Olympiad Test: Sound - 1 - Class 8 MCQ

• Given: The speed of sound in air is to be determined.


• Options:
  
  
  
  • A: 331 m/s
  
  
  • B: 665 m/s
  
  
  • C: 1550 m/s
  
  
  • D: 173 m/s
  
  
  
  


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  • The speed of sound in air is approximately 331 m/s at standard atmospheric conditions (at 0 degrees Celsius).
  
  
  • This value can vary slightly depending on factors such as temperature, humidity, and pressure.
  
  
  • Sound travels through air as a longitudinal wave, with molecules vibrating back and forth in the same direction as the wave propagation.
  
  
  • The speed of sound in a medium is determined by the medium's temperature and its density.
  
  
  • Higher temperatures and densities generally result in higher speeds of sound.
  
  
  
  

• Vibrations create sound: When an object vibrates, it creates disturbances in the air molecules around it. These disturbances travel through the air in the form of sound waves.


• Frequency of vibrations: The frequency of the vibrations determines the pitch of the sound produced. Higher frequency vibrations create higher pitched sounds, while lower frequency vibrations create lower pitched sounds.


• Amplitude of vibrations: The amplitude of the vibrations determines the volume of the sound produced. Greater amplitude creates louder sounds, while smaller amplitude creates softer sounds.


• Human ear: The human ear is sensitive to these sound waves and can detect them as audible sounds. The ear converts these sound waves into electrical signals that are interpreted by the brain as sound.


• Examples of vibrating objects: Some common examples of vibrating objects that produce sound include musical instruments, vocal cords, and speakers.

• Shrillness of the sound: The shrillness of a sound refers to how high-pitched or piercing it is.


• Frequency of vibration: The frequency of vibration refers to the number of vibrations or oscillations per unit of time. In the case of sound, it is the number of compressions and rarefactions of air molecules per second.


• Relation between shrillness and frequency: The shrillness of a sound is directly related to the frequency of the vibration. Higher frequencies result in a higher pitch or shrillness of the sound, while lower frequencies produce a lower pitch or less shrill sound.


• Amplitude: The amplitude of a sound wave refers to the maximum displacement of air molecules from their rest position. It determines the loudness or intensity of the sound but not the shrillness.


• Noise: Noise refers to any unwanted or unpleasant sound that lacks a specific pitch or frequency. It is different from the concept of shrillness.


• Oscillation: Oscillation refers to the repetitive back and forth movement of particles or waves. While it is related to vibration, it is not the primary factor determining the shrillness of a sound.

Therefore, in the context of determining the shrillness of a sound, the frequency of vibration (option B) plays a crucial role. It directly influences how high or low-pitched the sound is perceived to be.

Men and women have different vocal fold sizes. Adult male voices are usually deeper. Males have larger folds. The male vocal folds are between 17 mm and 25 mm in length.

• Threshold of hearing: The threshold of hearing is the minimum sound level at which a person can hear a sound. It is typically around 0 dB.


• Temporal resolution: Temporal resolution refers to the ability to distinguish between two separate sounds that occur close together in time.


• Temporal integration: When two sounds are presented within a short time interval, the auditory system integrates them into a single percept. This integration occurs for time intervals less than the temporal resolution.


• Difference threshold: The difference threshold is the smallest difference in time between two sounds that can be detected by the auditory system.

• Given: The question asks for the time interval between two sounds that can be heard separately and distinctly by a human being.


• Answer: The correct time interval is 0.1 second (option A).


• Explanation: Human auditory system has a temporal resolution of approximately 0.1 second, which means that sounds separated by 0.1 second or more can be perceived as separate and distinct by the listener.


• Conclusion: Therefore, if two sounds are separated by a time interval of 0.1 second, a human being can hear them separately and distinctly.

• Harmonics: Harmonics are multiples of the fundamental frequency of a sound. They are additional frequencies that are produced along with the fundamental frequency when a sound is produced. The number and relative loudness of these harmonics play a crucial role in determining the quality of a sound.


• Number of Harmonics: The presence of different harmonics gives each sound its unique quality. The number of harmonics present in a sound wave contributes to its timbre, which is the characteristic quality of a sound that distinguishes it from other sounds with the same pitch and loudness.


• Relative Loudness of Harmonics: The relative loudness of harmonics also affects the overall quality of a sound. The amplitudes of the harmonics compared to the fundamental frequency determine the richness and complexity of the sound. A sound with more pronounced harmonics will have a different quality compared to a sound with weaker or fewer harmonics.


• Sound Quality: Therefore, the quality of two sounds with the same fundamental frequency can differ based on the number and relative loudness of their harmonics. These variations in harmonics contribute to the overall perception of sound quality, making each sound unique.

• Frequency of 15 Hz means that the object is vibrating 15 times per second.

• The human hearing range is typically between 20 Hz and 20,000 Hz.


• Sound waves with frequencies below 20 Hz are known as infrasound and are generally not audible to human ears.


• 15 Hz falls below the threshold of human hearing, so the sound produced by the object vibrating at this frequency would not be audible to us.

• Therefore, the correct statement is that the object produces sound which we cannot hear.

• Maximum displacement: Maximum displacement refers to the furthest distance a body moves from its equilibrium position during its oscillation.


• Amplitude: The maximum displacement of an oscillating body is known as its amplitude.


• Definition: The amplitude is the measure of the strength of the oscillation. It indicates the maximum distance the object moves from its rest position.


• Significance: The amplitude is an important parameter in describing the motion of oscillating bodies as it helps in understanding the range of motion and energy involved.


• Relation to Time Period: The amplitude does not depend on the time period of the oscillation. It is a characteristic property of the oscillating body itself.

• Molecules of solids are closely packed as compared to gases: In solids, the molecules are closely packed together, which allows sound waves to travel faster as the molecules can transmit the vibrations more efficiently from one to another. This close proximity between molecules results in a higher speed of sound transmission in solids compared to gases.


• Comparison of the speed of sound: The speed of sound is determined by the medium through which it travels. In solids, the molecules are tightly packed, leading to a faster speed of sound transmission. In gases, the molecules are more spread out, which hinders the efficient transmission of sound waves, resulting in a slower speed of sound.


• Relationship between density and speed of sound: The density of a medium also plays a crucial role in determining the speed of sound. Solids have a higher density compared to gases, which contributes to the faster transmission of sound waves in solids.


• Propagation of sound waves: When a sound wave travels through a solid medium, the molecules are closely packed, allowing the wave to propagate quickly and efficiently. In gases, the molecules are further apart, causing the sound wave to encounter more resistance and resulting in a slower speed of sound transmission.

• Human Audible Range: The audible range of sound frequencies for human beings is the range of frequencies that can be heard by the average human ear.


• Frequency Range: The frequency range of human hearing is typically stated as 20Hz to 20,000Hz.


• Lowest Audible Frequency: The lowest frequency that most humans can hear is around 20Hz.


• Highest Audible Frequency: The highest frequency that most humans can hear is around 20,000Hz.


• Commonly Used Range: While the audible range technically extends from 20Hz to 20,000Hz, most music and speech falls within the range of 50Hz to 5000Hz.


• Answer Justification: Option D, 20Hz to 20,000Hz, covers the full audible range of human hearing and is therefore the correct answer.