## Class 9 Science Case Study Questions Chapter 12 Sound

Case study Questions in Class 9 Science Chapter 12 are very important to solve for your exam. Class 9 Science Chapter 12 Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving Class 9 Science Case Study Questions Chapter 12 Sound

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In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

# Sound Case Study Questions With Answers

Here, we have provided case-based/passage-based questions for Class 9 Science Chapter 12 Sound

Case Study/Passage-Based Questions

Case Study 1: A violin and a flute may both be played at the same time in an orchestra. Both sounds travel through the same medium, that is, air and arrive at our ears at the same time. Both sounds travel at the same speed irrespective of the source. But the sounds receive are different. This is due to the different characteristics associated with the sound. Pitch is one of the characteristics. How the brain interprets the frequency of emitted sound is called its pitch. The faster the vibration of the source, the higher the frequency and the higher the pitch. The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave. It is usually represented by the letter (A).

The loudness or softness of a sound is determined basically by its amplitude. The amplitude of the sound wave depends upon the force with which an object is made to vibrate. If we strike a table lightly, we hear a soft sound because we produce a sound wave of less energy (amplitude).

The quality of timbre of a sound is that characteristic that enables us to distinguish one sound from another having the same pitch and loudness. The sound which is more pleasant is said to be of rich quality. A sound of a single frequency is called a tone. The sound which is produced due to a mixture of several frequencies is called a note and is pleasant to listen to. Noise is unpleasant to the ear! Music is pleasant to hear and is of rich quality.

(i) Pitch of sound is higher when

(a) Vibration of the source of sound is higher

(b) Vibration of the source of sound is Lower

(c) Independent of vibration of the source of sound

(d) None of these

Answer: (a) Vibration of the source of sound is higher

(ii) Loudness and softness of sound depend upon

(a) Frequency of sound

(b) Amplitude of sound

(c) Wavelength of sound

(d) None of these

(iii) Sound of single frequency is called

(a) Note

(b) Tone

(c) Noise

(d) None of these

(iv)If we strike a table lightly, we hear a soft sound. If we hit the table hard we hear a louder sound up to a large distance. Why?

Answer: If we hit the table hard we hear a louder sound because A sound wave spreads out from its source. As it moves away from the source its amplitude as well as its loudness decreases. Louder sound can travel a larger distance as it is associated with higher energy.

(v) Determine which of the following has a higher pitch railway horn or guitar?

Answer: Pitch of sound depends on the frequency of vibration of waves and if the frequency of vibration is higher we say that the sound has higher pitch. Pitch of the sound is the response of our ear. So, basically guitar has 6 strings and the sharpness of each string increases on going below. On the other hand in car horns, there is flat pitch with high noise which can affect anyone’s heart too. As guitar has higher frequency than car horn as number of vibrations per unit time of guitar string are more than car.

Case Study 2: Sound bounces off a solid or a liquid like a rubber ball bounces off a wall. Like the light, sound

gets reflected at the surface of a solid or liquid and follows the same laws of reflection. The directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane. If we 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 that we hear is called an echo. The sensation of sound persists in our brain for about 0.1 s. To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s. Hence, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be 17.2 m. This distance will change with the temperature of the air. Another phenomenon of reflection of sound is reverberation. 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. The repeated reflection that results in this persistence of sound is called reverberation. Excessive reverberation is highly undesirable.

(i) Which of the following is true related to the reflection of sound?

(a) Directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence.

(b) Incident wave reflected wave and normal lies in the same plane

(c) Both a and b are true.

(d) None of these

Answer: (c) Both a and b are true.

(ii)For hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be

(a) 10m

(b) 20m

(c) 17.2m

(d) None of these

(iii) Excessive reverberation is

(a) Desirable phenomenon

(b) Undesirable phenomenon

(c) Does not exist

(d) None of these

(iv) A person makes a sound near an obstacle and heard the echo after 1 s. What is the distance of the obstacle from the person if the speed of the sound, v is taken as 346 m/s?

Answer: Given, Speed of sound, v = 346 m/s Time taken for hearing the echo, t = 1 s Distance travelled by the sound= v × t = 346 m/s × 1 s = 346 m In 1 s sound has to travel twice the distance between the obstacle and the person. Hence, the distance between the obstacle and the person= 346/2 = 173 m.

Case Study 3:

Sound is a form of energy that produces a sensation of hearing. It is produced by the vibration of objects. When an object vibrates, it creates sound waves that travel through a medium, such as air, water, or solids. Sound waves are mechanical waves that require a medium for propagation. They travel in the form of compressions and rarefactions, creating a series of high-pressure and low-pressure regions. The characteristics of sound include pitch, loudness, and quality. Pitch is determined by the frequency of the sound waves, with higher frequencies corresponding to higher pitches. Loudness is related to the amplitude of the sound waves, with larger amplitudes resulting in louder sounds. The quality of sound refers to its timbre, which is influenced by the presence of overtones and harmonics. Understanding the properties and behavior of sound waves helps us comprehend various phenomena, such as the production of musical notes, the propagation of sound, and the phenomenon of echoes.

What is sound?
a) A form of light energy
b) A form of mechanical energy
c) A form of electrical energy
d) A form of heat energy
Answer: b) A form of mechanical energy

How is sound produced?
a) By the reflection of light waves
b) By the absorption of heat energy
c) By the vibration of objects
d) By the flow of electrical current
Answer: c) By the vibration of objects

What do sound waves require for propagation?
a) Light
b) Heat
c) Medium
d) Electricity

What determines the pitch of a sound?
a) The amplitude of the sound waves
b) The frequency of the sound waves
c) The loudness of the sound waves
d) The quality of the sound waves
Answer: b) The frequency of the sound waves

What is the quality of sound?
a) The timbre of the sound
b) The amplitude of the sound waves
c) The loudness of the sound waves
d) The pitch of the sound waves
Answer: a) The timbre of the sound

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