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Sound can be defined as the form of energy which has the ability to generate a sensation in the ear. Sound requires a medium to transfer which is air most of the time. The human ear can only hear sounds between the range 20Hz to 20K Hz. The important things which will be learnt in this chapter are the components of waves and frequency, wavelength, time period and amplitude. The principle of sound waves and its characteristics are used in many applications such as sonar, radar, etc.
Very Short Answer Questions [1 Mark Questions]
Ques: What is pitch?
Ans: It is the sensation of a frequency. The sound can be of higher or lower pitch depending on the frequency of sound waves.
Ques: Which frequency of sound wave is considered as high pitch and which is low?
Ans: Frequency of 880 Hz or above is considered as high pitch and the one with 55 Hz and below is said to be a low pitched sound.
Ques: What is the audible range for the human ear?
Ans: the range of frequency between 20Hz to 20K Hz is said to be the audible range. The frequency below or above this range is not audible.
Ques: Find the wavelength of the sound with the frequency of 20Hz?
Ans: v = n×λ
Taking n as 344 m/s
λ = v/n = 344/20 = 17.2m
Ques: What is the doppler effect?
Ans: The fluctuation which is observed in the intensity of the sound due to the variation in the distances is known as the doppler effect. One of the common examples is the use of loudspeakers and its increase in intensity with the distance of the speaker and the person.
Ques: What is an example of a mechanical wave?
Ans: Sound waves are the best example of mechanical waves. The reason behind this is that sound waves need a medium to propagate by interacting with the particles in the medium.
Short Answer Questions [2 Marks Questions]
Ques: Does the law of reflection is also followed by sound?
Ans: Yes, this is because the angle of incident and the angle of reflection is equal. Therefore all the three laws of light will be followed by sound.
Ques: The sound wave is traveling at a speed of 341 m/s. If the wavelength is 1.2 cm. What will be the frequency of the wave?
Ans: the formula which can be used is v = λV
341 = 0.012 * v
v = 341/0.012
= 28416 Hz
Ques: What is the working of a Sonar?
Ans: The full form of sonar is Sound Navigation and Ranging. This device can be used to estimate the direction, distance and speed of objects underwater by using ultrasonic waves. The device consists of two things: a transmitter and a detector. The work of the transmitter is to produce power ultrasonic waves. The Waves when striking the objects underwater reflect back and are received by the detector. The work of the detector is to convert them into electrical signals which can be interpreted.
Ques: the sonar device receives a signal 10 sec later after sending the signals. What is the speed of the sound if the distance between the object and the submarine is 3625m?
Ans: The distance which is traveled by the sonar waves is twice the distance between an object and a submarine. Therefore the distance is 2*3625 which is 7250m.
Speed = Distance/Time = 7250/10 = 725 m/s
Ques: Which wave property determines (a) Loudness (b) Pitch
Ans: (a) The amplitude and the loudness are directly related to each other. Both are directly proportional therefore greater the amplitude louder will be the sound produced.
(b) For the pitch, the frequency of the wave is related to the pitch. For the sound which has a high frequency then the pitch will also be high.
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| Unit of Sound | Loudness of Sound | Production and Propagation of Sound |
Long Answer Questions [3 Marks Questions]
Ques: What is a wave? What are the types of waves?
Ans: A wave can be defined as the disturbance that travels in a medium. A period motion of the particle is observed in such a way that the disturbance will be passed on from one point to another without the actual movement of the media.
There are two types of mechanical waves: Transverse and longitudinal waves
Transverse wave: In this type of wave the vibration of the media is perpendicular to the direction of propagation of the wave.
Longitudinal wave: In a longitudinal wave the movement of the vibration is in the direction of the propagation of the wave.
Ques: How does a sound which is produced by a vibrating object in a medium reach your ear?
Ans: The sound propagates through air. If we take the example of a vibrating fork, when it moves forward, it will compress the air molecules in front of it. This will create an area of high density and high pressure called compression. This compressed air will move forward. Similarly, when the fork is moved backwards an area of low compression and density will be created. This will be called refraction. As this process continues with the vibrating fork, an area of alternating compression and rarefaction is formed. This will be formed at the same area but the energy generated will travel forward. When this will touch the eardrums and thus sound will be heard.
Ques: Define the following terms:
(i) Frequency
(ii) wavelength
(iii) amplitude
(iv) time period
Ans:
(i) Frequency: The number of compression and rarefaction which passes through a point in one second is called frequency.
(ii) Wavelength: The linear distance between two consecutive compression or two consecutive refractions is called wavelength.
(iii) Amplitude: The magnitude of maximum displacement of a vibrating particle is called amplitude.
(iv) Time period: The time taken by two consecutive rarefactions or compression to cross a particular point is called a time period.
Very Long Answer Questions [5 Marks Questions]
Ques: What is the mechanism of hearing?
Ans: The outer ear called the pinna helps in the collection of sound. The middle ear helps in the amplification of the vibration and the inner ear helps in the conversion of sound into electrical signals.
The collected sound will pass through the canal known as the auditory canal. At the end of the canal an eardrum is present which will vibrate when the sound reaches the eardrum. This will create an area of compression and rarefaction. The middle bone consists of three bones which will amplify the sound so that the sound is transmitted to the inner ear. It is here when the sound is converted into electrical signals and sent to the brain for interpretation.
Ques: What is the application of ultrasound?
Ans: The ultrasounds are the high-frequency waves, it has the ability to travel through a path even if there is a hindrance in between.
Some of the applications of ultrasounds are as follows:
- Ultrasonic waves can be used in echocardiography in which it captures the image of the heart and will depict the problems which might be associated with the heart.
- One of the common examples of ultrasound waves is ultrasound scans. These scans are used to get the images of the internal body organs such as the uterus. This helps in the diagnosis and treatment of the problems of the patients.The waves will travel through the body and the reflected wave which will then be converted into electrical signals and can be monitored on the screen.
- Bats use these ultrasonic waves to hear their prey at night. The wave when hit the prey echoes and allows the bat to judge the distance and attacks the prey accordingly.
- The proper growth of the fetus can be observed with the help of ultrasonography. This will help the doctor to detect the abnormalities if any.
- Sonar is another amazing use of ultrasonic waves. This will help to detect the direction and distance of the object which is present beneath the water.
Ques: What are the regions of air produced by the loudspeaker? How is the sound produced by your school bell?
Ans: An area of high pressure and a region of low pressure are created by the loudspeaker which is called compression and rarefaction respectively. These regions are produced by the movement of the cone of the loudspeaker in the forward and backward directions. If the movement is in the direction of propagation of the wave the air will be compressed to form a compression region which is of high pressure. Similarly, when the cone is moved backwards, a region of low pressure is generated forming rarefaction.
The sound which is produced by the school bell reaches our ear with the help of the vibrating particles. When the bell is hit, it starts vibrating thus compelling the surrounding particles to also vibrate, which then necessitates the adjacent particles to vibrate. In this way the sound is transferred from one particle to another till it reaches our ear.
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