Conceptual Questions, Comprehensive Questions, and Numerical Questions KPK Physics Class 10 Notes Chapter 11 Sound the best notes 2021.
Conceptual Questions Physics Class 10 Notes Chapter 11 Sound
Q.1) Why sound produced by a simple pendulum is not heard?
We know that sound is produced due to vibrations of particles of medium and the audible frequency range lies between 20 Hz to 20000 Hz.
When the pendulum swing from one point to another then it will cause vibrations in the particles of air. Frequency of these vibrations is below 20Hz and that is the reason, we cannot hear any sound due to the swinging of pendulum.
Q.2) If a ringing bicycle bell is held tightly by the hand, its stops producing sound. Why?
Vibration of particles in a medium produce sound. When a bell of a bicycle rung it starts to vibrate, due to which sound produces. When this ringing bell is held tightly in hand, it stops vibrating. As a result, not sound produce because there are no vibrations.
Q.3) Why is the intensity of an echo less than that of the original sound?
Intensity is a measure of the amount of sound energy reaching a unit of area in unit time or power per unit area.
Since echo is the reflected sound wave, when the original sound reflects from a surface, part of the sound energy is absorb by the surface as a result the reflected sound wave has less energy as compare to the original sound. Due to the less energy the intensity of echo is less than that of the original sound.
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Q.4) In which medium air or water, an echo is heard sooner? Why?
An echo will hear sooner in case of water as compared to the air.
Sound travels faster in the denser medium. The density of water is larger than air, so sound travels faster in water as compared to air. Due to the greater speed in water, the echo will be heard sooner in water.
Q.5) Why sound cannot be heard on the moon?
As sound waves are mechanical waves and mechanical waves needs some material medium to travel. This medium should consist of particles which can help to transfer the sound energy.
At the surface of the Moon, there is no atmosphere and it is exposed to the vacuum of space, hence it has no material medium. This is the reason, sound waves cannot travel through on the Moon. Therefore, we cannot hear any sound on the Moon.
Q.6) If a person places his ear on rails of railroad for determination of coming train. Why is this done, and how does it work?
People place their ear to the rails of railroad to find out if the train is coming or not. Sound travels faster in denser medium that’s why it travels faster in solids as compare to liquids and gases. The rail tracks are made of metal and sound travels very rapidly though them. The speed of sound through the metal is far more greater then actual speed of the train, so by placing ear on rails we can tell whether the train is coming for not without seeing it.
Q.7) When you watch a thunderstorm, you see the lightning first, and you hear the thunder afterward. Why is the thunder delayed?
During thunderstorm we see lightning first and hear the thunder afterward. The delayed in hearing the thunder is due to the relatively slow speed of sound as compared to the speed of light.
Q.8) If the speed of sound is dependent on frequency, would music for marching band be enjoyed?
If the speed of sound is independent of the frequency. If it depends on frequnecy than due to the motion a band the frequency of the sound will change which results, change in the pitch of the sound. The sound then produced by the marching band would not be uniform and it wouldn’t be as present as it is.
Q.9) Why is it so quite after a snowfall?
It is quiet after a snowfall because the irregular and fluffy surface of snow act as a sound absorber. As a result, most of the sound is absorbed by the snow, which results in quietness.
Comprehensive Questions KPK Physics Class 10 Notes Chapter 11 Sound
Q.1) What is sound? How it is produced, transmitted and received?
The feel that our ear sense is known as sound. It is a form of energy and travels through the medium.
How sound is produced?
In order to produce sound, three things are necessary which are vibrating body, transmitting medium and hearing device.
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1) Vibrating Body:
In everyday life, sound produced in different way as buzzing or bee and mosquito is produced due to vibration of their wings. Sitar and guitar produce sound due to vibration of their strings and similarly by patching on table cause the table surface to vibrate and we hear the sound.
In laboratory, the sound is produced by vibrating the tuning fork. When we struck the prongs of a tuning fork to a hard rubber pad then the prong will vibrate and in result of this vibration, sound will produce in form of compression and rarefaction.
The vibrations produced due to the vibrating body needs a medium to transmit. Vibrations produced by vibrating body supplies energy of its vibrations to surrounding medium. This transmitting medium will transmit this energy from the source to the receiver in form of sound waves.
Transmitting medium can be liquid, solid and gas. Usually transmitting medium is air. However sound cannot be transmit through vacuum.
3) Detection of sound:
The device that can detect or receive the transmitting sound is known as hearing device. Ears are natural hearing device and they convert sound waves into the sensation of hearing. When the sound wave falls to the ear membrane, the membrane will start vibrate and this vibration such that vibrating of the membrane is same as that of vibrating source.
Other than natural, we can also develop some mechanical and electrical hearing devices.
Q.2) What is audible frequency range?
There are upper and lower limits to the sound frequency that humans can hear. A healthy person can hear frequencies in a range from about 20 Hz to 20,000 Hz. Based on the human hearing, the audible frequency range is divided into three parts.
Sound frequencies lower than 20 Hz are referred to as infrasonic. Animals like whales, elephants and rhinoceroses are known to produce infrasonic.
- Audible frequency:
Sound frequencies, ranging between 20 Hz to 20,000 Hz are called audible.
Sound frequencies higher than 20,000 Hz are called ultrasonic. Dog whistle produces ultrasonic. Ultrasounds many applications, they are used in radar systems, medicines and in ultrasonic cleaner.
Q.3) What is the speed of sound?
The speed of sound is the distance traveled per unit time by a sound wave as it propagates through a medium. Like all waves, sound travels at a certain speed. Sound can be transmitted through any medium gas, liquid or solid. The speed of sound depends on the material through which it is passing. The sound travels faster in denser medium that’s why speed is most rapid in certain solid, less rapid in many liquids and quite slowly in most gases., the speed of sound in water is five times greater than the speed of sound in air. The speed of sound ‘v’ is found by:
speed = distance/time
v = S/t
Speed of sound in air:
The speed of sound in air depends upon the density of air and its comprehensibility. As temperature increases , these properties change causing the speed of sound in air to increase. The speed of sound in air at OoC is 331 m/s, for each 1oC rise in temperature the speed of sound increase approximately by 0.6 m/s.
v =331 + 0.6T
here, T is the temperature in oC
Q.4) Describe the terms loudness , pitch and quality. Explain each by giving an example.
Loudness of a sound make us able to distinguish between a loud sound and a faint sound. Loudness of a sound depends on following three factors:
- Area of the vibrating body:
Sound produced has a direct dependence of the area of the vibrating body i.e. larger the area of vibrating body, louder will be the sound produced. That is the reason that the sound produced by school bell is louder than that of produced by house bell and similarly sound produced by the dhool is louder than that of dholac.
- Amplitude of vibrating body:
Sound has a direct dependence on amplitude too i.e. larger the amplitude of the vibrations, louder will be the sound. That is the fact that when we hit the drum harder the sound produced will be louder and the sound will be faint the hit on the drum is gentle.
- Distance from Vibrating Body:
Sound has an inverse relation with the distance between the vibrating body and hearing device i.e. larger the distance, faint will be the sound and vice versa.
Pitch of the Sound:
It is a characteristic of the sound which helps to distinguish a shrill sound from grave sound. It has a direct dependence on the frequency i.e. larger will be the frequency, higher will be the pitch of the sound.
If we take a bicycle and support it by its stand and then start rotating its rear wheel. Then when we take a card board and touch it to the spokes of the rotating wheel then it will start vibrating and in result will produce sound. Now if we increase the rotating speed of wheel then its frequency will also increase and so as the loudness of sound i.e. the sound will become shriller with increase of the frequency.
Quality of Sound:
The property of sound by which two sounds of same loudness and pitch are distinguished from each other is called a quality of sound.
For example we can easily distinguish among the sounds produced by violins, sitars and that of guitars. This is only possible due the difference between their loudness and frequency and pitch related to these sounds.
Q.6) What is noise? Explain why noise is nuisance?
Sound which produce displeasing effects in ear is called noise. Noise produce due to irregular and disordered vibrations.
Excessive displeasing sounds which disrupt the balance or activity of human or animals or other living or non-living things in environment is called noise pollution. There are many sources which produce noise pollution, for example sound of construction machinery, low flying air crafts, loud speakers etc.
Why noise is nuisance?
Noise is nuisance because it has harmful effects on human beings, animals, plants and on other inert things in environment. Some of these harmful effects are as below:
- It can result into temporary or permanent hearing loss.
- This can reduce the working efficiency.
- It can cause an increase in rate of error which will result into different accidents.
- It is a major reason of different dangerous diseases such as blood cancer, blood pressure and heart problems etc.
- It also effects the normal growth rate of plants.
Q.8) What is acoustic protection? Why is it important?
Acoustic protection is the application of soft and porous material to protect individuals against undesirable sounds and noises.
- Acoustic protection is employed not only for physical health but for psychological well being as well.
- Animals and birds have also been reported to express discomfort due to higher noise and sound levels.
- Acoustic protection is necessary to minimize stress levels generated due to high noise.
- It may also be required to protect structures against vibrations generated by objects, such as trains and earthquake.
Numerical Questions Class 10 Physics Notes Chapter 11 (sound)
Q.2) A ship is anchored where the depth of water is 120 m. An ultrasonic signal sent to the bottom of the lake returns in 0.16 s. What is the speed of sound in water?
Distance = S = 2 × 120 m =240 m
Time = t = 0.16s
Speed of sound = v =?
The speed of sound is given by
v = S/t
v = 240/0.16
v = 1500 m/s
Q.5) What is the speed of sound in air at -20oC?
Temperature = T = -20oC
speed of sound = v =?
The general formula for the speed of sound in air at any temperature is
v = 331 + 0.6T
v = 331 + 0.6(-20)
v = 331 – 12
v = 319 m/s
Q.6) Army man wearing binoculars see the flash from enemy tank fire 5 s before the fire is heard, the records 26oC temperature on his personal thermometer. What is the distance of the tank from him?
Time = t =5 s
Temperature = T = 26 oC
Distance to the tank = S =?
The general formula for the speed of sound in air at any temperature is
v = 331 + 0.6T
v = 331 + 0.6(26)
v = 331 + 15.6
v = 346.6 m/s
The the distance covered by the sound is
S = v × t
S = 346.6 × 5
S = 1,733 m
Q.7) Calculate the wavelengths of sounds at the extremes of the audible range, 20 Hz and 20, 000 Hz, at normal room temperature of 20oC?
Lower frequency = fl= 20 Hz
Upper frequency = fu = 20,000 Hz
Temperature = T = 20 oC
a). Wavelength of sound wave at lower frequency = λl = ?
b). Wavelength of sound wave at upper frequency = λu = ?
First we need to find the speed of sound,
v = 331 + 0.6T
v = 331 + 0.6(2o)
v = 331 + 12
v = 343 m/s
The universal wave equation is,
v = fλ
λ = v/f
λl = v/fl
λl = 343/20
λl = 17.15 m
λu = v/fu
λu = 343/20,000
λu = 0.01715 m
λu = 17.15 mm
Q.8) Ishfaq stands two between two high rise buildings A and B, such that he is at 33 m distance from building A. When he blows the whistle, he hears the first echo after 0.2 s and second echo after 0.8 s. Calculate (a) the speed of sound and (b) distance of building B from him.
Distance from building A = SA = 33m
Time to first echo = t1 = 0.2s
Time to second echo = t2 = 0.8s
a). Speed of sound = v =?
b). Distance from building B = SB = ?
Speed of sound using the equation for echo due to building A.
v = 2SA/Δt1
v = 2(33)/0.2
v = 330 m/s
Distance to building B, using the equation for the echo.
SB = (vΔt2)/2
SB = (330 × 0.8)/2
SB = (264)/2
SB = 132 m