Sound

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In-Text Questions and Answers

  1. Question: How do you come to know that a ‘period’ is over in your school?
    Answer: We know that a period is over when we hear the school bell ring.
  1. Question: How is sound produced? How does it travel from one place to another? How do we hear sound? Why are some sounds louder than others?
    Answer: Sound is produced when objects vibrate. It travels from one place to another through a medium like air, water, or solids. We hear sound when these vibrations reach our ears and make our eardrums vibrate. Some sounds are louder than others because they have larger vibrations (amplitude).
  1. Question: Touch the school bell when not in use. What do you feel? Again touch it when producing sound. Can you feel it vibrating?
    Answer: When the school bell is not in use, it feels still and does not vibrate. When it is ringing and producing sound, we can feel it vibrating.
  1. Question: Do you hear a sound? Touch the plate or pan gently with your finger. Do you feel the vibrations? Again strike the plate with the stick and hold it tightly with your hands immediately after striking. Do you still hear the sound? Touch the plate after it stops producing sound. Can you feel the vibrations now?
    Answer: Yes, when we strike the plate, we hear a sound. When we touch it gently, we can feel the vibrations. If we hold the plate tightly after striking, the sound stops, and we cannot feel the vibrations anymore.
  1. Question: Do you hear any sound? Does the band vibrate?
    Answer: Yes, when we pluck the rubber band, we hear a sound. The rubber band vibrates when it is plucked.
  1. Question: Do you hear a sound? Again strike the dish and then touch it. Can you feel the dish vibrating? Strike the dish again. Look at the surface of water. Do you see any waves there? Now hold the dish. What change do you observe on the surface of water? Can you explain the change? Is there a hint to connect sound with the vibrations of a body?
    Answer: Yes, when we strike the dish, we hear a sound. When we touch it, we can feel it vibrating. We also see waves on the surface of the water when we strike the dish. If we hold the dish, the vibrations stop, and the waves on the water disappear. This shows that sound is produced by vibrations.
  1. Question: When we speak, does any part of our body vibrate?
    Answer: Yes, when we speak, our vocal cords in the throat vibrate to produce sound.
  1. Question: Do you feel any vibrations?
    Answer: Yes, if we place our fingers on our throat while speaking or singing, we can feel vibrations.
  1. Question: Do you hear any sound? Our vocal cords produce sound in a similar manner.
    Answer: Yes, when we blow air through stretched rubber bands or a slit in paper, we hear a sound. This is similar to how our vocal cords vibrate when air passes through them to produce sound.
  1. Question: How does the sound propagate or travel to her?
    Answer: Sound travels through the air from our mouth to our friend’s ears as vibrations.
  1. Question: Does the sound become fainter as you suck air? Remove the tumbler from your mouth. Does the sound become loud again? Can you think of an explanation? Is it possible that the decreasing amount of air in the tumbler had something to do with decreasing loudness of the ring?
    Answer: Yes, the sound becomes fainter as we suck air from the tumbler. When we remove the tumbler, the sound becomes loud again. This happens because sound needs air (a medium) to travel. When there is less air, the sound becomes fainter.
  1. Question: Can you hear the sound of the bell? Does it indicate that sound can travel through liquids?
    Answer: Yes, we can hear the sound of the bell inside the water. This shows that sound can travel through liquids.
  1. Question: Can you hear the sound of the scratching? Ask your friends around you if they were able to hear the same sound?
    Answer: Yes, we can hear the sound when we place our ear on the scale or table. Our friends who are not touching the scale may not hear it. This shows that sound can travel through solids.
  1. Question: Can you say that sound can travel through strings?
    Answer: Yes, in a toy telephone made with strings and cups, sound travels through the string when we speak, showing that sound can travel through strings (solids).
  1. Question: How do we hear it?
    Answer: We hear sound when vibrations in the air reach our ears and make our eardrums vibrate. These vibrations are sent to the brain, and we hear the sound.
  1. Question: Observe what happens to the grain. Why do the grains jump up and down?
    Answer: When someone speaks into the can covered with a rubber sheet and grains on top, the grains jump up and down. This happens because the sound vibrations make the rubber sheet vibrate, causing the grains to move.
  1. Question: Every day you hear the voices of children and adults. Do you find any difference in their voices? Can you say that the frequency of the voice of a child is higher than that of an adult?
    Answer: Yes, children’s voices are usually higher-pitched than adults’. This means that the frequency of a child’s voice is higher than that of an adult.
  1. Question: Can we hear the sound of all vibrating bodies?
    Answer: No, we cannot hear all sounds. Humans can hear sounds with frequencies between 20 Hz and 20,000 Hz. Sounds outside this range are inaudible to us.
  1. Question: Is the sound always pleasing? Does a sound sometimes cause discomfort to you?
    Answer: No, not all sounds are pleasing. Some sounds can be unpleasant or cause discomfort, like loud horns or construction noise.
  1. Question: Are the sounds coming from the construction site pleasing? Do you enjoy the sounds produced by horns of buses and trucks? In a classroom, if all the students speak together, what would the sound produced be called?
    Answer: No, the sounds from a construction site or loud horns are not pleasing. If all students speak together in a classroom, the sound would be called noise.
  1. Question: What sources in the home may lead to noise?
    Answer: In homes, loud televisions, music systems, kitchen appliances like mixers, and air conditioners can produce noise.
  1. Question: What are the Harms of Noise Pollution? Do you know that presence of excessive noise in the surroundings may cause many health-related problems?
    Answer: Yes, excessive noise can cause health problems like lack of sleep, stress, high blood pressure, and hearing loss.
  1. Question: How can the noise pollution be controlled in a residential area?
    Answer: Noise pollution can be controlled by reducing loud sounds, using silencers in machines, planting trees, and keeping noisy activities away from residential areas.

Exercise Questions and Answers

  1. Question: Sound can travel through(a) gases only(b) solids only(c) liquids only(d) solids, liquids, and gases
    Answer: (d) solids, liquids, and gases
  1. Question: Voice of which of the following is likely to have minimum frequency?(a) Baby girl(b) Baby boy(c) A man(d) A woman
    Answer: (c) A man
  1. Question: 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)
    Answer: True (T)(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
    Answer: False (F)

    (c) If the amplitude of vibration is large, sound is feeble. (T/F)
    Answer: False (F)

    (d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
    Answer: True (T)

    (e) The lower the frequency of vibration, the higher is the pitch. (T/F)
    Answer: False (F)

    (f) Unwanted or unpleasant sound is termed as music. (T/F)
    Answer: False (F)

    (g) Noise pollution may cause partial hearing impairment. (T/F)
    Answer: True (T)

  1. Question: Fill in the blanks with suitable words.
    (a) Time taken by an object to complete one oscillation is called __________.
    Answer: Time period(b) Loudness is determined by the __________ of vibration.
    Answer: Amplitude

    (c) The unit of frequency is __________.
    Answer: Hertz (Hz)

    (d) Unwanted sound is called __________.
    Answer: Noise

    (e) Shrillness of a sound is determined by the __________ of vibration.
    Answer: Frequency

  1. Question: A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
    Answer:

    • Frequency = Number of oscillations / Time takenFrequency = 40 oscillations / 4 seconds = 10 Hz
    • Time period = 1 / FrequencyTime period = 1 / 10 Hz = 0.1 seconds
  1. Question: 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:

    • Frequency = 500 Hz
    • Time period = 1 / FrequencyTime period = 1 / 500 Hz = 0.002 seconds
  1. Question: Identify the part which vibrates to produce sound in the following instruments.
    (a) Dholak
    Answer:     Stretched membrane (skin) on both sides.
    (b) Sitar
    Answer: Stretched strings.
    (c) Flute
    Answer: Air column inside the flute vibrates.
  1. Question: What is the difference between noise and music? Can music become noise sometimes?
    Answer:

    • Difference: Noise is an unpleasant and unwanted sound, while music is a pleasant and soothing sound that is organized and has rhythm.
    • Can music become noise? Yes, if music is played too loudly or inappropriately, it can become unpleasant and be considered noise.
  1. Question: List sources of noise pollution in your surroundings.
    Answer:

    • Loudspeakers at high volume
    • Heavy traffic with honking vehicles
    • Construction activities
    • Loud music from radios or TVs
    • Industrial machinery
  1. Question: Explain in what way noise pollution is harmful to humans.
    Answer:Noise pollution can cause:

    • Stress and irritation
    • Lack of sleep
    • Headaches
    • High blood pressure
    • Hearing loss or impairment
  1. Question: 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:I would suggest buying the house three lanes away from the roadside because it will be quieter. Living away from the main road reduces noise pollution from traffic, making it a more peaceful and healthier place to live.
  1. Question: Sketch larynx and explain its function in your own words.
    Answer:(Draw yourself.)The larynx, or voice box, is located in our throat. It contains two vocal cords that vibrate when air passes through them, producing sound. The muscles can tighten or loosen the cords to change the pitch of the sound we make when we speak or sing.
  1. Question: Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
    Answer:Light travels much faster than sound. So, when lightning strikes, the light reaches us almost instantly. Sound travels slower, so we hear the thunder after a short delay. That’s why we see lightning before we hear the thunder.

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