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Sound is a form of energy that is a result of vibrations. It yields hearing sensations. There are two forms of sound waves that exist in nature namely transverse waves and longitudinal waves. A sound wave is an example of a longitudinal wave while a light wave can be an example of a transverse wave.
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Key Takeaways- Sound, Vibration, Compressions, Rarefactions, Reflection, Navigation
Sounds
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A sound is a form of the longitudinal wave which causes a hearing sensation in our ears. It needs a medium to travel which means it cannot travel in a vacuum. It is a form of a mechanical wave. The substance or material through which sound is produced is called a medium. It moves through a medium with the help of expansion and contraction that occurs in a medium alternately.
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Characteristics of Sounds Waves
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The different characteristics of a sound wave include:
Frequency
In a unit of time, the number of rarefactions or compressions is called frequency. Its unit is Hertz and is denoted by Hz. The formula of frequency: ν=1T. The relation between speed(v), wavelength(λ) and frequency(ν) is v= λν.
Amplitude
The magnitude possessed by the highest disturbance in the medium on any one side of the mean value is called the amplitude of any wave. It is denoted by A. The unit of amplitude is meter.
Speed
The distance covered by rarefaction or compression covered per unit time is called the speed of sound. The speed of sound is highest in the case of solids while it is lowest when it comes to gases. It is intermediate in the case of liquids.
Quality of Sound
The richness which a sound possesses is called a quality of sound. The quality of a sound can be determined by the pitch and its loudness.
Volume
An object that vibrates with a force gives rise to the loudness or volume of a sound. The higher the sound, the higher will be the amplitude, the louder the sound.
Time Period
Time required by two successive compressions or rarefactions to pass a static point is called the Time Period. It is denoted by T and its unit is seconds(s).
Wavelength
The distance between two consecutive rarefactions and compressions or troughs or crests is called wavelength. It is denoted by λ measured by the meter (m).
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Types of Sounds Waves
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In general, there are three types of sound that exist in nature. These are:
Infrasonic
The frequency of infrasonic sound waves is below 20 Hz. It is used by the elephants to communicate with their herds which are miles away.
Sonic
The frequency of sonic sound waves is in the range of 20 Hz to 20,000 Hz. The sonic sounds are the sounds that cannot be heard by the human ear.
Ultrasonic
The frequency of ultrasonic sound waves is above 20,000 Hz. These high-frequency sounds can be heard by some animals like dogs and bats.
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Structure of Human Ear
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A human can perform the function of hearing with the help of a human ear which is a sensitive organ. It is required to complete the process of detecting the sound, transmitting, and then transducing it. It also aids in maintaining balance. The structure of the human ear includes:
- Pinna is the outer ear or we can say it is the visible area of an ear to a human.
- The pinna is responsible for collecting the sounds available in the surroundings.
- The auditory canal is a tube that passes the sound.
- If an incident sound wave occurs, the eardrum or the tympanic membrane vibrates to respond to the incident wave.
- The three bones namely anvil, stirrup, and hammer which are present in the region of the middle ear to the inner ear allow the vibrations to get amplified and transmitted.
- The cochlea which is present in the inner ear is responsible for converting the pressure signals to electrical signals.
- To make the electrical signals understandable by the brain as sound and for the interpretation, they are transmitted by the auditory nerve.
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Points to Remember
Following are some important points:
- Sound is the result of continuous vibrations and is a mechanical wave which is a form of energy.
- Sound requires a medium to travel and thus it cannot be travelled in a vacuum.
- The reflection of sound waves includes phenomena such as echo, sonar and radar, reverberation, and doppler’s effect.
- The formula of frequency is ν=1T.
- The functions of the human ear include the detection, transmission, and transduction of sound.
- Scientifically, the outer ear is called the pinna and the auditory nerve is responsible for transmitting a sound wave to the brain for interpretation.
Sample Questions
Ques: State the relation that exists between wavelength, speed, and frequency. (2 Marks)
Ans: The relation among the speed, wavelength, and frequency denoted by v, λ, and ν is given by v= λν. Frequency is defined as the total number of compressions or rarefactions in a unit of time.
Ques: What is SONAR and RADAR? (4 Marks)
Ans: SONAR can be known as Sound Navigation and Ranging. It is a method to calculate distance using ultrasonic waves or sound. The range of hearing for a human ear is 20Hz-20KHz. Ultrasounds are used in detecting the cracks found in metal blocks, detecting/communicating/navigating the things found on or under the water, and scanning the human organ images. It has a transmitter and a detector which is placed on a boat or ship. The ultrasonic sound waves are sent by the transmitter to the bed of the sea and are then received by the detector. When the speed of the sound is known, the formula to measure the distance = 2d=v×t. This process is called echo ranging or echo-location.
Ques: Define wavelength. (2 Marks)
Ans: The wavelength of the sound is the distance between two consecutive rarefactions and compressions or troughs or crests. It is measured in metres (m). It is denoted by λ. Wavelength is one of the major characteristics possessed by the sound wave.
Ques: State the three major bones present in the human ear. (2 Marks)
Ans: The human ear consists of three major bones including the anvil, stirrup, and hammer. They are present in the region between the middle ear to the inner ear. The function of these bones is to amplify and transmit the sound waves.
Ques: Explain the waves and the types of waves. (3 Marks)
Ans: Disturbance in any medium which causes the other particles to move can be termed as waves. There are two types of waves namely transverse wave and longitudinal wave. The transverse wave is the particle movement that is perpendicular to the direction while the longitudinal wave is the particle movement across the direction. A light wave is an example of a transverse wave and a sound wave is an example of a longitudinal wave.
Ques: What is reverberation? (2 Marks)
Ans: The persistence of sound which results due to multiple refractions is called reverberation. A simple example of reverberation is an auditorium. Excessive reverberation is not termed good and to get rid of it, we use sound-absorbing materials such as fibreboard. An example of reverberation can be the auditorium.
Ques: What is the range of frequency that can be heard by the human ear? (2 Marks)
Ans: The range of hearing for a human ear is 20Hz-20KHz. Above 20 KHz, the sound waves are called ultrasonic waves which fall under the inaudible range which means that this sound cannot be heard by a human ear. However, animals like dogs and bats can hear this type of sound.
Ques: What is Doppler’s Effect? (2 Marks)
Ans: A change of frequency is noticed if there’s a change in either the observer or the source of the sound, this is termed as the doppler’s effect. The frequency increases as the observer comes towards the source and decreases when it moves away from the source. For Example: A person hears more sound if the ambulance comes near him/her and hears less sound when it passes away.
Ques: What do you mean by Echo? (2 Marks)
Ans: In this phenomenon, the sound is bounced back and is repeatedly heard due to reflection. An example of an echo can be the clapping of hands or shouting from a mountain. The interval of time to hear an echo should be of at least 0.1 seconds and the minimum distance should be 17.2 m. One can also hear multiple echoes which are caused by multiple reflections.
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