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Q1. What are audible vibrations?

Solution

The vibrations whose frequencies are from 20 Hz to 20,000 Hz constitute the audible vibrations. Human ear can can only recognise these vibrations.

Q2. Can sound travel in vacuum? Explain

Solution

Sound cannot travel in vacuum because sound travels by producing a vibration in the molecules of the medium surrounding it and there are no molecules in vacuum.

Q3. How does the pitch of the sound depend on its frequency?

Solution

The pitch of sound depends on the frequency of vibration. The higher the frequency the more shrill is the sound and vice versa.

Q4. Name the unit for the measurement of loudness of sound.

Solution

Loudness of sound is measured in decibels (dB). A sound of about 50 to 80 decibels is considered as audible sound.

Q5. We cannot talk to one another on the surface of moon. Give reasons.

Solution

Sound requires a medium to propagate. It cannot travel in vacuum. Since there is vacuum on the moon therefore, the sound of other person does not reach to our ear, so we cannot talk to one another on the surface of moon.

Q6. What determines the shrillness of the sound produced by a body?

Solution

Shrillness of the sound produced by a body is determined by the frequency of the vibrating body.

Q7. What are the three main causes of oceanic sound pollution?

Solution

Oceanic sound pollution is caused by (i) under water blasting, (ii) dredging and (iii) under water earthquakes.

Q8. Give reasons for the following. A fighter aeroplane is seen before hearing its sound.

Solution

1. A fighter aeroplane is seen before hearing its sound because light travels at a very high speed of 3x10⁸ m/s whereas the sound travels in air at 330m/s. Thus as soon as a fighter plane appears it is seen at once whereas its sound takes some time to reach us.

Q9. How are the sound waves propagated by a telephone speaker?  

Solution

A speaker speaks out his words and those words are converted into electrical signals which are then carried great distances and then received by the listener. The signals are then converted back to sound and that sound is heard to the listener.

Q10. Name one material that do not conduct sound and act as sound insulator?

Solution

Cork does not conduct sound and acts as sound insulator.

Q11. What are the effects of noise on the animals?

Solution

Noise can have a detrimental effect on animals (i) by causing stress, (ii) increasing risk of death by changing the delicate balance in predator/prey detection and avoidance, and by interfering with their use of sounds in communication especially in relation to reproduction and in navigation. (iii) acoustic overexposure can lead to temporary or permanent loss of hearing.

Q12. (i) What determines the shrillness of the sound produced by a body?(ii) What are the three main causes of oceanic sound pollution?

Solution

(i) Shrillness of the sound produced by a body is determined by the frequency of the vibrating body.(ii) Oceanic sound pollution is caused by (a) under water blasting, (b) dredging and (c) under water earthquakes.

Q13. How do wind instruments make sound?

Solution

Wind instruments, like the flute and trumpet, vibrating air makes the sound. The air particles move back and forth creating sound waves. Blowing across a flute's hole sets up slinky-like waves in the tube. In the clarinet, a vibrating reed (a thin piece of wood set in the mouthpiece) gets the waves started. Different pitches are played by pressing keys that open or close holes in the tube making the air column inside the tube longer or shorter.

Q14. A large drum can produce a larger sound than a small drum, give reason..

Solution

 Loudness depends on the area of the vibrating body. Thus, loudness increases with an increase in the area of vibrating body. A large drum occupies more area than a small drum therefore, a large drum can produce a larger sound than a small drum.

Q15. Pick the odd one out and state the reason for your choice: Time period, Pitch, Shrill, Loudness.

Solution

Loudness. Loudness is a phenomenon pertaining to amplitude of the sound while the rest are related to its frequency.

Q16. Your parents are going to buy a house. They have been offered one house on the roadside and another house three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.

Solution

I would suggest my parents to buy the house which is three lanes away from the roadside. This is because being away from the busy road will reduce noise pollution caused by heavy traffic on the road.

Q17. What is a vibration?

Solution

A vibration is defined as a rapid back and forth movement of a body about a central position.

Q18. what will happen if we would be able to hear infrasonic and ultrasonic sound ?

Solution

Infrasonic sound waves have smaller frequency so if they were heard by humans , human beings would find minute disturbance which is not loud. Ultrasonic sound waves, being a high frequency wave would cause a loud disturbance if humans were to hear them. However on hearing these sound waves humans would find it very difficult to communicate as they would be burdened with additional sound which will create a huge disturbance in sensing sound waves from audible range

Q19. Name the steps taken by city administration to control noise pollution.

Solution

Most city ordinances prohibit sound above threshold intensity from trespassing over property line at night, typically between 10 p.m. and 6 a.m., and during the day restrict it to a higher sound level. They also put restriction on types of horns used and kinds of vehicles allowed.

Q20.  Define:(a) Amplitude(b) Time period(c) Frequency

Solution

(a) Amplitude: The maximum displacement from the mean position during an oscillation is called the amplitude of the oscillation. (b) Time period: The time taken to complete one oscillation is called the time period of the oscillation. (c) Frequency: The number of oscillations per second is called the frequency of oscillation.

Q21. How does a sound wave travel through the air?

Solution

Sound waves travel through the air by vibrating or moving the particles of matter in the air.

Q22. How is sound produced in humans?

Solution

Larynx is the organ that is involved in the production of sound in humans. It is also called as voice box. The voice box is situated in the neck at the upper end of the wind pipe. The sound produced is controlled by vocal cords which are thin membranes stretched across the voice box. There are muscles that are attached to the vocal cords. These muscles can vary the tension in the vocal cords. With the help of these muscles we can make different sounds.

Q23. What do u understand by sources of sound? Give any two examples.

Solution

Objects that produce sound are called sources of sound. For example: musical instruments, audio players etc.

Q24. Differentiate between wind instrument and percussion instrument.

Solution

Wind instrument These musical instruments are generally made in the form of pipes. When we blow air into them, column inside vibrates producing note. Whistle, flute and shehnai are some common wind instruments.   Percussion instrument In these instruments, we make a leather membrane vibrate by striking it with a hammer or with our hands. Drum, tabla and dholak are commonly used percussion musical instruments.

Q25. What is noise pollution?

Solution

 Noise pollution: Sustained presence of harmful, unwanted or annoying noise in the environment is called noise pollution.

Q26. Name the key sources of urban noise pollution.

Solution

The source of most noise pollution worldwide is (i) Transportation systems, including motor vehicle noise, aircraft noise and rail noise. (ii) Factory noise, (iii) Loudspeaker usage and (iv) Festive cracker bursting are some other causes.

Q27. Differentiate between Intensity and Loudness.

Solution

Intensity of sound at a point is defined as the amount of sound energy flowing per second normally through unit area around that point. Loudness is a measure of amount of sensation produced in the ears of the listener. Intensity does not depend on the listener whereas the loudness depends on the listener.

Q28. The time period of a vibrating body is 0.0002 sec. Calculate its frequency.

Solution

5000 Hz. Frequency is inverse of time period or the number of vibrations per second. Hence Frequency = 1/T = 1/0.0002 = 5000/sec or Hz

Q29. Do you know why bees buzz? Is it the way they communicate?

Solution

No, bees do not communicate by buzzing. Buzzing sound of bees is produced by their mouths. The buzzing comes from the wings of the bee, which it flaps even while feeding on the nectar of a flower.

Q30. State whether the following statement is true or false:Sound can travel through liquids and gases but not through solids.

Solution

  FalseSound can travel through solids, liquids and gases.

Q31. How does percussion instrument produce sound? Give 2 examples also.

Solution

Percussion instruments produce sound by being struck, shaken, scraped or clashed together. Examples: Xylophone, gong, table, conga, drums

Q32. Name few common NO HORN zones in a city.

Solution

NO HORN zones in a city are (i) Schools, (ii) Hospitals, (iii) Aged Homes, (iv) Places of worship,

Q33. Sound cannot reach us from space. Give reasons.

Solution

Sound requires a medium to propagate. It cannot travel in vacuum. Since there is a vacuum in space, therefore, sound cannot reach us from space.

Q34. Define:Noise

Solution

 Noise: Unwanted, discomfort causing sound from any source is called noise.

Q35. Name some common ailments suffered by people living in a residential area close to the airport.

Solution

Common ailments suffered by people living in a residential area close to the airport are (i) Irritability, (ii) Cardio vascular disease, (iii) Hypertension, (iv) Lack of sleep (v) Hearing impairment.

Q36. List the factors on which the speed of propagation of sound depends on?

Solution

Speed of propagation of sound depends on(i) Temperature(ii) Nature of the media(iii) Humidity

Q37. Define shrill and sound quality.

Solution

Shrill: The sound produced by a vibrating object with a high frequency is called shrill. Sound quality: The quality of a musical sound is that characteristics by virtue of which we can distinguish between two sounds of the same pitch and loudness produced by two different musical instruments or by different voices.

Q38. Does sound travel faster than the speed of light?

Solution

No. Sound travels about 750 miles/hour, while light travels about 770 million miles/hour. That's about a million times faster.

Q39. Define pitch and timbre.

Solution

1. Pitch is the effect or sensation produced in the brain due to the sound of some particular frequency. Pitch depends upon the frequency of a vibrating body. It means that higher the pitch more is the frequency and lower the pitch less is the frequency. 2. Timbre or sound quality is that characteristics by virtue of which we can distinguish between two sounds of the same pitch and loudness produced by two different musical instruments or two different voices.

Q40. What is the speed of sound in air?

Solution

Speed of sound in air is 340 m/s.