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CHAPTER 13- SOUND, , Question 1. Choose the correct answer. Sound can travel through, , (a) gases only (b) solids only, , (c) liquids only (d) solids, liquids and gases (v7), , Question 2. Voice of which of the following is likely to have minimum frequency?, , (a) Baby girl (b) Baby boy (c) Aman (“%) (d) A woman, , 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), , (b) The number of oscillations per second of a vibrating object is called its time period. (F°), , (c) If the amplitude of vibration is large, sound is feeble. (F), , (d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T), , (e) The lower the frequency of vibration, the higher is the pitch, (F), , (f) Unwanted or unpleasant sound is termed as music. (F), , (g) Noise pollution may cause partial hearing impairment. (T), , Question 4. Fill in the blanks with suitable words., , (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., , (d) Unwanted sound is called Noise., , (ec) Shrillness of a sound is determined by the frequency of vibration, , Question 5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency., , Answer- Number of oscillations in 4 seconds = 40, 40, , Number of oscillations in 1 seconds = = = 10, , Therefore, frequency of pendulum = f= 10 Hz, , , , , , Now Time period =F = = = 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- Number of vibrations in 1 seconds = 500, , Therefore, frequency of vibration = f= 500 Hz, , Now Time period = ; += 0.002 sec., , , , 500, , Question 7. Identify the part which vibrates to produce sound in the following instruments., (a) Dholak, (b) Sitar, (c) Flute, Answer- (a) Dholak - Stretched membrane, , (b) Sitar - Stretched string., , (c) Flute - Air column., Question 8. What is the difference between noise and music? Can music become noise sometimes?

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Answer- The type of sound which is unpleasant to listen is known as noise whereas music is a pleasant sound,, which produces a sensation., , Yes, music can become noise when it’s too loud, , Question 9. List the sources of noise pollution in your surroundings., , Answer- Noise pollution sources are:, , (a) Bus and car horns., , (b) Firecrackers and loudspeakers., , (c) High volumes in televisions and DJ ete., , (d) Sound of kitchen appliances., , e) Sirens from factories, , Question 10. Explain in what way noise pollution is harmful to humans., , Answer- Noise pollution causes: (a) Lack of sleep, (b) Anxiety, — (c) Hypertension., , 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- | would suggest my parents to buy the house which is three lanes away from the roadside. This would, protect us from noise pollution which is maximum at roadside building., , Question 12. Sketch larynx and explain its function in your own words., , Answer- The other name of larynx is voice box. It is present at the upper end of the windpipe. The function of, , , , , , , , larynx is to produce sound with the help of two vocal cords on passing air., , Trachea, Vocal cord, , , , Larynx in human, , Question 13. 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- Speed of the light is much more than the speed of sound. Thus, lightning is seen earlier than thunder