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Sound is categorized into two types on the basis of frequency perceived by the human ear. These are Inaudible and Audible sounds.
- The frequency of the sound ranges between 20 Hz to 20 kHz and is known as audible sound.
- Audible sounds are easily detectable or sensed by the human ear.
- The frequency of the sound below 20 Hz and above 20 kHz is known as inaudible sound.
- Inaudible sounds are not detected or sensed by the human ear.
- Although it can be used by some animals to communicate with each other.
There are two types of inaudible sound. These are
- Infrasonic sound: The frequency of the inaudible sound whose frequency is below 20 Hz is referred to as the infrasonic sound.
- Ultrasonic sound: The frequency of the inaudible sound whose frequency is above 20 kHz is referred to as the ultrasonic sound.
Very Short Answers Questions [1 Mark Questions]
Ques. The frequency range of audible sound is
- 10 Hz to 12 kHz
- 20 Hz to 20 kHz
- More than 20 kHz
- Less than 10 Hz
Ans. The correct option is b. 20 Hz to 20 kHz
Explanation: A human ear can detect sound whose frequency ranges between 20 Hz to 20000 Hz or 20 kHz.
Ques. Which types of sound are classified as inaudible sounds?
- Above 20 Hz and above 20 kHz
- Below 20 Hz and below 20 kHz
- Below 20 Hz and above 20 kHz
- Above 20 Hz and below 20 kHz
Ans. The correct answer is c. Below 20 Hz and above 20 kHz
Explanation: Inaudible sounds are those which are not detected by the human ear. The frequency of the sound below the lower limit of audibility i.e. 20 Hz and above the highest limit of audibility i.e. 20 kHz are classified as inaudible sound.
Ques. Can inaudible frequencies damage hearing?
Ans. Long-time exposure to inaudible sound can damage the hearing capability of the ear. Subharmonic vibrations are produced in the ear if the ultrasonic sound is excessively powerful, which is inaudible and can cause hearing loss.
Ques. Define Sound.
Ans. A sound wave is a form of energy that propagates through a medium such as air, water, or solids produced by vibrations of molecules of that medium.
Ques. Define the Intensity of sound.
Ans. The intensity of the sound wave is defined as the energy transmitted per unit of time per unit area through the medium of propagation.
The intensity of sound is inversely proportional to the square of the distance from a point source of sound.
Short Answers Questions [2 Marks Questions]
Ques. What are inaudible sounds?
Ans. The frequency of the sound wave that can not be perceived or detected by a human ear is known as inaudible sound. The frequency of inaudible sound is less than 20 Hz and more than 20 KHz. The sound that has a frequency of less than 20 Hz is known as Infrasonic sound. The sound that has a frequency greater than 20 kHz is known as Ultrasonic sound.
Ques. What are the examples of inaudible sounds?
Ans. Examples of inaudible sounds are
- Bats use ultrasonic sound which is an inaudible sound for navigation.
- A dog whistle produced an ultrasonic sound used for the training of the dogs.
- Infrasonic is produced by earthquakes, thunderstorms, and volcanic eruptions.
Ques. What is the pitch of a sound?
Ans. Pitch is the characteristic of sound that depends on frequency. It determines the shrillness or graveness of sound.
The smaller the frequency of the sound, the smaller the pitch, and the greater the frequency greater the pitch.
Ques. What are audible sounds?
Ans. The frequency of the sound wave that can be perceived or detected by a human ear is known as audible sound. The frequency range of audible sound is 20 Hz to 20 KHz. A human ear can’t be able to detect the sound above or below these frequencies.
Ques. What are the examples of audible sounds?
Ans. Examples of audible sounds are
- The sound produced by vibrating sources like guitar strings, drums, and tuning forks is in the frequency range of audible sound.
- Audible sound is used in railway stations to provide information about the timing of trains.
- The sound produced by danger alarms, ambulances, and police vehicles is in an audible frequency range.
Also Read:
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| Intensity Formula | Transverse and Longitudinal Waves | Wave Speed |
Long Answers Questions [3 Marks Questions]
Ques. Define decibel scale? Write the formula of loudness on a decibel scale.
Ans. A logarithmic scale to express the loudness of sound is known as a decibel scale (dB). The minimum intensity of sound that a human ear can detect is known as the threshold of hearing i.e. 10-12 Wm-2 and the maximum intensity of sound that a human ear can detect is known as the threshold of pain i.e. 1 Wm-2. Since this range is fairly large, therefore a logarithmic scale is developed to express loudness. This scale is called the decibel scale.
The formula for loudness on a decibel scale is given by
L (in dB) = 10 log10 (I/I0)
Where
- I is the intensity of the sound
- I0 is the threshold of hearing.
Ques. What are the factors affecting the propagation of sound waves?
Ans. The following are the two major factors that affect the propagation of sound waves
- The density of the medium: Sound waves requires a medium to propagate. The speed of the sound depends on the medium to which it is propagated. The speed of the sound is more if the medium is denser.
- The temperature of the medium: The speed of the sound wave is directly proportional to the temperature of the medium. If the temperature of the medium increases then the speed of the sound wave also increased.
Ques. What are ultrasonic sounds? Write the uses of ultrasonic sound.
Ans. Ultrasonic sounds are high-frequency sound wave that has frequency above the highest limit of audibility of a human ear. The frequency of ultrasonic sounds is greater than 20 kHz.
The applications of ultrasonic sound waves are
- These are used for flaw detection.
- It is used in cutting and matching hard materials.
- It is used in ultrasonic soldering and also welding.
- It is used in the measurement of the flow devices.
Very Long Answers Questions [5 Marks Questions]
Ques. What are the characteristics of sound waves?
Ans. The characteristics of sound waves are
- Amplitude: It is the maximum displacement of the particles of the medium when a sound wave passes through it.
- Wavelength: It is the distance between the centers of two consecutive rarefactions and compressions of a sound wave.
- Frequency: The number of cycles completed per second of a sound wave is known as its frequency. It is measured in Hertz (Hz).
- Time period: The time taken by a sound wave to complete one cycle is known as its time period. It is denoted by T.
- Velocity: The distance covered by a wave in one second is known as the velocity of the sound wave.
Ques. What are the differences between inaudible and audible sounds?
Ans. Following are the differences between inaudible and audible sounds
| Inaudible Sound | Audible Sound |
|---|---|
| These are the sound wave that is not detected by the human ear. | These are the sound waves detected by the human ear. |
| The frequency range of inaudible sound is below 20 Hz and above 20 kHz. | The frequency range of audible sound is between 20 Hz to 20 kHz. |
| Due to a higher absorption rate, some inaudible sounds like ultrasound have a limited range of transmission. | Audible sounds can easily travel in air, water, or other media. |
Ques. What are Infrasonic sounds? Write the uses of infrasonic sounds.
Ans. Infrasonic sound, also known as low-frequency sound wave is a sound that has a frequency below the lower limit of audibility of a human ear. The frequency of infrasonic sound waves is below 20 Hz.
The applications of infrasonic sound waves are
- Many animals like elephants, hippos, rhinos, pigeons, etc. use infrasonic sounds to communicate with each other.
- Volcanic eruptions can be detected using infrasonic sound waves.
- Infrasound can be used to monitor hurricanes, thunderstorms, and tornadoes.
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