Chapter 11 : Sound

                    Chp11 :  Sound

                             Exercise Questions

Answer the following questions.

1. What is necessary condition for the production of sound?

Ans. Unlike light waves which are electromagnetic in nature and also can pass through vacuum,sound waves require some material medium for their propagation because it is mechanical wave.

2. What is the effect of the Medium on the Speed of Sound? In which medium sound travels faster: air, solid or liquid?

Ans. The nature of the medium will affect the speed of the sound waves. Sound will travel faster in solids as the particles of solid are tightly packed .Speed of sound in air is fifteen times greater than in gas while sound has five times greater speed in liquid than in gas. 

3. How can you prove the mechanical nature of sound by a simple experiment?

Ans.  Take an electric bell suspended in a bell jar with the help of two wires connected to power supply.By setting on power supply,electric bell will start ringing. Now start pumping the air out of the bell jar eventually the sound of electric bell will die out but if you pump back the air into the jar so again you will be able to hear the electric bell. This experiment of bell jar proves the mechanical nature of sound.

4.What do you understand by the longtudinal wave? Describe the longituinal nature of sound.

Ans. In longitudinal waves, the particles of medium move back and forth along the direction of the propagation of the waves

 Longitudinal Nature of Sound:

Direction of propagation of sound waves along oscillation or vibrating molecules.This shows the longitudinal nature of sound waves.

5. Sound is a form of wave.List some reasons to prove that sound is a wave.

Ans. Sound is form of wave, following are the reasons given below:

• It is produced by vibration of particles of medium
• Its is a carrier of energy
• Sound also manifest the phenomenon of diffraction, refraction and reflection.

6. We know that wave manifest the phenomenon of diffraction, relflection and refraction. Does sound also show these properties of waves?

Ans. Yes, like other waves sound also manifest the phenomenon of diffraction, relflection and refraction.

7. What is the difference between the intensity and loudness? Describe relation between the two terms.

Ans.  Intensity:

“Sound energy passing per second through a unit area held perpendicular to the direction of propagation of sound waves”. The basic units are (Wm-2).

        Loudness: 

“Loudness is the characteristic of sound by which loud and faint sounds can be distinguished”.

                           Relation between intensity and loudness

                   L - Lo = K (log I – log Io) = K log I /Io

8.  On what factors does the loudness of sound depend?

Ans. Loudness depends upon following factors:

• Area of vibrating body
• DIstsnce from vibrating body
• Amplitude of vibrating body

9. What do you mean by the term Intensity level of the sound? Name and define the unit of intensity level of sound.

Ans. As we know

                                L - Lo = K (log I – log Io) = K log I /Io

The difference (L - Lo) between the loudness (L) of an unknown sound and the

loudness Lo is called the intensity level of the unknown sound.

There are two unit of intensity level of sound: Bel and deciBel (dB)

10. What is difference between Frequency and Pitch?

Ans.  “Frequency is the number of occurrences of a repeating event per unit time” While

“Pitch of the sound is a characteristic of sound by which a shrill sound can be

distinguished from a grave one”.

11. Describe the effect of change in amplitude on loudness and the effect of change in frequency on pitch of sound.

Ans. The loudness of the sound varies directly with the amplitude of the vibrating

body. Higher amplitude has more loud sound.

Pitch of the sound varies directly with the frequency. A higher pitches means higher

frequency and vice versa.

12.Explain that Noise is a Nuisance?

Ans. “A noise nuisance is an annoyance or a noise that is audible”.

     Impacts of Noise:

The impact of noise on human health is a matter of great concern.

Noise pollution can affect us in several ways: Hearing problems, Poor cognitive function,

cardiovascular issues, Sleep disturbance, Trouble communication and Mental health

problem.

13. If the pitch of sound is increased, what are the changes in following:

Ans.    a) the frequency

As pitch is directly proportional to frequency hence the the increase in pitch will cause an increase in the frequency as well.

            b) the wavelength

With the increase in pitch there will be a decrease in wavelength.

            c) wave velocity

The  increase of pitch will cause an increase in wave velocity.

            d) amplitude of wave

The increase of pitch will have no effect on amplitude.

14. If we clap or speak in front of a building while standing at a particular distance, we rehear our sound after sometime. Can you explain how does this happen?

Ans. It is due to reflection of sound. When the sound is incident on the surface of the other medium it bounces back into its first medium which is known as relfection of light.

15. What is the Audible frequency range for Human Ear? Does this range vary with the age of people? Explain.

Ans. “The range of the frequencies which a human ear can hear is called the Audible

frequency range”.

A normal human ear can hear a sound only if its frequency lies between

20Hz and 20,000Hz.Different people have different range of audibility. It also decreases

with age. Young children can hear sounds of 20,000 Hz but old people cannot hear

sounds even above 15,000 Hz.

16.  Describe the importance of Acoustic Protection?

Ans.  Acoustic has a great importance in our daily life.

• Office equipment’s has increased significantly, the noise level remained almost the same.
• Productivity increases when the noise level decreases at the work place.
• Indoor environment of all places of work must ensure that people feel healthy both in mentally and physically terms. 

17. What are the uses of ultrasound in medicines ?

Ans. Some few uses of Ultrasound in Medicine are:

• Ultrasound is used to diagnose and treat different ailment.
• Ultrasounds are used to help a doctor to evaluate the flow of blood in the vessels.
• The heart can also be studied by using an ultrasound.
• Ultrasound is a helpful way to observe many of body’s internal organs.