Class 10 Physics Chapter 1 Notes Kerala Syllabus Sound Waves Questions and Answers

The comprehensive approach in SCERT Kerala Syllabus 10th Standard Physics Textbook Solutions and Class 10 Physics Chapter 1 Sound Waves Notes Questions and Answers English Medium ensure conceptual clarity.

SSLC Physics Chapter 1 Notes Questions and Answers Pdf Sound Waves

SCERT Class 10 Physics Chapter 1 Sound Waves Notes Pdf

SSLC Physics Chapter 1 Questions and Answers – Let’s Assess

Question 1.
Which of the following statements is correct?
a) Sound and light are transverse waves.
b) Sound and light are longitudinal waves.
c) Sound is a longitudinal wave and light is a transverse wave.
d) Sound is a transverse wave and light is a longitudinal wave.
Answer:
c) Sound is a longitudinal wave and light is a transverse wave.

Question 2.
The upper limit of frequency of sound that a bat can hear is 120 kHz. If so, what is the maximum wavelength of sound it can hear? Consider the speed of sound as 350 m/s.
Answer:
Frequency, f = 120 kHz = 120000 Hz
Speed of sound = 350 m / s
v = f λ
The maximum wavelength,
λ = v/f
= (350 m/s)/ 120000 Hz
= 0.0029 m
= 2.9 × 10^-3 m.

Question 3.
A graphic illustration of two waves travelling at a speed of 3.2 m/s is given.

Find out the frequency, period, and wavelength of each wave.
Answer:
(a) Figure 1.30 (a)
Speed of sound, v = 3.2 m / s
Frequency f = 1/8 Hz
period, T = 1 / f = 8 s
Wavelength, λ = v / f = (3.2 m / s) / (1/8 Hz)
= 3.2 × 8 = 25.6 m

(b) Figure 1.30 (b)
Speed of sound, v = 3.2 m / s
frequency, f = 1 Hz.
period, T = 1 / f = 1 s
Wavelength, λ = v / f = (3.2 m / s) / (1Hz) = 3.2 m.

Question 4.
Which of the following frequency can be heard by humans?
a) 5 Hz
b) 2000 Hz
c) 200 kHz
d) 50 kHz
Answer:
b) 2000 Hz

Question 5.
A wave has a frequency of 2 kHz and a wavelength of 35 cm. How far does this wave travel in 0.5 s?
Answer:
Frequency, f = 2 kHz = 2000 Hz
Wavelength, λ = 35 cm = 0.35 m
The wavelength, v = f λ = 2000 Hz × 0.35 m
= 700 m/s
Distance traveled per second = 700 m.
Distance traveled in 0.5 s = 700 / 2 = 350 m.

Question 6.
What is the frequency of a wave that produces 50 crests and 50 troughs in 0.5 s?
Answer:
Number of crests in 0.5 s = Number of troughs in 0.5 s = 50
Number of crests in 1 s = Number of troughs in 1 s = 100
Frequency of the wave = 100 Hz

Question 7.
Which of the following is different regarding the waves given in the figures 1.31 (a) and 1.31 (b)? (frequency, amplitude, wavelength)

Answer:
Amplitude

Question 8.
The distance between two adjacent troughs of a transverse wave is 2 m. Find the frequency if its speed is 20 m/s.
Answer:
Distance between two adjacent craters = 2 m.
The wavelength λ = 2 m
velocity v = 20 m / s
Frequency, f = v/λ = 20/2 m = 10 Hz.

Question 9.
When sound passes through a medium, ………………….. travels.
(the particles in the medium / the wave / the source of sound / the medium)
Answer:
The wave.

Question 10.
Two pith balls are suspended near the two prongs of a tuning fork fixed on a table so as to touch the prongs. A person plays a piano sitting near this system.
a) In this case the pith balls move slightly. What is the reason?
(forced vibration / echo)
b) While playing certain notes on the piano, the pith balls are thrown to a maximum distance. Which phenomenon is responsible for this? (reverberation / resonance)
Answer:
a) Forced vibration
b) Resonance

Physics Class 10 Chapter 1 Notes Kerala Syllabus Sound Waves

Question 1.
What type of motion does the swing have?
(circular/ oscillatory)
Answer:
Oscillatory
Observe the diagram showing the motion of the swing.

Question 2.
What is the initial position of the swing when it starts oscillating from its free state (equilibrium position)?
(A/O/B)
Oscillation is a periodic motion in which an object moves to and fro at regular intervals of time about its equilibrium position.
Answer:
O

Question 3.
In the figure, what is the maximum displacement to one side from the equilibrium position?
(2a, \(\frac{a}{2}[latex], a)
Answer:
a
The magnitude of maximum displacement to one side from its equilibrium position is amplitude. The symbol of amplitude is a. The SI unit of amplitude is metre (m).

Question 4.
When does the swing complete one oscillation?

(when the pendulum starts from O, reaches A and returns to O / when the pendulum starts from O, reaches A, then to B and back to O)
Answer:
When the pendulum starts from O, reaches A, then to B and back to O.

Question 5.
What if counting starts from A? When does the swing complete one oscillation?

Answer:
A swing completes one oscillation when it starts from A, reaches B and returns to A.
An oscillation is completed when the body returns to its initial position in the same direction from where it started.

Question 6.
Give more examples of oscillatory motion.
Answer:

• Motion of the pendulum of a clock.
• Movement of the cradle.
• Movement of the bob of the simple pendulum.
• The movement of the swing.

Question 7.
If a pendulum takes 1 minute to complete 30 oscillations, how long does it take to complete one oscillation?
Answer:
The time required for 30 oscillations = 1 minute = 60 s
Time required for 1 oscillation = [latex]\frac{60}{30}\) = 2 s
The time taken for one oscillation is called period. Its symbol is T.
SI unit of period is second (s).

Question 8.
Find the number of oscillations the same pendulum completes in one second.

Answer:
Number of oscillations in 1 minute (60 s) = 30
Number of oscillations in 1 second = \(\frac{60}{30}\) = \(\frac{1}{2}\) = 0.5
The number of oscillations in one second is called frequency.
The SI unit of frequency is hertz (Hz). Frequency is denoted by the letter f.

Simple Pendulum

Tie a bob to a string and hang it on a stand. This system is called a simple pendulum. Let’s find the period and frequency of a pendulum by swinging it at low amplitude.

Complete the table by doing an experiment using a simple pendulum, meter scale, and a stopwatch.

Question 9.
What is the change in frequency when the length 13. Excite tuning forks of different frequencies in a of the pendulum increases? similar manner and listen to the sound.
(increases / decreases) Do you feel any difference? What is the reason
Answer:
Decreases for the difference in sound here?
When the length of the pendulum increases, frequency decreases.

Question 10.
What is the relation between period and frequency?
Answer:
The time required for one oscillation = T
Number of oscillations per second = f
Frequency (f) = \(\frac{1}{\text { period }(T)}\)
As the period increases, frequency decreases.

Question 11.
Tuning forks are used for experiments connected with sound. Observe various tuning forks and note down the markings on each of them with their units .
Answer:
256 Hz, 288 Hz, 320 Hz, 341 Hz, 384 Hz, 480 Hz, 512 Hz

Question 12.
Is there any relation between the marking on the tuning fork and its number of vibrations?
Answer:
Yes. The marking on a tuning fork indicates the frequency of the tuning fork.

Question 13.
Excite tuning forks of different frequencies in a similar manner and listen to the sound.
Do you feel any difference? What is the reason for the difference in sound here?
Answer:
Difference in sound is felt. The difference in sound is due to the difference in frequency.
When an object vibrates freely, it vibrates in its innate frequency. This is the natural frequency of that object.

Factors that influence the natural frequency of an object:

• Length of the object
• Size of the object
• Elasticity
• Nature of the material etc
  Change in any one of these factors will affect the natural frequency of an object.

Question 14.
Do all objects vibrate only in their natural frequency?
Answer:
No, not all objects vibrate only at their natural frequency; they can also vibrate at forced frequencies.

Question 15.
Have you ever felt the vibration of the table when a mixie kept on the table works?
Answer:
The vibration of the table is also felt.

Question 16.
Excite a tuning fork and listen to it. What is the change in the sound heard when the stem of the excited tuning fork is pressed on the table?
Answer:
Sound becomes louder.

Question 17.
What could be the reason for the sound being louder?
Answer:
When the stem of the excited tuning fork is placed on the table, the table vibrates by the impulse of the tuning fork. The more the area of the table, the louder the sound.

In this case, the sound became louder because the table also vibrated along with the tuning fork.

Forced vibration is the vibration of an object induced by an external vibrating object.

Observe figure 1.5 (a).

Try the activities given below using the device in which two sets of three identical hacksaw blades each of length about 13 cm and 17 cm are fixed between two wooden blocks.

Question 18.
Excite the hacksaw blade A by tapping with your finger. What do you observe?
(all blades vibrate / only A vibrates)
Answer:
All blades vibrate.

Question 19.
Are all the blades vibrating with the same amplitude?
Answer:
No

Question 20.
Which of them vibrates with maximum amplitude?
Answer:
C, E

Question 21.
After all the blades have stopped vibrating, excite B and record the observation in the science diary.
Answer:
If B is vibrated after all the blades have stopped vibrating, then all the blades are vibrating and the blades D and F are vibrating at a higher frequency.

Question 22.
When blade A vibrates why would the hacksaw blades C and E vibrate with maximum amplitude?
Answer:
Since the natural frequency of C and E are equal to the natural frequency of A, they vibrate with maximum amplitude.

If the natural frequency of the forcing object and that of the forced object are equal, the objects are said to be in resonance. The objects undergoing resonance will vibrate with maximum amplitude.

Activity

Immerse in water a PVC pipe of about 50 cm length and 4 cm (11/2 inch) diameter. Excite a tuning fork of frequency 512 Hz and hold it close to the mouth of the pipe. Vary the length of the air column inside the pipe by gradually raising both the tuning fork and the pipe. We hear a louder sound at a particular stage. It is due to resonance.

Applications of forced vibration and resonance

• MRI scanning
• Radio tuning
• In musical instruments like guitar, violin, veena, harmonium, mridangam etc.
• We can hear even the faintest sound of the heartbeat when you listen to it using a stethoscope.
  A stethoscope used to listen to even a feeble sound in the body utilises forced vibration and resonance.
• In instruments like megaphones, horns and musical instruments such as trumpets and nagaswaram.

Question 23.
The frequency of a simple pendulum is 1 Hz. What is its period?
Answer:
Frequency = 1 Hz
Period (T) = \(\frac{1}{\text { frequency }}\) = \(\frac{1}{1}\) = 1 s

Question 24.
If apendulum takes 0.5 s to complete one oscillation, what is its frequency?
Answer:
The number of oscillations in 0.5 s = 1
Frequency = number of oscillations in 1 second = \(\frac{1}{0.5}\) = 2Hz

Question 25.
2 A tuning fork of frequency 512 Hz is excited and its stem is pressed on a table. Does the table vibrate in this situation? What is this phenomenon known as?
Answer:
The table vibrates, Forced vibration.
When a tuning fork of frequency 256 Hz vibrates, the air around it and the eardrum of the person hearing that sound vibrate 256 times per second.

Question 26.
How does the air near it vibrate when the tuning fork vibrates?
Answer:
When a tuning fork vibrates, it makes the air around it vibrates in the form of sound waves.

Question 27.
Do all these waves require a medium to travel?
Answer:
No
Complete table appropriately

Waves that require a medium for transmission	Waves that do not require a medium for transmission
Seismic waves	Radio waves
Sound waves	Light waves
Ripples off the surface of water

Electromagnetic waves
Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays are electromagnetic waves. They do not require a medium for transmission.

Mechanical Waves
Mechanical waves are those that require a medium for transmission. Mechanical waves are mainly of two types. They are longitudinal waves and transverse waves.

Longitudinal Waves
Question 28.
In figure 1.8 (b), did the coils in the slinky move parallel or perpendicular to the direction of propagation of the wave?
Answer:
In Figure 1.8 (b), the rings in the slinky move parallel to the direction in which the wave is moving.
Longitudinal waves are those in which the particles in the medium vibrate parallel to the direction of propagation of the wave.
Sound requires a medium for transmission. Let’s see how sound travels through air.

Observe the picture.

Question 29.
In figure 1.9, as the prong of the tuning fork moves from the equilibrium position to the side A, the air
pressure on that side ……………………..
(increases / decreases)
Answer:
Increases

Question 30.
What about the air pressure on side A when the same prong moves to side B?
Answer:
Decreases

Question 31.
When the prongs of the tuning fork vibrate continuously, aren’t regions of high and low pressure formed intermittently in the air?
Answer:
Yes, regions of high and low pressure formed intermittently in the air

Question 32.
Compare the wave produced in the slinky with the wave produced by the tuning fork in the air.
Answer:
Both are of the same type. In both, high-pressure and low-pressure areas are formed. In both of these the particles in the medium vibrate parallel to the direction of propagation of the wave.

Sound from a source creates continuous and regular pressure variations in the air. A region of high pressure is created where distance between the air molecules decreases. Such regions are called compressions (the region denoted by C in the figure 1.9) and a region of low pressure is called rarefactions (the region denoted by R in the figure 1.9). Sound travels through a medium forming alternating compressions and rarefactions.

Question 33.
What is the direction of motion of the particles in the string, with respect to the equilibrium position? (parallel / perpendicular)
Answer:
Perpendicular

Question 34.
Does each point on the string move parallel or perpendicular to the direction of propagation of the wave formed in the string?
Answer:
Perpendicular

Question 35.
Do the particles on the string undergo resultant translatory motion other than moving vertically up and down from their equilibrium position?
Answer:
No
When the particles of a medium vibrate perpendicular to the direction of propagation of the wave they are called transverse waves.

Question 36.
Are the coils moving parallel or perpendicular to the waveform created on the slinky?
Answer:
Perpendicular

Question 37.
What type of waveform is formed in the slinky?
Answer:

1. Transverse waves
2. Electromagnetic waves are transverse waves.

Question 38.
Some of the characteristics related to transverse waves and longitudinal waves are given below. Classify them and complete the table.
• Particles in the medium vibrate perpendicular to the direction of propagation of the wave.
• Compressions and rarefactions are formed.
• Pressure variations occur in the medium.
• Crests and troughs are formed.
• Particles in the medium vibrate parallel to the direction of propagation of the wave.
• No pressure variations occur in the medium.
Answer:

Longitudinal waves	Transverse waves
• Particles in the medium vibrate parallel to the direction of propagation of the wave.	• Particles in the medium vibrate perpendicular to the direction of propagation of the wave.
• Compressions and rarefactions are formed.	• Crests and troughs are formed.
• Pressure variations occur in the medium.	• No pressure variations occur in the medium.

Question 39.
In the figure, which are the points with maximum displacement from the equilibrium position of the wave?
(A, B, C, D, E)
Answer:
A, C, E

Question 40.
What is the amplitude of this wave?
Answer:
2 cm

Period
Question 41.
In figure 1.11, what is the time taken by the particle in the medium to complete one vibration?
Answer:
1 s

Question 42.
What is the period of the wave in the figure?
Answer:
1 s

Question 43.
If the wave shown in figure 1.11 takes 1 s to travel from O to D, find the frequency of the wave.
Answer:
1 Hz

Question 44.
In figure 1.13 (a), which particle is in the same phase of vibration as particle A?
(B, C, D, E)
Answer:
E

Question 45.
In the case of particle P?
Answer:
Q

Question 46.
In the case of particle B?
Answer:
F

Question 47.
In figure 1.13 (b), which represents the wavelength (2)?
(CR, RR)
Answer:
RR

Question 48.
Here CR represents (λ, \(\frac{\lambda}{2}\), \(\frac{\lambda}{4}\))
Answer:
\(\frac{\lambda}{2}\)

The distance between two consecutive compressions or two consecutive rarefactions is considered as the wavelength of a longitudinal wave.

Speed of wave
The speed of a wave is the distance travelled by the wave in one second.
The unit of speed of a wave is m/s.

Question 49.
If a wave travels 700 m in 2 s, what is the speed of the wave?
Answer:
The distance travelled by the wave in 2 s = 700 m
Wavelength = distance travelled per second
= \(\frac{700}{2}\) = 350 m

Is there a relation between frequency and wavelength?
Activity
Place a slinky on a table. Stretch both ends of it. Hold one end of the slinky and oscillate it to produce a transverse waveform. Then increase the frequency of oscillation. Observe the change in frequency and wavelength of the waveform generated in the slinky.

Observation
As the frequency increases, the wavelength decreases.
An illustration of two waves of the same amplitude passing through a medium at the same time interval is given.

Question 50.
In figure 1.14 (a), what is the wavelength of the wave?
Answer:
4 m

Question 51.
What is the wavelength of the wave in figure 1.14 (b)?
Answer:
2 m

Question 52.
In figure 1.14 (a), if both the waves take 1 s to travel a distance of 12 m, what is the frequency of the wave?
Answer:
3 Hz

Question 53.
In figure 1.14(b), What is the frequency of the wave?
Answer:
6 Hz

Question 54.
Which wave has a longer wavelength?
Answer:
Figure 1.14 (a)

Question 55.
Which wave has a higher frequency?
Answer:
Figure 1.14 (b)

Question 56.
What is the relation between wavelength and frequency?
Answer:
As the frequency increases, the wavelength decreases. Frequency decreases as the wavelength increases.

The time taken by both the waves to travel a distance of 12 m is equal. So the speed of the wave will be equal.

When the speed is constant, frequency of the wave is inversely proportional to the wavelength.
f = \(\frac{1}{\lambda}\)

The relation between the speed of wave, frequency and wavelength
Analyse figure 1.15 and answer the questions given below.

Question 57.
What is the wavelength (λ)?
Answer:
2 m

Question 58.
If the wave takes 1 s to reach A from O, what is the frequency (f)?
Answer:
f = 3 Hz

Question 59.
The speed of a wave the distance travelled by it in one second. What is the speed of the wave (v)?
It is found that the speed of a wave is the product of its wavelength and frequency.
Answer:
6 m/s
Speed of a wave = frequency × wavelength
ie, v = f λ

Question 60.
The state of the particles in a wave at a particular time is depicted in the figure.

a) How many crests are there in the figure?
b) How many troughs are there?
c) What is the wavelength?
Answer:
a) 3
b) 3
c) λ = 8 m

Question 61.
If the frequency of a longitudinal wave travelling at a speed of 350 m/s in the air is 35 Hz,
a) What is the distance between two consecutive compressions of this wave?
b) What about the distance between two consecutive rarefactions?
Answer:
a) Speed = 350 m/s
Frequency f = 35 Hz.
v = fλ
λ = \(\frac{v}{f}\) = 350/35 Hz = 10 m
Distance between two consecutive compressions = 10m

b) Distance between two consecutive rarefactions = 10m

Question 62.
A sound wave with a frequency of 175 Hz has a wavelength of 2 m. Calculate the speed of sound.
Answer:
Frequency = 175 Hz
Wavelength λ = 2 m
Speed of sound v = f λ = 175 Hz × 2 m = 350 m/s

Question 63.
Does sound from a source always travel directly to the listener?
Answer:
No
Reflected sound waves get reflected again.
This is multiple reflection of sound.

Echo
Question 64.
Have you ever had the experience of making a loud sound at the echo point and hearing the same sound again after a while?
Answer:
This is made possible by the phenomenon of echo.

While speaking loudly in a closed and empty large hall and calling or clapping loudly at a distance from a great mountain, isn’t it possible to hear the same sound again after a while? This is possible due to the phenomenon of echo.
Echo is the sound heard after a while due to the reflection of the initial sound.

Question 65.
What should be the minimum distance from the listener to the reflecting surface, if the first sound is to be heard distinctly after reflection?
Answer:
In order for the first sound to be heard clearly again after the echo, the echo should be at least half of 35 m (17.5 m) away from the listener. If the perimeter is more than 17.5 m, the same sound can be heard again separately.

The auditory experience produced by a sound persists for about \(\frac{1}{10}\) of a second. This characteristic is known as persistence of hearing. If another sound falls on the ear during this time, it is felt as if they are heard together.

Question 66.
How long will it take to hear the echo distinctly after hearing the first sound?
Answer:
\(\frac{1}{10}\)

Question 67.
How far does the sound travel during this time?
Answer:
(Consider the speed of sound in air as 350 m/s)
Distance = speed × time
= 350 m/s × (\(\frac{1}{10}\)) s = 35 m

For the echo to be heard, the reflecting surface must be at least 17.5m away, ie, half of 35 m. If the distance to the reflecting surface is more than 17.5 m, the same sound can be heard and distinguished again.

Question 68.
The echo of fire cracker (kathina) is heard after 1 s by the person who burst it. How far is the reflecting surface from the person hearing the echo? (speed of sound in air is 350 m/s).
Answer:
Let d be the distance to the reflecting surface. Then the total distance travelled by the sound to the reflecting surface and back will be 2d.
Speed of sound = \(\frac{\text { Total distance travelled }}{\text { Time }}\)
v = \(\frac{2 \mathrm{~d}}{t}\)
d = \(\frac{(\mathrm{v} \times \mathrm{t})}{2}\) = \(\frac{(350 \times 1) \mathrm{m}}{2}\) = 175 m
The reflecting surface will be 175 m away.

Question 69.
What should be the minimum distance between the source and the reflecting surface to hear the echo in water?
Answer:
(Consider the speed of sound in water as 1480 m/s)
v = 1480 m/s
v = \(\frac{2 \mathrm{~d}}{t}\)
2d = v × t = 1480 × \(\frac{1}{10}\) = 148 m
d = \(\frac{148}{2}\) = 74 m

Reverberation

Even if a small sound is produced inside the whispering gallery of Gol Gumbaz in Bijapur, Karnataka, it can be heard repeatedly throughout the gallery. This is due to the boom caused by the multiple reflections of sound waves on the spherical walls.

Reverberation is the lingering of sound, even after the original sound has ceased. It is due to the multiple reflection of sound and the boom fades away gradually.

Question 70.
WTiy are the walls of large halls like cinema theatres made rough?
Answer:
The walls of large halls, like cinema theaters, are often made rough or covered with sound-absorbing materials (like draperies or compressed fiberboard) to reduce reverberation and echoes, which can make sound unclear or unpleasant.

LIMITS OF AUDIBILITY
Note the limits of frequency of sound audible to humans in figure 1.22.

The frequency of sound produced in a galton whistle used for training dogs is about 30000 Hz.

Question 71.
Can humans hear the sound of a galton whistle?
Answer:
No
There are high and low-frequency sounds in nature. But humans cannot hear the sound of all frequencies. That is, there is a limit to the range of frequency of sounds that humans can hear. For a person with normal hearing, the lower limit of audible sound is about 20 Hz and the upper limit is about 20000 Hz (20 kHz). Sound with a frequency below 20 Hz is infrasonic. Sound with frequency more than 20000 Hz is ultrasonic.

Using ultrasonic sound, bats can travel smoothly and catch prey easily even in the dark. Ultrasonic waves are used in many situations.

Uses of Ultrasonic Waves
In the medical field, ultrasonic waves are used for diagnosis and treatment.

• To crush small stones in the kidneys.
• In physiotherapy.
• To take images of internal organs such as kidney, liver, gall bladder and uterus.

Ultrasonic waves that travel through body tissues strike and reflect at areas of varying density in the tissues. These waves are converted into electric signals to form an image of the organ. This technique is ultra sonography.

• For cleaning spiral tubes, irregular machine parts, electronic components etc.
• In the device called SONAR which is used to find the distance to the underwater objects.

Question 72.
If an ultrasonic wave emitted by a transmitter, installed on a ship on the surface of the water, strikes a rock at the bottom of the sea and returns after 0.2 s, what is the distance from the ship to the rock? Consider the speed of ultrasonic waves in seawater as 1522 m/s.
Answer:
v = 1522 m/s
t = 0.2 s
v = 2d/t
2d = v × t
d = (v × t)/2 = (1522 × 0.2)/2 = 152.2 m.

Question 73.
What measures can be taken to safeguard against tsunamis? Discuss.
Answer:

• When the tsunami warning is received from the official centers, it should be moved from the seashore to higher places.
• Wait for the official notification without deciding for yourself that the accident has been overcome.
• Try to protect yourself by not trying to pick up things in a rush to escape realize that life is important.
• In case of a tsunami, catch hold of any floating objects and escape.
• Follow the instructions given by the official tsunami warning centres.

Std 10 Physics Chapter 1 Notes – Extended Activities

Question 1.
Plan an activity that illustrates the resonance of sound.
Answer:
Materials

• A tuning fork (any pitch)
• A plastic or paper cup
• A rubber mallet or something to gently strike the tuning fork

Procedure

• Hit the Tuning Fork
  Gently strike the tuning fork with the mallet to make it vibrate.
• Bring It Close to the Cup
  Hold the vibrating tuning fork near the cup without touching it.
• Listen Closely
  You’ll hear the cup amplify the sound. Sometimes, the cup might even vibrate a little if it’s light enough.

Observation
The cup picks up the sound vibrations from the tuning fork. This is called resonance. The sound gets louder because the cup starts to vibrate at the same frequency.

Question 2.
Prepare and present a seminar paper on the topic: ‘Ultrasonic Waves and their Applications.’
Answer:
Brief Steps for Seminar Paper Presentation
1. Greeting & Introduction

• “Good morning, I’m [Your Name].”
• “My seminar topic is Ultrasonic Waves and Their Applications.”

2. Define the Topic

• Explain what ultrasonic waves are (sound waves > 20,000 Hz).
• Mention they are inaudible to humans.

3. Main Content (Key Points)

• Properties: High frequency, short wavelength, need a medium.
• Applications:
  Medical: Ultrasonography
  Industrial: Cleaning, testing
  Navigation: SONAR

4. Advantages & Limitations

• Advantages: Safe, accurate, non-invasive
• Limitations: Can’t travel in vacuum, needs coupling medium

5. Conclusion
• “Ultrasonic waves are useful in many fields and continue to grow in importance.”

6. Thank You
• “Thank you for listening. Any questions?”

Sound Waves Class 10 Notes

Sound Waves Notes Pdf

• Oscillation is a periodic motion in which an object moves to and fro at regular intervals of time about its equilibrium position.
• The magnitude of maximum displacement to one side from its equilibrium position is amplitude. The symbol of amplitude is a. The SI unit of amplitude is metre (m).
• The time taken for one oscillation is called period. Its symbol is T. The SI unit of period is second (s).
• The number of oscillations in one second is called frequency. The SI unit of frequency is hertz (Hz). Frequency is denoted by the letter f.
• When an object vibrates freely, it vibrates in its innate frequency. This is the natural frequency of that object.
• Factors that influence the natural frequency of an object are length of the object, size of the object, elasticity and nature of the material
• Forced vibration is the vibration of an object induced by an external vibrating object.
• If the natural frequency of the forcing object and that of the forced object are equal, the objects are said to be in resonance. The objects undergoing resonance will vibrate with maximum amplitude.
• When a tuning fork vibrates, it makes the air around it vibrates in the form of sound waves.
• The continuous propagation of energy from one part to the other parts through oscillations is called wave motion.
• Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays are electromagnetic waves. They do not require a medium for transmission.
• Mechanical waves are those that require a medium for transmission. Mechanical waves are mainly of two types. They are longitudinal waves and transverse waves.

INTRODUCTION

In this chapter, we will explore various concepts related to sound and waves. Sound is a form of energy that creates auditory perception. For sound to be audible, it requires a sound source, a medium, and a hearing organ. Topics such as oscillatory motion, frequency, period, natural frequency, forced vibration, resonance, wave motion, the characteristics of different types of waves, reflection of sound, reverberation, resonance, hearing range, and seismic waves were explained in this chapter in detail.

Oscillation

• Oscillation is a periodic motion in which an object moves to and fro at regular intervals of time about its equilibrium position.
• The magnitude of maximum displacement to one side from its equilibrium position is amplitude. The symbol of amplitude is a. The SI unit of amplitude is metre (m).
• The time taken for one oscillation is called period. Its symbol is T. The SI unit of period is second (s).
• The number of oscillations in one second is called frequency. The SI unit of frequency is hertz (Hz). Frequency is denoted by the letter f.
• When the length of the pendulum increases, frequency decreases. As the period increases, frequency decreases.
• When an object vibrates freely, it vibrates in its innate frequency. This is the natural frequency of that object.
• Factors that influence the natural frequency of an object are length of the object, size of the object, elasticity and nature of the material.
• Not all objects vibrate only at their natural frequency; they can also vibrate at forced frequencies.

Forced Vibration & Resonance

• Forced vibration is the vibration of an object induced by an external vibrating object.
• If the natural frequency of the forcing object and that of the forced object are equal, the objects are said to be in resonance. The objects undergoing resonance will vibrate with maximum amplitude.
• When a tuning fork vibrates, it makes the air around it vibrates in the form of sound waves.

Wave Motion

• The continuous propagation of energy from one part to the other parts through oscillations is called wave motion.
• Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays are electromagnetic waves. They do not require a medium for transmission.
• Mechanical waves are those that require a medium for transmission. Mechanical waves are mainly of two types. They are longitudinal waves and transverse waves.
• Longitudinal waves are those in which the particles in the medium vibrate parallel to the direction of propagation of the wave.
• Sound travels through a medium forming alternating compressions and rarefactions.
• When the particles of a medium vibrate perpendicular to the direction of propagation of the wave they are called transverse waves.
• In transverse waves, the elevated portions from the equilibrium position are called crests and the lowest portions from the equilibrium position are called troughs.

Characteristics of Waves

• The main characteristics of waves are amplitude, frequency, period, wavelength, speed of wave.
• The frequency of a wave is the number of cycles that pass through a point in one second.
• Amplitude is the maximum displacement from the equilibrium position of the wave.
• The distance between two consecutive compressions or two consecutive rarefactions is considered as the wavelength of a longitudinal wave. The Greek letter λ (lambda) is used to denote wavelength. The unit of wavelength is metre (m).
• The speed of a wave is the distance travelled by the wave in one second. The unit of speed of a wave is m/s. Speed of a wave = frequency × wavelength ie, v = fλ.

Reflection of Sound

• Smooth surfaces reflect sound more effectively than rough surfaces.
• Reflected sound waves get reflected again. This is multiple reflection of sound.
• Echo is the sound heard after a while due to the reflection of the initial sound.
• The auditory experience produced by a sound persists for about \(\frac{1}{2}\) of a second. This characteristic is known as persistence of hearing. If another sound falls on the ear during this time, it is felt as if they are heard together.
• For the echo to be heard, the reflecting surface must be at least 17.5 m away. If the distance to the reflecting surface is more than 17.5 m, the same sound can be heard and distinguished again.
• Reverberation is the lingering of sound, even after the original sound has ceased. It is due to the multiple reflection of sound and the boom fades away gradually.

Limits of audibility

• For a person with normal hearing, the lower limit of audible sound is about 20 Hz and the upper limit is about 20000 Hz (20 kHz). Sound with a frequency below 20 Hz is infrasonic. Sound with frequency more than 20000 Hz is ultrasonic.
• Ultrasonic waves are used to crush small stones in the kidneys, in physiotherapy, to take images of internal organs such as kidney, liver, gall bladder and uterus, for cleaning spiral tubes, irregular machine parts, electronic components etc.
• Ultrasonic waves that travel through body tissues strike and reflect at areas of varying density in the tissues. These waves are converted into electric signals to form an image of the organ. This technique is ultrasonography.
• Sonar is a device used to find the distance to the underwater objects.
• Seismic waves are those which travel through the Earth’s crust as a result of earthquakes, volcanic eruptions, and massive explosions. Seismology is the study of seismic waves. The intensity of earthquakes is determined by the Richter scale.
• Tsunami is a series of gigantic ocean waves caused by the displacement of large volumes of water in the sea.

WAVE MOTION
Experiment

Materials Required
1. A transparent tube about 75 cm long closed at one end
2. Light paper balls.
3. Unit of loudspeaker

Activity
Place light paper bas inside a long, transparent tube closed at one end. Pass a loud sound with uniform frequency through the free end of the tube.

Observation
The paper balls are seen vibrating back and forth from their equilibrium position. Without moving the paper balls to the other end, they are found to be close in some regions and apart in some other regions alternately. The approximate shape of the wave appears inside the tube.

Activity
Stretch both ends of a slinky placed on a table as shown in figure 1.8 (a).

Compress and release a few coils at one end of the slinky. Move one end of the slinky back and forth as shown in figure 1.8 (B).

Observation
Disturbances are formed in the slinky. The coils in the slinky do not move towards the other end with the disturbances occurring in slinky. It is seen that the disturbance formed in one part of the slinky spreads to the other parts without any displacement of the coil.

Here the energy received in one part of the medium spreads to the other parts by transferring it to the adjacent part and so on.

Wave motion is one of the modes of transfer of energy from one part of the medium to other parts.

The continuous propagation of energy from one part to the other parts through oscillations is called wave motion.

Some examples of waves are given below

• Radio waves
• Seismic waves
• Light waves
• Sound waves
• Ripples off the surface of water

Transverse Waves
Activity
Fix a spring vertically on a table using a nail. Tie one end of a string to the top of the spring and the other end to a 50 g slotted weight. Pass the string through the pulley fixed at the end of the table as shown in the figure.

Press and release the spring continuously.

Observation
As the spring is continuously compressed and released,
waves travel along the string to the pulley.

Observe the transverse waveform shown in figure 1.10 (b).

In transverse waves, the elevated portions from the equilibrium position are called crests and the lowest portions from the equilibrium position are called troughs. Place a slinky on a table. Stretch both ends of it. Hold one end of the slinky and oscillate it as shown in figure 1.10(c).

CHARACTERISTICS OF WAVES
The main characteristics of waves are :

• Amplitude
• Frequency
• Period
• Wavelength
• Speed of wave

Amplitude
The displacement-time graph of a particle in a wave is depicted.

Cycle
A cycle is one complete oscillation of a particle in wave motion.

Frequency
The frequency of a wave is the number of cycles that pass through a point in one second.

Wavelength
The state of the particles in a wave at a particular time is depicted in figure 1.13 (a).

Wavelength is the distance between two consecutive particles which are in the same phase of vibration. It is the distance travelled by the wave during the time taken by each particle in the medium to complete one vibration.

The distance between two consecutive crests or two consecutive troughs is also considered as the wavelength of a transverse wave.

The Greek letter λ (lambda) is used to denote wavelength. The unit of wavelength is metre (m).

REFLECTION OF SOUND
Do sound waves reflect when they hit objects? Let’s see.

Activity
Arrange two PVC pipes of 1 metre in length, a glass plate and an alarm clock as shown in the figure.

Adjust the pipe B at different angles and listen to the ticking sound from the clock. If the PVC pipes are arranged in such a way that the angle of fall and the angle of recoil are equal, the ticking sound from the alarm clock can be heard very clearly.

The sound is heard through the pipe B because sound waves reflect after striking the glass plate.

Repeat the experiment using rough surfaces instead of glass plate.

There is a decrease in the loudness of the reflecting sound. Smooth surfaces reflect sound more effectively than rough surfaces.

Smooth surfaces reflect sound more effectively than rough surfaces.

Reflection of sound is utilised in:

• Soundboards [Fig. 1.18 (a)]
• Curved ceilings in halls [Fig. 1.18 (b)]
  These help to reflect sound from a source and spread it to all parts of the hall.

Multiple Reflection of Sound
The figure shows how sound from a source reaches a listener in a closed hall.

Seismic Waves and Tsunami
Any type of wave above a certain intensity can cause harmful effects. There are also destructive waves.
A building that was destroyed by the earthquake is seen in figure 1.28.

Earthquakes often cause disaster.

Seismic waves are those which travel through the Earth’s crust as a result of earthquakes, volcanic eruptions, and massive explosions. Seismology is the study of seismic waves. The intensity of earthquakes is determined by the Richter scale.

Earthquakes that occur at the bottom of oceans or along coastal areas can sometimes trigger tsunami waves (Fig. 1.29). Tsunami is a series of gigantic ocean waves caused by the displacement of large volumes of water in the sea.