AP 9th Class Physics 11th Lesson Important Questions Sound

These AP 9th Class Physics Important Questions 11th Lesson Sound will help students prepare well for the exams.

AP 9th Class Physics 11th Lesson Sound Important Questions

Class 9 Physical Science Chapter 11 Important Questions – 2 Marks

Question 1.
What are transverse waves ?
Answer:
If the particles of a medium move perpendicular to the direction of the wave, the wave is called a transverse wave.
Ex : Light waves, sesmic waves.
Note : Transverse waves can’t be produced in a liquid or gas.

Question 2.
How does sound move through a medium ?
Answer:
When an object vibrates, it sets the particles of the medium around it vibrating and the disturbance created by the source of sound travels through the medium as a mechanical wave.

Question 3.
How are pressure and density related in sound propagation ?
Answer:
Pressure is related to the number of particles in a given volume of a medium, so more density of particles gives more pressure and vice versa and sound propagation can be visualized as the propagation of density or pressure variations in the medium.

Question 4.
How does the sound produced by a vibrating object in a medium reach your ear ?
Answer:
The sound wave created by the vibrating object travels through the medium as a series of compressions and rarefactions, ultimately reaching your ear and causing your eardrum to vibrate, which results in the perception of sound.

Question 5.
What are longitudinal waves ?
Answer:
Longitudinal waves are waves in which the particles of the medium oscillate back and forth in a direction parallel to the direction of propagation of the disturbance.

Question 6.
What is the difference between longitudinal and transverse waves ?
Answer:
In a longitudinal wave, particles of the medium oscillate back and forth along the direction of the wave’s propagation, whereas in a transverse wave, particles oscillate perpendicular to the direction of wave propagation.

Question 7.
How is the frequency of a sound wave defined ?
Answer:
The frequency of a sound wave is defined as the number of compressions or rarefactions that cross a point in the medium per unit time.

Question 8.
What is the relationship between wavelength and frequency of a sound wave ?
Answer:
The wavelength and frequency of a sound wave are inversely proportional to each other. This means that as the wavelength of a sound wave increases, its frequency decreases and vice-versa.

Question 9.
What is the difference between compression and rarefaction in a sound wave ?
Answer:
Compression is the region of a sound wave where the particles are crowded together and the pressure is high, whereas rarefaction is the region where particles are spread apart and the pressure is low.

Question 10.
What is the speed of sound and what factors affect it ?
Answer:
The speed of sound is the distance travelled by a sound wave per unit of time. The factors that affect the speed of sound are the temperature, humidity and density of the medium through which it is travelling.

Question 11.
How is the frequency of a sound wave related to its pitch?
Answer:
The frequency of a sound wave is directly proportional to its pitch. This means that as the frequency of a sound wave increases, its pitch also increases and as the frequency decreases, the pitch decreases.

Question 12.
How is the speed of sound affected by changes in temperature, humidity and medium density?
Answer:
The speed of sound is directly proportional to the temperature and humidity of the medium. As the temperature and humidity increase, the speed of sound also increases and vice-versa. The density of the medium also affects the speed of sound. As the density of the medium increases, the speed of sound decreases and vice-versa.

Question 13.
What is wavelength ? What are its units ?
Answer:

1. The distance between two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength.
2. The wavelength is usually represented by λ (Greek letter lambda).
3. Its S.I. unit is metre (m).

Question 14.
What is a frequency ? What are its units ?
Answer:

1. The number of such oscillations per unit of time is the frequency of the sound wave.
2. It is usually represented by v (Greek letter, nu). Its S.I. unit is hertz (symbol, Hz).

Question 15.
What is the time period of a sound wave ? What are its units ?
Answer:

1. The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave.
2. It is represented by the symbol T.
3. Its S.I. unit is second (s).

Question 16.
When does a high pitch of a sound wave produce ?
(OR)
What happens when more number of compressions and rarefactions passing a fixed point per unit time ?
Answer:

1. The faster the vibration of the source, the higher is the frequency and the higher is the pitch.
2. Thus, a high pitch sound corresponds to more number of compressions and rarefactions passing a fixed point per unit time.

Question 17.
When do sound of different pitch produce ?
Answer:
Objects of different sizes and conditions vibrate at different frequencies to produce sounds of different pitches.

Question 18.
What is amplitude ? What are its units ?
Answer:

1. The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave.
2. It is usually represented by the letter A
3. For sound its unit will be that of density or pressure.

Question 19.
What is the quality of sound ?
Answer:

1. The quality or timber of sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness.
2. The sound which is more pleasant is said to be of a rich quality.
3. A sound of single frequency is called a tone.

Question 20.
What is a note ? How is it different from a noise ?
Answer:
The sound which is produced due to a mixture of several frequencies is called a note and is pleasant to listen to music and noise is unpleasant to the ear.

Question 21.
Write the differences between loudness and intensity.
Answer:

1. Loudness is a measure of the response of the ear to the sound.
2. The amount of sound energy passing each second through unit area is called the intensity of sound.
3. Even, when two sounds are of equal intensity, we may hear one as louder than the other simply because our ear detects it better.

Question 22.
On which factors speed of sound depends ?
Answer:

1. The speed of sound in a medium depends on temperature of the medium.
2. In any medium as we increase the temperature, the speed of sound increases.
3. The speed of sound decreases when we go from solid to gaseous state.

Question 23.
What is the minimum distance required between the source of sound and the reflecting surface for hearing a distinct echo ?
Answer:
The minimum distance required between the source of sound and the reflecting surface for hearing a distinct echo is half the total distance covered by the sound from the point of generation to the reflecting surface and back, which is at least 17.2 m at a temperature of 22°C in air.

Question 24.
What is the minimum distance of the obstacle from the source of sound for hearing distinct echoes ?
Answer:
The minimum distance of the obstacle from the source of sound for hearing distinct echoes is 17.2 m, assuming a temperature of 22°C in air and a speed of sound of 344 m/s.

Question 25.
What is the time interval required between the original sound and the reflected one to hear a distinct echo ?
Answer:
The time interval required between the original sound and the reflected one to hear a distinct echo is at least 0.1 seconds.

Question 26.
How is excessive reverberation reduced in an auditorium or big hall ?
Answer:
Excessive reverberation is reduced in an auditorium or big hall by covering the roof and walls with sound-absorbent materials like, compressed fibreboard, rough plaster of draperies and selecting seat materials based on their sound absorbing properties.

Question 27.
Sometimes when cloudy we hear the rolling of thunder. How it happens ?
Answer:

1. Echoes may be heard more than once due to successive or multiple reflections.
2. The rolling of thunder is due to the successive reflections of the sound from a number of reflecting surfaces, such as the clouds and the land.

Question 28.
How do megaphones or loudhailers work ?
Answer:
Megaphones or loudhailers work by reflecting sound successively through a tube followed by a conical opening, which guides most of the sound waves from the source in the forward direction towards the audience.

Question 29.
Why are ceilings of concert halls, conference halls and cinema halls curved ?
Answer:
The ceilings of concert halls, conference halls and cinema halls are curved so that sound, after reflection, can reach all corners of the hall.

Question 30.
Describe the working of a stethoscope.
Answer:
In stethoscopes, the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflections of sound within the tube of the stethoscope. The sound is reflected back and forth within the tube, which amplifies the sound and directs it towards the doctor’s ears.

Question 31.
What is the purpose of using a curved soundboard in a hall ?
Answer:
The purpose of using a curved soundboard in a hall is to ensure that the sound, after reflecting from the soundboard, spreads evenly across the width of the hall. This helps in providing an optimal listening experience to all the audience members.

Question 32.
How do moths of certain families use their sensitive hearing equipment to escape capture ?
Answer:
Moths of certain families have very sensitive hearing equipment, which allows them to hear the high frequency squeaks of the bat and know when a bat is flying nearby and are able to escape capture.

Question 33.
How are ultrasonic waves used in industrial cleaning ?
Answer:
Ultrasonic waves, are used to clean objects in hard-to-reach places by sending waves through a cleaning solution. The high frequency of the waves causes particles of dust, grease and dirt to detach and drop out, leaving the object thoroughly cleaned.

Question 34.
How are ultrasonic waves used to detect flaws in metal blocks ?
Answer:
Ultrasonic waves are passed through a metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect. This technique is called ultrasonic testing or non-destructive testing.

Question 35.
How does echocardiography work ?
Answer:
Echocardiography is a medical imaging technique that uses ultrasonic waves to reflect from various parts of the heart and form art image. This technique helps in the diagnosis of various hear; conditions.

Question 36.
What are the applications of ultrasounds ?
Answer:
Ultrasound has various applications in industries and medical purposes. It can be used for cleaning hard-to-reach parts, detecting flaws in metal blocks, echocardiography, ultrasonography for imaging internal organs and breaking down kidney stones.

Question 37.
Write audible range of sounds of different animals.
Answer:
Dog – 50 kHz (ultrasound)
Bat – 100 kHz (ultrasound)
Dolphins – 150 kHz (ultrasound)
Rhinoceros – 5 Hz (Infrasound)
Note : We can communicate in space by using radio waves.

Question 38.
How do butterflies and insects like housefly, mosquito, bees, etc. produce a buzzing sound ?
Answer:
Butterflies and insects like housefly, mosquito, bees, etc. produce a buzzing sound by flapping their wings rapidly.

Question 39.
How can we describe a sound wave ?
Answer:
a) wavelength
b) amplitude
c) time period
d) frequency
e) speed.

Question 40.
Identify the following device. On which principle does it work ?

Answer:

1. This is a speaking tube.
2. It works on the principle of reflection of sound.

Question 41.
State the action and reaction in the following :
a) Moving rocket
b) Firing of a bullet from a gun
Answer:
a) Action – Force by burning fuel
Reaction – Rocket moving up

b) Action – Force on the bullet
Reaction – Force on the bullet pushes the gun backwards.

Question 42.
The below graph shows the displacement verses time relation for a disturbance travelling with a velocity of 1500 ms^-1.

Calculate the
a) Time period
b) Frequency
c) Wavelength of turbulence
Answer:
a) t = 2 seconds
b) v = \(\frac{1}{T}\) = \(\frac{1}{2}\) = 0.5 Hz ⇒ v = λv ⇒ 1500 = λ × 0.5 ⇒ λ = 1500 × \(\frac{1}{0.5}\)m
c) 3000 m.

Question 43.
Why is an echo weaker than the original sound ?
Answer:
This is because

1. sound spreads out in different directions and becomes weaker with distance. It loses some of its energy after colliding with other objects.
2. all of the sound waves don’t get reflected. Some of it gets absorbed.

Question 44.
Why do soldiery break step in marching over a bridge ?
Answer:
Soldiers break stbp in marching over a bridge in order to avoid resonance of the bridge. If the frequency of the soldier’s steps matches the natural frequency of the bridge, it will start shaking and might even collapse.

Sound Class 9 Important Questions – 3 Marks

Question 1.
Explain the concept of (i) wavelength and (if) amplitude and its significance in a sound wave.
Answer:
i) Wavelength is the distance between two consecutive compressions or rarefactions in a sound wave. It is significant because it determines the pitch of the sound. The longer the wavelength, the lower the pitch and the shorter the wavelength, the higher the pitch.

ii) Amplitude is the maximum displacement of the particles of a medium from their mean position when a sound wave passes through it. It determines the loudness of the. sound. The higher the amplitude, the louder the sound and the lower the amplitude, the quieter the sound.

Question 2.
What are the difference and similarities between the two waves given in the below diagrams ?

Answer:

1. Frequency and wavelengths are the same in both waves.
2. The amplitude of fig (a) is less than that of fig (b).
3. Fig (a) indicates a softer sound whereas fig (b) indicates a louder sound.
4. The pitch is the same in both waves.

Question 3.
What are the differehce and similarities between the two waves given In the below diagrams?

Answer:

1. Amplitude and loudness are same in the both waves.
2. The frequency of fig (c) is less than that of fig (d).
3. Fig (c) indicates a low-pitched sound whereas fig (d) indicates high pitched sound.
4. The pitch is different in both waves.

Question 4.
What is an echo ? Explain with an example. What is the condition to form an echo ?
Answer:

1. An echo is a sound that is heard again after it has been reflected off a suitable reflecting object, such as a tall building or a mountain.
2. If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound we hear is an echo.
3. The sensation of sound persists in our brain for about 0.1 s.
4. To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s or the minimum distance of the obstacle from the source of sound must be 17.2 m.

Question 5.
Observe the shapes of the instruments in the figure. Why is it made like that ?

Answer:

1. Megaphones or loudhailers, horns, musical instruments such as trumpets and shehnais, are all designed to send sound in a particular direction without spreading it in all directions.
2. In these instruments, a tube followed by a conical opening reflects sound successively to guide most of the sound waves from the source in the forward direction towards the audience.
3. They are working with multiple reflections.

Question 6.
What is the reason behind the delay between seeing a lightning flash and hearing the thunder ?
Answer:
1) The delay between seeing a lightning flash and hearing the thunder is due to the difference in speed between light and sound. Light travels at a much faster speed than sound, covering a distance of approximately 300,000 kilometres per second, while sound travels at a speed of approximately 340 metres per second.

2) This means that light from a lightning flash reaches our eyes almost instantly, while the sound of the thunder takes a few seconds to reach our ears, depending on the distance of the lightning.

Question 7.
Draw a sound wave and show the wavelength.
Answer:

Question 8.
Draw the wave diagrams of a low pitched sound and a high pitched sound.
Answer:

Question 9.
Draw the wave diagrams of a soft sound and a louder sound.
Answer:

Important Questions on Sound Class 9 – 5 Marks

Question 1.
What is a wave ? How can you say sound propagates in a medium in the form of waves ?
(OR)
How do particles behave in a medium while propagating sound ?
Answer:

1. A wave is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion.
2. They in turn produce similar motion in others.
3. The particles of the medium do not move forward themselves, but the disturbance is carried forward.
4. This is what happens during the propagation of sound in a medium, hence sound can be visualized as a wave.
5. Sound waves are characterized by the motion of particles in the medium and are called mechanical waves.

Question 2.
How does sound propagate in the air ?
(OR)
How are compressions and rarefactions formed in the air ?
Answer:

1. Air is the most common medium through which sound travels.
   When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called compression (C).
2. This compression starts to move away from the vibrating object.
3. When the vibrating object moves backward, it creates a region of low pressure called rarefa¬ction (R).
4. As the object moves back and forth rapidly, a series of compressions and rarefactions is created in the air.
5. These make the sound wave that propagates through the medium.

Question 3.
Write the differences between compressions and rarefactions.
Answer:

Compressions	Rarefactions
1) Regions of a longitudinal wave where the particles are com­pressed, or pushed closer together, than their equilibrium position.	1) Regions of a longitudinal wave where the particles are spread out, or pushed farther apart, than their equilibrium position.
2) In a sound wave, compressions cor­respond to areas of high pressure.	2) In a sound wave, rarefactions corres­pond to areas of low pressure.
3) The wavelength is measured from compression to compression.	3) The wavelength is measured from rarefaction to rarefaction.
4) In a transverse wave, there are no compressions or rarefactions; instead, there are crests and troughs.	4) In a transverse wave, there are no compressions or rarefactions ; instead, there are crests and troughs.

Question 4.
What is reverberation ? Explain with an example. How can it reduce ?
Answer:

1. The repeated reflection that results in this persistence of sound is called reverberation.
2. A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible.
3. In an auditorium or big hall excessive reverberation is highly undesirable.
4. To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fibreboard, rough plaster, or draperies.
5. The seat materials are also selected on the basis of their sound-absorbing properties.

Question 5.
How is ultrasonography used in medical imaging ?
Answer:

1. Ultrasonography is a medical imaging technique that uses ultrasonic waves to generate images of internal organs.
2. The ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density.
3. These waves are then converted into electrical signals that are used to generate images of the organ.
4. This technique helps in the detection of abnormalities, such as stones in the gall bladder and kidney or tumours in different organs.
5. It is also used for the examination of the foetus during pregnancy to detect.

Question 6.
Differentiate infrasound and ultrasound.
Answer:

	Infrasound	Ultrasound
Definition	Sound waves with frequencies below 20 Hz	Sound waves with frequencies above 20 kHz
Source	Natural sources (e.g., earthquakes, thunderstorms) and man-made sources (e.g., industrial machinery)	Medical and industrial devices (e.g., ultrasound machines)
Human Perception	Not heard by humans, but can be felt as vibrations in the body	Not heard by humans, but can be detected by some animals.
Applications	Used in seismology, weather moni­toring and studying animal commu­ication.	Used in medical imaging (e.g., sonograms) and industrial cleaning.

Question 7.
How does sound propagate in a medium ?
Answer:

1. Sound moves through a medium from the point of generation to the listener.
2. When an object vibrates, it sets the particles of the medium around it vibrating.
3. The particles do not travel all the way from the vibrating object to the ear.
4. A particle of the medium in contact with the vibrating object is first displaced from its equilibrium position.
5. It then exerts a force on the adjacent particle.
6. As a result of which the adjacent particle gets displaced from its position of rest.
7. After displacing the adjacent particle the first particle comes back to its original position.
8. This process continues in the medium till the sound reaches your ear.
9. The disturbance created by a source of sound in the medium travels through the medium and not the particles of the medium.

Question 8.
Write the differences between longitudinal waves and transversal waves.
Answer:

Longitudinal Waves	Transversal Waves
1) In longitudinal waves, particles of the medium oscillate parallel to the direction of wave propagation.	1) In transverse waves, particles of the medium Oscillate perpendicular to the direction of wave propagation.
2) Example : Sound waves	2) Example : Electromagnetic waves
3) Longitudinal waves can propagate through all types of media, includ­ing solids, liquids and gases.	3) Transverse waves can only propagate through solids and some liquids, but not through gases.
4) Waves propagate in the form of compression and rarefaction.	4) Waves propagate in the form of crests and troughs.
5) The wavelength is the distance between two consecutive compres­sions or rarefactions.	5) The wavelength is the distance between two consecutive crests or troughs.

Question 9.
Derive a formula for speed of a sound wave.
(OR)
Derive v = λυ
(OR)
Derive a relation among speed of wave, frequency and wavelength.
Answer:

1. The speed of sound is defined as the distance which a point on a wave, such as a compression or a rarefaction, travels per unit time.
2. We know, speed, v = distance / time.
3. v = λ/T
4. Here λ is the wavelength of the sound wave.
5. It is the distance travelled by the sound wave in one time period (T) of the wave.
6. We know that t> = 1/T (here υ = frequency)
7. Thus, υ = λ/T or v = λυ
8. That is, speed = wavelength × frequency

Question 10.
Draw the density and pressure variations of sound waves.
Answer:

Question 11.
Answer:

Echo	Reverberation
1) Produced by the reflection of sound from a suitable reflecting object.	1) Produced by the repeated reflection of sound from the walls, ceiling and other surfaces in a room.
2) Heard as a distinct sound that is delayed from the original sound.	2) Heard as a continuous sound that persists and overlaps with the original Sound.
3) Occurs when the time interval between the original sound and the reflected sound is at least 0.1 seconds.	3) Occurs due to the persistence of sound caused by repeated reflections.
4) Can be heard more than once due to successive or multiple reflections.	4) Can continue for several seconds after the source of sound has stopped.
5) Can be reduced by increasing the distance between the source of sound and the reflecting object.	5) Can be reduced by using sound- absorbent materials in the room.

Question 12.
Write some applications of multiple reflection of sound.
Answer:

1. Megaphones or loudhailers, horns, musical instruments such as trumpets and shehnais, are all designed to send sound in a particular direction without spreading it in all directions.
2. In stethoscopes the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflection of sound.
3. Generally, the ceilings of concert halls, conference halls and cinema halls are curved so that sound after reflection reaches all corners of the hall.
4. Sometimes a curved soundboard may be placed behind the stage so that the sound, after reflecting from the sound board, spreads evenly across the width of the hall:

Question 13.
What are the various applications of ultrasound technology and how do they work?
(OR)
Write some applications of ultrasounds.
Answer:
Ultrasound technology has a wide range of applications in different fields, such as industry and medicine. Some of the major applications of ultrasound are :

1) Cleaning : Ultrasound waves are used to clean parts that are difficult to reach, such as electronic components or odd-shaped parts. The high frequency of the waves causes the particles of dust, dirt and grease to detach and drop out, resulting in thoroughly cleaning.

2) Flaw detection : Ultrasound waves are used to detect cracks and flaws in metal blocks used for construction, bridges, machines and scientific equipment. The waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect.

3) Echocardiography : Ultrasound waves are made to reflect from various parts of the heart to form an image of the heart. This technique is called echocardiography and is used to diagnose heart abnormalities.

4) Ultrasonography : Ultrasound scanner is an instrument that uses ultrasonic waves to generate images of internal organs of the human body. The ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density. These waves are then converted into electrical signals that are used to generate images of the organ. This technique is called ultrasonography and is used to detect abnormalities, such as stones in the gall bladder and kidney or tumors in different organs.

5) Prenatal diagnosis : Ultrasonography is also used for examination of the fetus during pregnancy to detect congenital defects and growth abnormalities.

6) Lithotripsy : Ultrasound may be employed to break small “stones” formed in the kidneys into fine grains, which can then be flushed out with urine.

Question 14.
“A vibrating body produces the sound”. Prove it with an activity.
Answer:

• Take a tuning fork and set it vibrating by striking its prong on a rubber pad.
• Bring it near your ear.
• Hear the sound.
• Touch one of the prongs of the vibrating tuning fork with your finger and share your exper¬ience with your friends.
• Now, suspend a table tennis ball or a small plastic ball by a thread from support [Take a big needle and a thread, put a knot at one end of the thread and then with the help of the needle pass the thread through the ball].
• Touch the ball gently with the prong of a vibrating tuning fork.
• Observe what happens.
• The ball will move away every time on touching the tuning fork.

Question 15.
Can you produce sound without a vibrating object? Write an activity to explain how does sound produce.
Answer:

• Fill water in a beaker or a glass up to the brim.

• Gently touch the water surface with one of the prongs of the vibrating tuning fork, as shown in above figure.
• Next dip the prongs of the vibrating tuning fork in water, as shown in above figure.
• Observe what happens in both cases.
• When a vibrating tuning fork is touched to the water surface, the water starts vibrating, creating ripples on the surface.
• When the prongs of the vibrating tuning fork are dipped in water, the vibration of the fork is transferred to the water, creating larger ripples and waves.
• These vibrations produce sound.

Question 16.
Make a list of different types of musical instruments and discuss with your friends which part of the instrument vibrates to produce sound.
Answer:

ta

Question 17.
Write an activity to show the compressions and rarefaction.
Answer:

1. Take a slinky.
2. Ask your friend to hold one end.
3. You hold the other end.
4. Now, stretch the slinky as shown in Fig. (a).
5. Then give it a sharp push towards your friend.
6. Move your hand pushing and pulling the slinky alternatively and observe.
7. If you mark a dot on the slinky, you will observe that the dot on the slinky will move back and forth parallel to the direction of the propagation of the disturbance.
8. We can observe compressions and rarefactions in the slinky.
9. The regions where the coils become closer are called compressions (C) and the regions where the coils are further apart are called rarefactions (R).

Question 18.
How do you verify the laws of reflection of light in the case of sound instead of light?
Answer:

• Take two identical pipes, as shown in below figure.

• You can make the pipes using chart paper.
• The length of the pipes should be sufficiently long as shown.
• Arrange them on a table near a wall.
• Keep a clock near the open end of one of the pipes and try to hear the sound of the clock through the other pipe.
• Adjust the position of the pipes so that you can best hear the sound of the clock.
• Now, measure the angles of incidence and reflection and see the relationship between the angles.
• Lift the pipe on the right vertically to a small height and observe what happens. (In place of a clock, a mobile phone on vibrating mode may also be used.)
• Angle of incident of sound is equal to angle of reflected sound.
• We can here sound when two pipes and normal are in same plane.