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Class 9 Sound Waves Characteristics and Applications Worksheet
Worksheet On Sound Waves Characteristics and Applications Class 9
Sound Waves Characteristics and Applications Worksheet Class 9
→ Sound: A form of energy produced by vibrations capable of being heard by the human ear.
→ Vibration: The periodic to-and-fro motion of an object about its mean position.
→ Energy: The ability to do work or bring about change.
→ Production of Sound: The generation of sound through vibrating objects.
→ Tuning Fork: A U-shaped metallic instrument that produces sound when set into vibration. Propagation of Sound: The movement of sound waves through a medium.
→ Medium: The material (air, water, or solid) through which sound travels.
→ Average Density: The normal density of a medium without any disturbance.
→ Compression: A region where particles are closely packed in a sound wave.
→ Rarefaction: A region where particles are spread apart in a sound wave.
→ Sound Wave: A disturbance that travels through a medium due to vibrations of particles.
→ Longitudinal Waves: Waves in which particles vibrate parallel to the direction of wave propagation. Mechanical Waves: Waves that require a medium to travel.
→ Transverse Waves: Waves in which particles vibrate perpendicular to the direction of wave propagation.
→ Crest: The point of maximum density or pressure in a sound wave graph.
→ Trough: The point of minimum density or pressure in a sound wave graph.
→ Wavelength (A): The distance between two consecutive compressions or consecutive rarefactions in a sound wave.
→ Frequency (f or U): The number of oscillations or vibrations produced per second, measured in hertz (Hz).
→ Time Period (T): The time taken for one complete oscillation of the wave.
→ Amplitude (A): The maximum variation in density or pressure of the medium from its average value during the propagation of a sound wave.
→ Intensity: The amount of sound energy passing through a unit area per unit time.
→ Speed of Sound: The distance travelled by sound per unit time.
→ Relation between Speed, Wavelength and Frequency: Speed (v) = wavelength (λ) × frequency (f).
→ Pitch: The sensation that allows us to judge a sound as high or low, determined by its frequency.
→ Infrasonic Wave: Sound waves with a frequency below 20 Hz, inaudible to humans.
→ Ultrasonic Wave: Sound waves with a frequency above 20 kHz, also inaudible to humans.
→ Loudness: The perception of the strength or intensity of sound dependent on amplitude.
→ Reflection of Sound: The bouncing back of sound from a surface, obeying the laws of reflection.
→ Echo: The repetition of sound due to reflection from a distant surface.
→ Reverberation: The persistence of sound due to multiple reflections in a large hall or an auditorium.
→ Echolocation: The method used by certain animals (e.g. bats, dolphins) to locate objects by emitting sound waves and detecting their reflections.
→ Sonar (Sound Navigation and Ranging): A technique that uses sound waves to detect underwater objects.
Class 9 Science Exploration Chapter 10 Worksheet
Class 9 Science Sound Waves Characteristics and Applications Worksheet
A. Multiple-Choice Questions
Question 1.
The speed of sound depends upon the
(a) temperature of the medium
(b) pressure of the medium
(c) temperature of the source producing sound
(d) temperature and pressure of the medium.
Question 2.
Loud sound can travel a large distance because of its
(a) low amplitude
(b) high frequency
(c) high energy
(d) highspeed.
Question 3.
To hear a distant echo, the minimum time interval between the original sound and its reflected sound must be
(a) 0.2 s
(b) 1 s
(c) 2 s
(d) 0.1 s
Question 4.
Multiple reflection of sound is not used in
(a) stethoscope
(b) trumpet
(c) megaphone
(d) telescope.
Question 5.
The unit of frequency is
(a) Hertz (Hz)
(b) Joule (J)
(c) Decibel (dB)
(d) Meter (m).
Question 6.
Humans adapted the principle of sound reflection in underwater exploration through
(a) radar
(b) sonar
(c) periscope
(d) telescope.
Question 7.
Astronauts cannot hear each other directly in outer space because of
(a) no gravity
(b) no air medium
(c) low temperature!
(d) no energy.
Question 8.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose
the appropriate answer.
Assertion (A): Compressions are regions of low pressure in a sound wave.
Reason (R): In compressions, particles of the medium are closer together.
(a) Both A and R are true and R is the correct explanation of A. E
(b) Both A and R are true but R is not the correct explanation of A. E
(c) A is true but R is false. E
(d) A is false but R is true. E
Question 9.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose
the appropriate answer.
Assertion (A): Ultrasonic waves cannot be heard by humans.
Reason (R): Their frequency is higher than 20,000 Hz.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A. E
(c) A is true but R is false. E
(d) A is false but R is true. fl
Question 10.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose
the appropriate answer.
Assertion (A): Echolocation can determine the position of an object.
Reason (R): Reflected sound waves carry information about distance and direction.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A. E
(c) A is true but R is false.
(d) A is false but R is true. E
B. State True (T) or False (F).
Question 1.
Bats use visible light to locate prey at night.
Question 2.
Echolocation is not useful in underwater detection.
Question 3.
The crest represents the region of maximum density in a sound wave graph.
Question 4.
Sound travels in vacuum with maximum speed.
Question 5.
The number of density oscillations at a fixed point per unit time is the frequency of the sound wave.
C. Fill in the blanks.
Complete the following with a suitable word/words:
Question 1.
If 40 compressions pass a point in 4 seconds, the frequency is ________ Hz.
Question 2.
Breaking kidney stones using sound is done with _______ waves.
Question 3.
Sound waves are ______ waves, meaning particles vibrate parallel to the direction of wave travels.
Question 4.
Speed of sound is fastest in ________ medium.
Question 5.
An ________ is the repetition of a sound due to the reflection of sound waves off a hard, distant surface.
D. Assign one word to the following.
Question 1.
The lowest point on a sound wave graph, representing minimum density.
Question 2.
Maximum displacement of particles from their mean position during vibration.
Question 3.
Distance between two consecutive compressions in a sound wave.
Question 4.
Inverse of frequency representing the time taken for one complete oscillation.
Question 5.
Waves used for detecting earthquakes.
E. Match the Column I with Column II.
Question 1.
| Column I | Column II |
| (i) Echo | (a) Persistence of sound in large halls |
| (ii) Reverberation | (b) Reflection of sound |
| (iii) Sonar | (c) Frequency greater than 20 kHz |
| (iv) Ultrasonic waves | (d) Underwater navigation using sound |
F. Very Short Answer Type Questions
Question 1.
Define vibration, amplitude and time period.
Question 2.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Question 3.
State the relation between wavelength, frequency and speed of sound in a given medium.
G. Short Answer Type Questions
Question 1.
From the diagrams shown below, identify which waves represent high-pitched sounds and which represent low-pitched sounds. For each case, give the reason.
Question 2.
The variation of density of medium for a sound wave propagating with a speed of 340 m s-1 is shown in figure. Calculate the wavelength and frequency of the sound wave.
Question 3.
An echo returns in 3 seconds. What is the distance of the reflecting surface from the source given that the speed of sound is 342 m/s?
H. Long Answer Type Questions
Question 1.
(a) Explain the working of a SONAR with the help of a well-labelled diagram.
(b) A sonar device on a submarine sends out a signal and receives an echo 5 seconds later. Calculate the speed of sound in water, if the distance of the object from the submarine is 3,625 m.
Question 2.
The sound of an explosion on the surface of a lake is heard by a boatman 100 m away and a diver 100 m below the point of explosion.
(a) Who will hear the sound of the explosion first?
(b) If sound takes t seconds to reach the boatman, how much time (approximately) will it take to reach the diver?
Question 3.
A vehicle is fitted with an ultrasonic distance sensor as part of parking assistance system which provides echolocation, while the driver is reversing the vehicle. It emits ultrasonic wave (about 40 kHz) which is reflected by the obstacle. When the warning beep starts sounding at a distance of 1.2 m from the obstacle, how much time is taken by ultrasonic wave to travel to the obstacle and come back? Assume the speed of ultrasonic wave in air to be 345 m s-1.
Wonder Why
A. Give reasons for the following.
Question 1.
Astronauts doing a spacewalk outside the International Space Station cannot directly hear each other speak, even though they are just a few metres apart.
Question 2.
Sound is heard more clearly at night than during the day, even when the source is at the same distance.
Question 3.
An empty vessel makes a louder sound than a filled one when struck.
Question 4.
Walls, floors, and ceilings of concert halls and auditoriums are lined with soft, porous materials such as foam panels, curtains, and upholstered seats.
Question 5.
A bat can navigate and hunt in complete darkness without colliding with any object, even though its eyes are very small.
Learn By Doing
A. Label the following diagrams.
Question 1.
The diagram shows a longitudinal sound wave. Label the compressions (C), rarefactions (R), one complete wavelength (λ), and the direction of wave propagation.
Question 2.
The diagram below illustrates the structure of the human ear. Label part A Briefly describe the role of each part in the process of hearing sound.
B. The table below presents data on sound frequencies emitted by different sources, as recorded during an experiment. The speed of sound in air is 344 ms-1.
Study the data and answer the following questions:
| Sound source | Frequency (Hz) |
| Tuning Fork A | 256 |
| Tuning Fork B | 512 |
| Bat ultrasound | 50000 |
| Elephant call | 14 |
Question 1.
Calculate the wavelength for each sound source using v = λν.
Question 2.
Calculate the time period of each sound wave. Which sound wave has the longest time period?
Question 3.
Which of the four sounds can the human ear detect? Justify your answer using the audible frequency range.
Explore with Curiosity
A. Study the density-distance graph of a sound wave and answer the questions.
Question 1.
The sound waves emitted by three sources A, B and C are represented in Fig. If the frequency of A is maximum and C is minimum, identify the corresponding curves, and mark A, B and C on them.
Question 2.
How would the above density-distance graph differ for the sound waves having larger amplitude? Sketch or describe it.
B. Analyse and answer.
Question 1.
The speed of sound in steel is 5000 m s-1 and in air is 340 m s-1. Two friends stand 340 m apart along a steel railing. One taps the steel railing with a hammer. Calculate the time taken for sound to reach the other friend through the railing.
Question 2.
A school bell rings in the corridor. Richa, standing inside the corridor, hears it clearly. Samir, sitting on the sports ground outside, also hears it. Explain how the sound reaches each listener. Which listener is likely to hear the bell more loudly, and why?
Question 3.
A ship’s SONAR detects a submarine. The ultrasonic pulse returns after 1.2 seconds. Speed of sound in seawater is 1530 m s. Find the distance of the submarine from the ship.
C. Read the paragraph and answer the following questions.
The Gol Gumbaz in Bijapur, Karnataka, is renowned for its extraordinary acoustics. The dome, one of the largest in the world, creates a uWhispering Gallery” inside the mausoleum. A whisper spoken near the wall on one side can be heard clearly on the opposite side, about 37 metres away, even without any amplification. This happens because the curved dome reflects sound waves along its inner surface, concentrating them back towards the listener.
Multiple reflections cause the sound to be heard as many as seven times. The same principle, though undesirable in large halls, leads to reverberation, when reflected sounds overlap so closely that speech becomes unclear. Modern architects control this using sound-absorbing panels, curtains, and carpeted floors to achieve a balance of clarity and richness of sound.
Question 1.
Using the concept of reflection of sound, explain how the ‘Whispering Gallery’ in Gol Gumbaz works.
Question 2.
Why is the same phenomenon that creates the ‘Whispering Gallery’ considered undesirable in a lecture hall or cinema?
Question 3.
What materials are used in modern auditoriums to reduce unwanted reverberation? Explain why these materials are effective.
Suggested Activities
A. Take two paper cups and make a small hole in the base of each. Thread a long piece of string (about 5-10 m) through both holes and tie knots inside so that the string does not slip out. Hold the cups taut, one person speaks softly into their cup while the other listens through theirs. Try the experiment with the string loose (not taut) and then taut. Also try with a longer and shorter string. Record your observations. What does this tell you about how sound travels through solids compared to air?
B. Place your fingertips lightly on your throat and hum at different pitches, low, medium, and high. Now press your fingers gently on a speaker that is playing musi(c) Also touch a table near a playing speaker. Write down what you feel in each case. How does this activity support the statement that ‘sound is produced by vibration’? Do you feel stronger vibrations for low-pitched or high-pitched sounds? Explain your answer.
C. Stand at least 200 m from a large flat wall (a school building or boundary wall works well). Clap your hands sharply and listen for the echo. Adjust your clapping rate until each new clap coincides with the echo of the previous one, at this point, the time between claps equals the echo time. Use a timer to measure 10 such clap-echo cycles and divide by 10 to get the average echo time. Use distance = (speed × time) / 2 to calculate the speed of sound Compare your result with the standard value of speed of sound in air as 344 m s-1 at 22 °C and explain the differences if any.
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