Class 9 Sound Waves: Characteristics and Applications Mock Test (CBSE)

Topics in Sound Waves: Characteristics and Applications

• Production of sound
• Propagation of sound and need for a medium
• Sound waves
• Energy of sound waves
• Graphical representation of a sound wave
• Wavelength, frequency and time period
• Amplitude and intensity
• Speed of sound
• Human perception of sound
• Echo
• Reverberation
• Ultrasonic and infrasonic waves and their applications

Sound Waves: Characteristics and Applications practice questions with answers

1. Q1Assertion and reason·1 mark
   Assertion (A): Sound travels faster in humid air than in dry air at the same temperature. Reason (R): The presence of water vapour in air decreases the average molecular mass of air, thereby increasing the speed of sound.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). Both statements are correct and the decrease in average molecular mass due to water vapour directly accounts for the higher speed of sound in humid air, making option (a) correct.+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   Which characteristic of sound is responsible for distinguishing between a man's voice and a woman's voice of the same loudness?

   1. (a)Loudness
   2. (b)Pitch
   3. (c)Speed
   4. (d)Quality or timbre
   Show answer and step marks

   1. Correct option: (b) Pitch+1

   Answer: (b)
3. Q3Multiple choice·1 mark
   A source produces sound waves in a gas. If the absolute temperature of the gas is increased by a factor of $4$ while keeping the frequency constant, what is the ratio of the new wavelength to the original wavelength?

   1. (a)$1:1$
   2. (b)$1:2$
   3. (c)$2:1$
   4. (d)$4:1$
   Show answer and step marks

   1. Correct option: (c) $2:1$. Since the speed of sound $v$ is proportional to $\sqrt{T}$, increasing temperature by a factor of $4$ doubles the speed. With constant frequency, wavelength $\lambda = \frac{v}{f}$ also doubles, giving a ratio of $2:1$, which corresponds to option (c).+1

   Answer: (c)
4. Q4Multiple choice·1 mark
   A person stands between two parallel cliffs and fires a pistol. The first echo is heard after $1.5\text{ s}$ and the second after $2.5\text{ s}$. If the speed of sound is $340\text{ m/s}$, the distance between the cliffs is:

   1. (a)$340\text{ m}$
   2. (b)$510\text{ m}$
   3. (c)$680\text{ m}$
   4. (d)$1360\text{ m}$
   Show answer and step marks

   1. Correct option: (c) $680\text{ m}$. Calculating distances to both cliffs as $d_1 = \frac{340 \times 1.5}{2} = 255\text{ m}$ and $d_2 = \frac{340 \times 2.5}{2} = 425\text{ m}$, their sum is $680\text{ m}$, matching option (c).+1

   Answer: (c)
5. Q5Multiple choice·1 mark
   A sound wave is produced in an iron rod, water, and air at the same temperature. What is the correct order of the speed of sound ($v$) in these media?

   1. (a)$v_{\text{air}} > v_{\text{water}} > v_{\text{iron}}$
   2. (b)$v_{\text{iron}} > v_{\text{water}} > v_{\text{air}}$
   3. (c)$v_{\text{iron}} = v_{\text{water}} = v_{\text{air}}$
   4. (d)$v_{\text{water}} > v_{\text{iron}} > v_{\text{air}}$
   Show answer and step marks

   1. Correct option: (b) $v_{\text{iron}} > v_{\text{water}} > v_{\text{air}}$+1

   Answer: (b)
6. Q6Short answer·3 marks
   Explain the phenomenon of reverberation in large halls. State any two methods commonly used to reduce excessive reverberation in auditoriums.
   Show answer and step marks

   1. Define reverberation as the persistence of sound due to repeated reflections of sound waves from the walls, ceiling, and floor of a large room after the source has stopped.+1
   2. Explain that multiple reflections cause sound to linger and overlap, making speech difficult to understand clearly.+1
   3. First method, any one of: covering the walls and roof with sound-absorbent materials such as compressed fibreboard or rough plaster; hanging heavy curtains (draperies); using seats made of sound-absorbing material; laying carpets on the floor; or any other valid method.+0.5
   4. Second method, a different one from the same list.+0.5

   Answer: Reverberation is the persistence of sound in a large hall due to repeated reflections from the walls, ceiling and floor. Any two of: covering walls and roof with sound-absorbent materials such as compressed fibreboard or rough plaster; heavy curtains; seats of sound-absorbing material; carpets on the floor.

More Class 9 Science mock tests