Q1: What is the primary requirement for sound to propagate from one place to another? (a) A vacuum (b) A medium such as solid, liquid, or gas (c) Only air (d) High temperature
Solution:
Ans: (b) Explanation: Sound is a mechanical wave that requires a material medium to travel. It cannot propagate through a vacuum, as demonstrated by the bell jar experiment.
Q2: In a longitudinal wave like sound, how do the particles of the medium vibrate? (a) Perpendicular to the direction of wave propagation (b) In circular motion (c) Parallel to the direction of wave propagation (d) They do not vibrate at all
Solution:
Ans: (c) Explanation: In longitudinal waves, particles vibrate back and forth in the same direction as the wave travels. This creates compressions and rarefactions in the medium.
Q3: Which of the following represents the relationship between speed, wavelength, and frequency of a sound wave? (a) v = λ + ν (b) v = λ / ν (c) v = ν / λ (d) v = λ × ν
Solution:
Ans: (d) Explanation: The speed of sound equals wavelength multiplied by frequency. This relationship helps calculate any one quantity when the other two are known.
Q4: What is the minimum distance required from a reflecting surface to hear an echo clearly in air? (a) 34 metres (b) 85 metres (c) 17 metres (d) 10 metres
Solution:
Ans: (c) Explanation: The brain needs at least 0.1 seconds to distinguish between original and reflected sound. With sound speed at 340 m/s, minimum distance is 17 metres.
Q5: Which type of sound waves do bats use for echolocation? (a) Infrasonic waves (b) Audible sound waves (c) Ultrasonic waves (d) Musical notes
Solution:
Ans: (c) Explanation: Bats emit short bursts of ultrasonic waves with frequencies above 20 kHz. They sense the echoes to locate obstacles and prey during flight.
Fill in the Blanks
Q1: Sound is produced by the _____ of objects.
Solution:
Ans: vibrations
Q2: The SI unit of frequency is _____ or per second.
Solution:
Ans: hertz
Q3: Regions of high density in a sound wave are called _____.
Solution:
Ans: compressions
Q4: The human audible range of frequencies is from 20 Hz to _____ Hz.
Solution:
Ans: 20,000
Q5: The persistence of sound in a large hall due to multiple reflections is called _____.
Solution:
Ans: reverberation
True or False
Q1: Sound can travel through vacuum.
Solution:
Ans: False Explanation: The bell jar experiment demonstrates that sound cannot propagate in vacuum. Sound requires a material medium to travel through.
Q2: The speed of sound is fastest in solids and slowest in gases.
Solution:
Ans: True Explanation: Sound travels fastest through solids, slower through liquids, and slowest through gases due to differences in particle arrangement and density.
Q3: In sound wave propagation, the particles of the medium travel along with the wave.
Solution:
Ans: False Explanation: Particles only vibrate about their mean positions. It is the energy and disturbance that travels, not the actual medium particles.
Q4: Frequency and time period are inversely related to each other.
Solution:
Ans: True Explanation: The relationship is expressed as ν equals one divided by T. A shorter time period corresponds to a higher frequency.
Q5: Dogs can detect ultrasonic waves that humans cannot hear.
Solution:
Ans: True Explanation: Dogs, cats, bats, and dolphins can detect ultrasound with frequencies above 20 kHz, which is beyond the human audible range.
Match the Following
Column A
Column B
1. Wavelength
A. Number of oscillations per unit time
2. Amplitude
B. Frequencies below 20 Hz
3. Frequency
C. Distance a crest travels per unit time
4. Infrasonic waves
D. Distance between two consecutive crests
5. Speed of sound
E. Maximum change in density from average
Solution:
Ans:
1 - D: Wavelength is defined as the distance between two consecutive crests or troughs in a wave pattern.
2 - E: Amplitude represents the maximum change in air density in a compression or rarefaction compared to average density.
3 - A: Frequency is the number of density oscillations at a fixed point per unit time, measured in hertz.
4 - B: Infrasonic waves have frequencies below 20 Hz and cannot be heard by humans but are used for detecting earthquakes.
5 - C: Speed of sound is the distance which a point on a wave travels in unit time through a medium.
Short Answer Questions
Q1: Explain how sound is produced in humans.
Solution:
Ans: Sound in humans is produced by the vibration of vocal cords, which are tightly stretched muscular flaps located inside the voice box or larynx in the throat. When air from the lungs passes through the vocal cords, they vibrate and produce sound. The tongue, lips, mouth, and nasal cavity help convert this sound into speech or music.
Q2: What happens to the intensity of sound as it travels away from its source?
Solution:
Ans: As a sound wave travels away from its source, it spreads over a larger area. Since energy must be conserved, the same amount of energy is now distributed over a larger area, causing the intensity to decrease with distance from the source. Sounds with larger initial amplitude carry more energy and can travel farther before intensity reduces to zero.
Q3: Describe the vacuum bell jar experiment and its conclusion.
Solution:
Ans: An electric bell is placed inside a bell jar and switched on, producing audible sound. As air is gradually pumped out using a vacuum pump, the sound becomes fainter. When near-vacuum is reached, almost no sound is heard even though the bell can be seen ringing. When air is let back in, sound is heard again. This demonstrates that sound cannot propagate in vacuum.
Q4: What is echolocation and which animals use it?
Solution:
Ans: Echolocation is the ability to locate objects using reflected sound waves. Bats are nocturnal creatures that emit short bursts of ultrasonic waves and sense the echoes to determine the position of obstacles and prey, enabling them to fly and hunt in darkness. Besides bats, dolphins, whales, and some birds also use echolocation for navigation and hunting purposes.
Q5: Why are auditoriums designed with sound-absorbing materials?
Solution:
Ans: Modern auditoriums are architecturally designed to achieve desirable reverberations and prevent unwanted sound reflections. When sound undergoes multiple reflections from walls in a large hall, it can persist after the source stops, creating garbled or unclear sound. Sound-absorbing panels, upholstered chairs, curtains, and other soft, porous surfaces reduce excessive reverberations, ensuring clear and pleasant sound quality.
Long Answer Questions
Q1: Explain the formation of compressions and rarefactions in a sound wave using the piston model.
Solution:
Ans: Consider a long tube filled with air and an oscillating piston at one end. When the piston moves forward, it pushes air particles near it, increasing air density in that region, forming a compression. This high-density region moves forward as compressed particles collide with neighbouring particles. When the piston moves backward, air near it becomes less dense, creating a rarefaction. As the piston oscillates, compressions and rarefactions are produced alternately and travel away from the source, forming a sound wave.
Q2: How does a microphone convert sound energy to electrical energy, and how does a speaker reverse this process?
Solution:
Ans: A microphone converts sound energy to electrical energy by using a thin membrane called a diaphragm. When sound waves reach the microphone, they make the diaphragm vibrate. These mechanical vibrations are then converted into electrical signals. A speaker does the opposite process. It receives electrical signals which make a cone or diaphragm inside it vibrate. These vibrations produce sound waves that closely match the originally captured sound, thus recreating the audio.
Q3: Analyse the differences between pitch and loudness in terms of their physical properties and human perception.
Solution:
Ans: Pitch is how humans perceive the frequency of a sound wave. Shrill sounds like whistles have high pitch and higher frequency, while deep sounds like thunder have low pitch and lower frequency. Loudness is how humans perceive the amplitude of a sound wave. Larger amplitude is heard as louder sound, while smaller amplitude sounds softer. Pitch depends on frequency, a measurable physical property, whereas loudness depends on amplitude and also on the listener's hearing ability, making it partly subjective.
Important questions, shortcuts and tricks, MCQs, Worksheet with Solutions: Sound Waves: Characterstics and Applications, Objective type Questions, ppt, Summary, Free, Extra Questions, study material, pdf , Viva Questions, Worksheet with Solutions: Sound Waves: Characterstics and Applications, Semester Notes, Sample Paper, past year papers, Worksheet with Solutions: Sound Waves: Characterstics and Applications, practice quizzes, mock tests for examination, video lectures, Previous Year Questions with Solutions, Exam;
