WBBSE Solutions For Class 9 Physical Science Chapter 7 Human Ear And Sound Pollution

Chapter 7 Human Ear And Sound Pollution Synopsis

There are two major functions of the human ear:

1. Hearing and
2. Maintaining balance of the body.

Human ear can be divided into three parts:

1. Outer ear,
2. Middle ear and
3. Inner ear.

The middle ear consists of three bones:

1. Malleus,
2. Incus and
3. Stapes

1. The narrow passage from the pharynx to the cavity of the middle ear is known as the eustachian tube. It is a canal that connects the middle ear to the pharynx. Its main function is to maintain the equilibrium of the air pressure between the inside and outside of the middle ear.
2. The inner ear mainly consists of the vestibular apparatus and cochlea.
3. The last part of the inner ear that looks like a coiled tube similar to a snail is known as the cochlea. The organ which acts as the receptor of sound in the cochlea is called the organ of Corti.
4. The minimum intensity of, sound that produces a sensation of sound in the human ear is known as the threshold of hearing.
5. The threshold of hearing for a sound wave frequency 1000 Hz is I₀ = 10^-12 W/m².
6. This is known as zero-level intensity.
7. The maximum intensity for a sound of frequency 1000 Hz is 1 W/m², which a person can tolerate safely.
8. The relationship between the loudness L and intensity I is L = k • log I, k is a constant of proportionality.

If at a given frequency, l₁, l₀ be the intensities and L₁, L₀ be the loudness of two sound waves respectively, then,

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⇒ \(L_1=k \log _{10} l_1 \text { and } L_0=k \log _{10} l_0\)

Hence the difference in the loudness of the two sounds is \(L=L_1-L_0=k \log _{10}\left(\frac{I_1}{I_0}\right)\)

If I₀ is taken as the reference intensities (10^-12  W • m^-2)

i.e., the minimum intensity of audible sound at frequency 1 kHz, then L is called the sound level,

Taking k = 1, the sound level is

L = \(1 \cdot \log _{10}\left(\frac{I_1}{I_0}\right)\)

= \(10 \cdot \log _{10}\left(\frac{l_1}{l_0}\right) \cdot \frac{1}{10}\) bel

L = \(10^{\circ} \cdot \log _{10}\left(\frac{I}{I_0}\right)\) decibel

For \(I=I_0 \quad L=10(1) \log _{10}=0 \mathrm{~dB} .\)

i.e., the sound of intensity 10^-12 W/m² at 1 kHz frequency has zero loudness. For increase in intensity at a point by 10 times the initial value, the increase in sound level will be 10log₁₀10 = 10 dB

The unit of loudness level is decibel. 1dB = 1/10 B

The harmful effect of undesirable sound on the environment is known as sound pollution. Undesirable sound refers to sound with high loudness and pitch and beyond the tolerance level of the ear.

World Health Organisation (WHO) has prescribed a safe intensity level of 45 dB and if the intensity of sound exceeds a level of 65 dB, it is detrimental to the health of human beings. Our hearing capacity may be permanently damaged if the intensity level rises to 150 dB-160 dB.

Chapter 7 Human Ear And Sound Pollution Short And Long Answer Type Questions

Question 1. What are the functions of a human ear?

Answer:

Functions Of A Human Ear:-

There are two major functions of a human ear:

1. Hearing and
2. Maintaining balance of the body.

Question 2. Draw a simple figure depicting different parts of a human ear.

Answer:

Different Parts Of A Human Ear Are Shown In Below:- 

The figure depicting different parts of a human ear is shown below:

Question 3. Describe the structure and function of the outer ear of a human being.

Answer:

Structure And Function Of The Outer Ear Of A Human Being:-

The outer portion of the ear is called outer ear. It consists of three parts

1. Pinna
2. Auditory canal and
3. Tympanic membrane or eardrum.

Pinna is made up of a thin plate of yellow elastic cartilage and soft tissue and is situated on two sides of the head. At the centre of the pinna, there is a hole which is connected with a 3 cm long zigzag canal named auditory canal which extends up to the eardrum (tympanic membrane).

The tympanic membrane is situated at the end of the auditory canal and is an elastic membrane mainly made up of muscles.

The pinna of ear collects external sound waves and reflects it to auditory canal. Sound waves, after passing through the auditory canal, create vibration on the tympanic membrane.

Question 4. What is pinna or auricle?

Answer:

Pinna:-

This is a portion of the outer ear protruding outwardly on two sides of the head. It is made up of a thin plate of yellow elastic cartilage, covered with an integument, and connected to the surrounding parts by ligaments and muscles.

Question 5. Describe the structure and function of the middle ear of a human being.

Answer:

Structure And Function Of The Middle Ear Of A Human Being:-

In between the outer ear and the inner ear, there lies the middle ear which consists of a small air-filled cavity and is made up of three adjacent bones — malleus, incus and stapes.

As the middle ear is connected with the pharynx through the eustachian tube, air pressure remains the same inside and outside the middle ear.

The vibrations that are created by an external sound wave in the eardrum enters the inner ear through the bones of the middle ear.

Question 6. Describe the structure and function of the inner ear of a human being.

Answer:

Structure And Function Of The Inner Ear Of A Human Being:-

The inner ear consists mainly of the vestibular apparatus and cochlea. There are three semicircular canals in the vestibular apparatus. These semi-circular canals are filled up with a liquid named endolymph.

The cochlea is the last part of the inner ear and looks like a coiled tube similar to a snail. The organ which acts as the receptor of sound in the cochlea is called the organ of Corti. It is a hairy instrument with three compartments filled with endolymph.

When a sound wave reaches the cochlea, the organ of the Corti is stimulated and this stimulation reaches the hearing centre of the brain through auditory nerves and creates the sensation of hearing.

Question 7. What is the role of the ear in sending sound waves?

Answer:

Role Of Ear In Sending Sound Waves:-

The pinna of the ear collects external sound waves and reflects it to the external auditory canal. It gathers sound energy and focuses it on the eardrum to vibrate it.

This vibration on the eardrum created by the external sound waves enters the inner ear through three tiny bones – malleus, incus and stapes of the middle ear.

When sound reaches the cochlea of the inner ear, the organ of Corti is stimulated and this stimulation reaches the hearing centre of the brain through auditory nerves and creates the sensation of hearing.

Question 8. What is the eustachian tube? What is its function?

Answer:

Eustachian Tube:-

It is a narrow passage from the pharynx to the cavity of the middle ear. It is a canal that connects the middle ear to the pharynx.

Its main function is to maintain the equilibrium of the air pressure between the inside and outside of the ear. Its secondary function is to clear any accumulated secretion, infection or debris from the space of the middle ear.

Question 9. What do you mean by sound pollution?

Answer:

Sound Pollution:-

The harmful effect of undesirable sound on the environment is known as sound pollution. Undesirable sound refers to sound with high loudness and pitch and beyond the tolerance level of the ear.

The sound produced by different factories, horns of traffic, loudspeakers used in various functions, fire-crackers, take-off and landing of aircraft, loud sounds from radio, television, sirens etc. create sound pollution in the environment.

Further, natural sources like the sound of lightning, and the rumbling of clouds also add to sound pollution.

Question 10. How does sound pollution happen in our daily lives?

Answer:

Sound Pollution Happen In Our Daily Lives As Follows:-

In daily life, our hearing gets so used to different high-pitched sounds that we get tremendous relief when these sounds stop.

Different aspects of our environment are responsible for the mental and physical health of every animal on the planet. Sound is one of the key features among them.

Different types of undesirable high-pitched sounds like noise, shouting, the sound of microphones, the sound of cars, the sound of air-horns, the sound of generators, and metallic and mechanical sounds from different factories and from different other sources get mixed together to disturb our normal life.

If the same type of disturbance continues in the same area regularly, it creates sound pollution. Mental and physical health is affected due to this sound pollution.

Question 11. Discuss in brief, the harmful effects of sound pollution on the animal world of the earth.

Answer:

Harmful Effects Of Sound Pollution On The Animal World Of The Earth:-

It has been observed in very recent research works that not only human beings but also other animals are badly harmed due to sound pollution created by humans.

Research has proved that a particular species of frog is used to hear calls of a specific low frequency from their friends.

However, due to sound pollution, the frogs are forced to communicate with other frogs in high-frequency sound which disrupts their normal livelihood. Birds also suffer due to the same reason.

The harmful effects of sound pollution extend to the deep sea also. Normal lives of whales, dolphins, fish etc. suffer enormously due to ultrasonic sounds from SONAR emitted on account of scientific research in deep seas Discuss the harmful effects of sound pollution in daily life.

Question 12. Discuss the harmful effects of sound pollution in daily life.

Answer:

Harmful Effects Of Sound Pollution On Daily Life:-

Sound pollution is harmful to human beings, both physically and mentally. It has been observed that the hearing power of a man is damaged if a high-pitched sound is heard continuously for a long time. In extreme cases, it may also lead to deafness.

The high-pitched sound may increase blood pressure, create heart problems, and affect the concentration of the mind and also memory. Work efficiency gradually decreases if a person is a victim of sound pollution due to professional reasons. Sound pollution is an important cause of insomnia.

Question 13. Discuss some ways to control sound pollution in our daily lives.

Answer:

Ways To Control The Sound Pollution In Our Daily Lives Are:

1. By increasing awareness among the citizens regarding sound pollution and its bad effects.
2. By taking preventive measures in factories regarding sound pollution.
3. By making laws regarding sound pollution and implementing those rigorously.
4. By prohibiting the use of loudspeakers and horns of car near schools, colleges, hospitals etc,
5. By constructing factories and airports away from the residential areas.

Question 14. What do you mean by the threshold of hearing? What is the maximum intensity of sound that a person can tolerate safely?

Answer:

Threshold Of Hearing And The Maximum Intensity Of Sound That A Person Can Tolerate Safely:-

The threshold of hearing is the minimum intensity of sound that produces a sensation of sound in the human ear. For a sound wave of frequency 1000 Hz, the threshold of hearing is given by, I₀ = 10^-12 W/m²

This is also known as zero-level intensity.

The maximum intensity for a sound of frequency 1000 Hz is 1 W/m², which a person can tolerate safely.

Chapter 7 Human Ear And Sound Pollution Very Short Answer Type Questions Choose The Correct Answer

Question 1. The ‘Decibel’ unit is used to measure

1. Loudness
2. Frequency
3. Wavelength
4. Time period

Answer: 1. Loudness

Question 2. What is the safe intensity level of sound indicated by the World Health Organisation (WHO)?

1. 45 dB
2. 65 dB
3. 80 dB
4. 90 dB

Answer: 1. 45 dB

Question 3. What is the sound intensity level of perception?

1. 100 dB
2. 110 dB
3. 120 dB
4. 140 dB

Answer: 3. 120 dB

Question 4. What is the threshold of hearing for sound with a frequency of 1000 Hz?

1. 10^-9 W/m²
2. 10^-10 W/m²
3. 10^-11 W/m²
4. 10^-12 w/m²

Answer: 4. 10^-12 w/m²

Question 5. What is the limit of perception for sound of frequency 1000 Hz?

1. 1 W/m²
2. 1.5 W/m²
3. 2W/m²
4. 10 W/m²

Answer: 1. 1 W/m²

Question 6. What is the unit of intensity of sound in SI?

1. W • m^-2 • K^-1
2. W • m^-2
3. W • m^-1
4. W • m^-1 • K^-1

Answer: 2. W • m^-2

Question 7. What is the dimensional expression of the intensity of sound?

1. MT^-3
2. MT^-2
3. MLT^-3
4. ML^-1T^-3

Answer: 1. MT^-3

Question 8. What is the persistence time of hearing?

1. 0.05 s
2. 0.1 s
3. 0.2 s
4. 1s

Answer: 2. 0.1 s

Question 9. It is the function of _____ to collect and centralise sound waves.

1. Pinna
2. Auditory canal
3. Tympanic membrane or eardrum
4. Tympanic cavity

Answer: 2. Auditory canal

Chapter 7 Human Ear And Sound Pollution Answer In Brief

Question 1. Which quantity has its unit as decibel?

Answer: Decibel (dB) is the unit of difference of intensity level of sound.

Question 2. Between loudness and intensity of sound, which one is a measurable quantity?

Answer: The intensity of sound is a measurable quantity.

Question 3. Where is the organ of Corti located?

Answer: The organ of Corti is located in the cochlea of the inner ear.

Question 4. What is endolymph?

Answer:

Endolymph

Endolymph is a liquid which is present in the scala media cavity of the cochlea in the inner ear in which the organ of Corti remains immersed.

Question 5. Where is the semicircular canal located in the ear?

Answer: The semicircular canal is located in the inner ear.

Question 6. What is a basilar membrane?

Answer:

Basilar membrane

The basilar membrane is a membrane in the cochlea on which the organ of Corti is located.

Question 7. What is the function of the auditory canal of the ear of a human being?

Answer: The auditory canal of the ear collects and focuses sound waves.

Question 8. What is the function of the tympanic cavity of the ear of a human being?

Answer: Waves created on the tympanic membrane vibrate the air of the tympanic cavity and sound waves move forward towards the next portion of the ear.

Question 9. What is the function of a eustachian tube of the ear of a human being?

Answer: The eustachian tube maintains the equilibrium of air pressure between the inside and the outside of the middle air.

Question 10. What are the different parts of the human ear?

Answer:

There are three main parts of the human ear, which are:

1. The outer ear
2. The middle ear
3. The inner ear.

Question 11. What are the three bones of the middle ear?

Answer: The three bones of the middle ear are malleus, incus and stapes.

Question 12. What is the function of the ear other than hearing?

Answer: In addition to hearing, the ear maintains the balance of the body.

Chapter 7 Human Ear And Sound Pollution Fill In The Blanks

Question 1. _______ maintain air pressure in the middle ear.

Answer: Eustachian tubes

Question 2. The unit of the difference of intensity levels of sound is ______

Answer: Bel

Question 3. The ear can mainly be divided into _______ parts.

Answer: Three

Question 4. Sound waves reach the auditory centre of the brain through ______ nerves.

Answer: Auditory

Question 5. The unit of intensity of sound is _______

Answer: W/m²

Question 6. The safe level of noise is ________ dB.

Answer: 65 db

Question 7. The part of the human ear that collects the sound and sends it to the auditory canal is _______

Answer: Pinna

Question 8. The vibrations produced by the eardrum are amplified by the _______, _________ and _______

Answer: Hammer, Anvil, The stirrup

Question 9. The _______ is a coiled and fluid-filled tube having the sense organ of hearing.

Answer: Cochlea

Chapter 7 Human Ear And Sound Pollution State Whether True Or False

Sound Exercise

Question 1. The ear only helps us to hear.

Answer: False

Question 2. The eustachian tube maintains pressure balance on the two sides of the eardrum.

Answer: True

Question 3. The three ossicles the hammer, anvil and the stirrup are located at the inner ear.

Answer: False

Question 4. The cochlea is a coiled and fluid-filled tube.

Answer: True

Question 5. The organ of Corti is located in the mammalian cochlea.

Answer: True

Question 6. The incus receives vibrations from sound pressure on the ear drum.

Answer: False

Question 7. Zero-level sound intensity is 10^-12W • m^-2.

Answer: True

Question 8. The safe level of noise as specified by the central pollution control board is 120 dB.

Answer: False

Chapter 7 Human Ear And Sound Pollution Miscellaneous Type Questions

Match the Columns

1.

Answer: 1. A, 2. C, 3. B, 4. D

2.

Answer: 1. B, 2. C, 3. D, 4. A