 1 vibration per minute
(b) 10 vibrations per minute
(c) 60 vibrations per minute
(d) 600 vibrations per minute
Ans. (c) 60 vibrations per minute
Q 14 – Sound travels through ____ ?
a) Water only
b) Vacuum
c) Liquid , gas & solid
Ans. c) Liquid , gas & solid
Q 15 – Above _____ db the noise becomes physically painful ?
a) 70
b) 80
c) 60
Ans. b) 80
Q 16 – Impairment of hearing is caused by ____ pollution ?
a) Air
b) Noise
Ans. b) Noise
Q 17 – The number of oscillations per second is called ______ of oscillation ?
a) Frequency
b) Amplitude
Ans. a) Frequency
Q 18 – _____ sends vibrations to the inner ear ?
a) Larynx
b) Eardrum
Ans. b) Eardrum
Q 19 – Sonali heard sound of thunderbolt 5 second after she saw flash of lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s)
Ans. Distance of Sonali from the place of lightning = 330 × 5 = 1650 m
Q 20 – What do you mean by oscillatory motion?
Ans. The to and fro motion of an object is called vibration. This motion in both the direction from its mean position is called oscillatory motion.
Q 21 – What do you mean by time period?
Ans. The time taken by a vibrating body to complete one oscillation is called the time period.
Q 22 – What is the relation between ‘time-period’ and ‘frequency’ of an oscillating
body?
Ans. Time Period given by the inverse of the frequency.
Time Period = 1/frequency
Q 23 – Name one solid, one liquid and one gas through which sound can travel.
Ans. Solid: Metal (Iron, Steel, Aluminium), wood, bricks etc.
Liquid: Water
Gas: Air
Q 24 – State the differences between ultrasonic sound and infrasonic sound?
Ans.
| Ultrasonic sound | Infrasonic sound |
| (i) Sound of frequency higher than 20,000 Hz is called ultrasonic sound. | (i) Sound of frequency lower than 20 Hz is called the infrasonic sound. |
| (ii) Animals like dog, bat, monkey, deer, etc., can hear ultrasonic sound. | (ii) Animals like whale, elephant, hippopotamus, giraffe, etc., can hear infrasonic sound. |
Q 25 – Differentiate between musical sound and noise.
Ans.
| Musical sound | Noise |
| (i) Musical sound is pleasant, smooth and agreeable to the ear. | (i) Noise is unpleasant, jarring and disagreeable to the ear. |
| (ii) It is produced by periodic vibrations which are regular and continuous. | (ii) It is produced by irregular vibrations which are discontinuous. |
| (iii) There are no sudden changes in loudness and pitch of musical sound. | (iii) There are sudden changes in loudness and pitch of noise. |
Q 26 – What are the methods to control noise pollution?
Ans. Following are the methods to control noise pollution:
- The noise pollution can be controlled by reducing the respective sources of noise pollution.
- The blowing of horns and speaker should be strictly avoided near schools and hospitals.
- More and more trees should be planted on roadside because trees absorb sound.
Q 27 – Define frequency.
Ans. The number of oscillations completed by a vibrating body in one second is called frequency. The unit of frequency is hertz. It is denoted by Hz. If a vibrating body makes 20 oscillations in a second we say that its frequency is 20 Hz. The human voice can produce frequency between 60 Hz and 13,000 Hz. It is interesting that a human ear can hear sound of frequency between 20 Hz to 20,000 Hz.
Q 28 – How is sound produced and how is it transmitted and heard by us?
Ans. Sound is a form of energy produced and transmitted by a vibrating matter. It travels in form of waves through matter and moves in to and fro direction. When this wave reach eardrum it makes the eardrum to vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we are able to hear the sound.
Q 29 – On Ramesh’s 13th birthday, his father invited all his friends and their relatives. It was a big party with lots of food and DJs. Ramesh didn’t like the loud sound of DJs and asked his father to play it in a low volume so that their neighbours do not get much disturbed and people in the party can also enjoy the music. Ramesh’s father felt good for his wisdom and did as he said.
- Do you enjoy loud sound DJs in parties?
- Do you think when loud music is played in a party is acceptable to all the people living in , neighbourhood?
- How can you control noise pollution at your end?
- What value of Ramesh is shown here?
Ans.Yes/No (according to your choice)
No, it may be not acceptable to all the people living in neighbourhood.
We can control noise pollution at our end by:
- not playing music loudly.
- planting trees around house.
- cushioning gaps in windows and doors.
- using ear plugs at noisy places.
- doing meditation.
Ramesh is wise, mature, knows hazards of noise pollution, concern about others and good-hearted.
Q 30 – Prepare a list of famous Indian musicians and the instruments they play.
Ans. (a) Ustad Amjad Ali Khan – Sarod
(b) Bismillah Khan – Sehnai
(c) Hariprasad Chaurasia – Flute
(d) Zakir Hussain – Tabla
(e) Ravi Shankar – Sitar
Q 31 – Make two toy telephones. Use them as shown in Fig. 13.14. Make sure that the two strings are taut and touch each other. Let one of you speak. Can the remaining three persons hear? See how many more friends you can engage in this way. Explain your observations.
Ans.
Yes, remaining three persons can hear because sound can travel through string.
Q 32 – What are called inaudible sounds?
Ans. The fact is that sounds of frequencies less than about 20 vibrations per second (20 Hz) and higher than about 20,000 vibrations per second (20000 Hz) cannot be detected by the human ear. Such sounds are called inaudible sounds.
Q 33 – 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?
Ans. Time period = 1/(Frequency of Oscillation)
Frequency of oscillations = 500 Hz
Time period = 1/500 = .002 s
Q 34 – Write the loudness of the following in decibels:
Normal breathing, Soft whisper (at 5m), Normal conversation, Busy traffic and Average
factory
Ans.
Normal breathing – 10 dB
Soft whisper (at 5m) – 30 dB
Normal conversation – 60 dB
Busy traffic – 70 dB
Average factory – 80 dB
Q 35 – Identify the part which vibrates to produce sound in the following
instruments: (a) Dholak (b) Sitar (c) Flute (d) Cymbals (e) Veena (f) Tabla
Ans.
Dholak – stretched membrane
Sitar – strings
Flute – air columns
Cymbals – metal plates
Veena – strings
Tabla – stretched membrane
Q 36 – List sources of noise pollution in your surroundings
Ans. Some sources of noise pollution are as follows:
- Running of mixer and grinder
- Blowing of horns of motor vehicles
- Bursting of crackers
- Taking off and landing of aeroplanes
- Sounds of loudspeakers
- High volumes in televisions and transistors
Q 37 – What is the difference between noise and music? Can music become noise sometimes?
Ans. Noise: The unpleasant sounds around us are called noise.
Example:
- Running of mixer and grinder
- Blowing of horns of vehicles
- Bursting of crackers
Music: The sounds which are pleasant to hear are called music
Example: Sounds from musical instruments such as harmonium, sitar, guitar, flute etc.
If a musical sound becomes too loud, it would become noise.
Q 38 – Sketch larynx and explain its function in your own words.
Or
Describe how sound is produced by the human voice box (or larynx)
Ans. In humans, the sound is produced by the voice box or the larynx. It is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the slit, the vocal cords vibrate, producing sound.
Q 39 – State the various measures which can be taken to control noise pollution in our surroundings.
Ans. Measures to limit noise pollution
- Silencing devices must be installed in air craft engines, transport vehicles, industrial
machines and home appliances. - Use of automobile horns should be minimised.
- The noisy operations must be conducted away from any residential area.
- Noise producing industries should be set up away from such areas.
- TV and music systems should be run at low volumes.
Q 40 – How can you show that sound cannot travel through a vacuum?
Ans. Take a metal glass tumbler. Place a cell phone in it. Ask your friend to give a ring on this cell phone from another cell phone. Listen to the ring carefully. Now, surround the rim of the tumbler with your hands. Put your mouth on the opening between your hands.
Indicate to your friend to give a ring again. Listen to the ring while sucking air from the tumbler. You will observe that the sound become fainter as you suck. If you had been able to suck all the air in the tumbler, the sound would stop completely. Actually, sound needs a medium to travel. When air has been removed completely from a vessel, it is said that there is vacuum in the vessel. The sound cannot travel through vacuum.